Ask The Guru

Welcome to our Ask The Guru section. You can use the categories below to search through FAQs that our visitors have asked in the past to really broaden your knowledge on how radiant barrier, attic insulation and ventilation work together to help lower your energy costs and make your home more comfortable. Or, you can simply ask me a question and get an answer via return email. Your question will then be added to our list for the benefit of others. down the road.

Check the categories below and if your question falls into one of them, click that link to ask your question.

Thanks for visiting today and for your interest in radiant barrier.

Ed Fritz,
The Radiant Barrier Guru


  1. What does radiant barrier cost to install in my attic?

    Thanks for your question. We are a manufacturer & distributor only, we do not do the installation. Because prices vary by home, location, size, etc. we suggest you hire/find someone in your area who can install the foil.

    If you live in the following areas:
    Texas (Dallas/Ft Worth, Houston, San Antonio, or Austin), Oklahoma (Oklahoma City), Georgia (Atlanta), or Idaho (Boise) then you might try starting your search for an installer here:

    Other options are asking a handyman, an off-season roofer or air conditioning professional, or some young able-bodied college kids.

    Best of luck!

  2. I see radiant barrier products sold for under slab installation, especially for use with a heated slab. My question is about air space being needed for reflectivity or emissivity or work. It seems that a pouring a cement slab over a radiant barrier pretty much takes all the air out of the situation. How are these products working? Thanks, Jim

    You are correct, if the foil is on top or bottom of the insulation, then it will loose it's ability to be a radiant barrier since the aluminum layer is "sandwiched" between the insulation and the concrete or the insulation and the ground. Without an airspace, you cannot have radiant heat (you only have conductive heat flow in this circumstance) and if no radiant heat exists then you can't have a "radiant barrier." Don't waste your time or money putting any type of foil insulation under a slab. I'd go with a foam board or something that can provide some extra R-value.

  3. Will a Radiant Barrier increase the possibility of Ice Damming?

    A radiant barrier will usually REDUCE the possibility of ice damming. Ice damming is caused when the top of the roof warms above the freezing point the the lower part of the roof is below freezing. To prevent ice damming, you want a COLD roof. The roof gets warm due to warm air leakage into the attic AND from the home emitting radiant heat. A radiant barrier will help keep the radiant heat emitting from the home from hitting the roof. The result is a COLDER roof deck which will reduce ice damming. Many customers have seen a significant reduction in ice damming after installing AtticFoil radiant barrier. I would also suggest checking to make sure you have good attic ventilation. Cold air entering the attic will also help keep the roof COLD.

  4. Hi Ed, You have answered so many of my questions (over heating the shingles, ice damming, not over thinking air flow, learning about radiant and conductive heat, product comparisons and many others) on your previous post. I also appreciate your other helpful tips like sealing the duct work and the best way to insulate it. I am feeling very empowered with my new education to tackle the job myself and do the best thing for my house. I hope you will indulge me with your Guru advice on my particular attic circumstance. I have a vented attic. The soffit has a vented strip that runs the entire length of each of the eaves. At the top of the attic there is one gable vent and one electric fan placed about 4 feet down from the ridge and towards the opposite end of the gable vent. My rafters have an actual measurement of 1 1/2" by 7 1/4". When I finally need my shingles replaced I would like to get rid of the fan and alter the roof to have a ridge vent. My attic space is less than 6'tall at the ridge height and has lots of floor space (about 33' by 75'). The long triangle space is is very open without lots of braces, cross beams or any collar beams. The floor houses lots of duct work and dual zone gas furnace. There is plenty of room for storage but the temperatures are so extreme, it is not the best place for many things I would like to store. I have loose insulation on the floor of the attic and would like to put down a plywood floor for convenience and cleanliness. I wondered about first placing dense foam board on top of the joist and then plywood on top of that. My goal is to reduce the extreme cold AND hot temperatures in the attic, enclose the loose floor insulation, have a clean safe place for storage and hopefully some worthwhile energy savings and efficency. Right now the outside temperature is 36 degrees, the attic temperature is 43 degrees and the house is 72. Here is where I need your help to determine the best combination of AtticFoil and insulation for my circumstance and goals. My first idea is to staple the AtticFoil to the rafters making 7 1/4" by 15" vented shafts from soffit to ridge. Is a bigger air shaft better than a smaller one? What is the most efficient amount air space? Alternately, I could staple the AtticFoil to make a smaller 3" by 15" air shaft and fill the balance of the rafter space with insulation. At this point, I wonder if the insulation should be batting, foam board, spray foam or other product. Should the insulation touch the AtticFoil or have an air space on the bottom side of the foil as well. So, for example, from the roof down could be the roof, 3" air space, AtticFoil, 4 1/4" air space, foam board insulation attached to the joist edge, the open room area, plywood, foam board, and joist filled with loose insulation. What would you suggest as the best combination? I can see that closing up the rafters will make the electric fan serve only one rafter shaft as it will be closed to all other rafter shafts. Is one gable vent enough? Maybe I should get the ridge vent in place first. What would you suggest? Thank you for your advice. Sincerely, Karen Thomas


    The size of the vent shaft does not really matter too much. The air is using a natural "stack effect" not under pressure. So, I'd just staple to the bottom of the rafters and keep it easy and simple. I would only go with radiant barrier and NO bulk insulation on the bottom of the roof. You want insulation on the attic floor to be in direct contact with the "thermal envelope" or your room ceiling. This same principle is why we put a blanket directly on top of us, and don't levitate it two feet above our bed - it wouldn't do any good if it wasn't on our body. You will want to install and leave an airspace at the top and bottom of the roof slopes. Also, cut a hole in the foil below the fan. Basically, you want air to flow through the attic as though the foil does not exist.

    As for the layers: Roof => Air Space the thickness of the rafters => AtticFoil => Attic "open" area => Plywood flooring => Foam board (optional based on how much R-Value you want and your budget) => loose filled insulation (this needs to completely fill the ceiling joists) => Drywall

    I would switch to a ridge vent when the roof is replaced. For now, make sure you soffit vents are clear and open, allowing air to come INTO the attic. Clogged/insufficient soffit vents are the number one problem with attic ventilation.

  5. Hi Guru! I have a question about radient barriers in metal buildings. We own a metal building with a darker green metal roof. The building is about 5000 sq ft. I'm wondering if it would be a good idea to use a radient barrier in the attic. Or does the metal roof provide a sufficent radient barrier? Also the under side of the roof is white. If I install a barrier and leave the required space will this pose a problem by reflecting the heat back onto it? Thanks!!

    Metal roofs can vary greatly in their ability to reflect radiant heat.

    If it FEELS hot near the roof, then a radiant barrier will be very beneficial. A green metal roof is typically not very reflective, so it probably is absorbing most of the radiant heat. There is no risk from reflecting the heat back towards the roof. Typically the roof temperature over a radiant barrier will only increase a few degrees compared to a roof without a radiant barrier.

  6. Hi Ed, I'm finally to the point of being stuck after reading SO much information concerning venting vs. non-vented attic, ice damns & insulating duct work. This is our first full winter in a newly constructed house. We opted to have the attic rafters sprayed with spray-foam insulation, so we have a non-vented attic. When the snow began to fly in December we discovered major ice damning all around the house (one of which fell and injured by husband). The insulation company came back and used an inferred (sp?) camera to detect any heat loss - they found a few small places and fixed those. It still didn't fix the problem. We have two air converters for our 2nd floor heat along with hot water tubing and all the duct work running through the attic. They found a significant amount of air leaking in the duct work, so came back and insulated the duct work along with the hot water tubing, hoping to bring down the heat in the attic. The heat did decrease quite a bit but this still has not fixed the ice issue. We had a warm front last week and were able to remove the 12 inch ice damns on the roof line and were hoping the added insulation on the duct work would take care of the problem. We have ice damns again. We live in the Northeast with significant amounts of snowfall for six months of the year. Can you give me any ideas as to what else we might be able to try? Can/should we give up on the non-vented attic idea at this point and just vent the attic and insulate the attic floor? Any help would be greatly appreciated!

    I would not give up on the non-vented attic. You spent good money for this feature and you should try to figure out how to fix it.

    The real question is why is the top part of the roof getting warm enough to melt the snow/ice but the bottom part is staying cold?

    There are so many questions to ask: Is it concentrated in one area? - If so, you could have some significant thermal bypass or voids in the foam that is allowing the heat to get behind or through the foam. How much foam did they apply? Did they completely cover the bottom of the rafters? Closed or open cell foam?

    From what you are telling me, I'd focus on the duct leakage if it is all over the roof. One leaky duct can fill the attic with hot air and it will naturally rise to the top. This "extra" heat can pass through ANY amount of insulation over time. This would cause the top to melt resulting in ice dams. Have you measured the AIR temperature near the top of the attic? Ideally it would be a few degrees BELOW the set point inside the house? If its hotter, this is a sure sign of duct leakage. Check both the supply and the return air side for leakage. A leaky duct on the return air side can be harder to find and will cause the attic to go under negative pressure. Then it will SUCK air from inside the living space INTO the attic through holes in the ceiling which are not usually sealed tight in a non-vented attic. Since the attic air is not circulating, it will tend to stratify and the hottest part will be near the ridge resulting in a warmer roof and melting resulting in the ice dams.

    Can you send some pictures? send to: pictures (at)

    Or call 800-595-8772 We can possibly help further with more info.


  7. I wanted to know which would be best for performance in my attic before I purchase the amount I need; I have a 1,800 Square Foot ranch style home. Is it better to staple the foil material on the Rafters or would it work best to lay it on top of blown in insulation, which is about 12" high?

    It really depends wether your PRIMARY goal is to reduce summer heat gain or reduce winter heat loss.
    For maximum summer benefit, you would staple it up, but for maximum winter benefit, you would lay it out.  If you don't have ducts in the attic, then laying it out is usually fine. Although it will reduce summer heat into the home, keep in mind that laying it over the insulation won't yield a cooler attic, just a cooler home.

    Or, you can do BOTH.  More info on The Best Radiant Barrier Install Method here:

  8. I'm still confused. I have a room with radiant water tubes in the flooring. Below this room is a craw-space which gets very warm from heat I'm loosing through the floor. I'm trying to figure out the best way to insulate between the joists in this crawl-space. I don't want to use fiberglass. Any suggestions? Thanks.

    It's really pretty simple to install radiant barrier for radiant floor tubing. Currently, the tubes are radiating heat 360 degrees both upward (where you want it) and downwards (where you don't want it). We want to DIRECT as much heat UPWARD as possible, This is done by stapling AtticFoil radiant barrier between the joists about an inch or two below the hot water tubes. The easy way is to cut pieces off the roll. If for example, you are on 16" centers, then cut pieces about 19" off the 48" roll. This will give you a bunch of 19" x 48" pieces. Then use a straight edge and create a "Tab" on one side about 2" tall. Staple it up on ONE side and then pull across the joist cavity and make a tab on the other side with your fingers and staple gun. You are basically going to do an install method similar to this video on How To Install Radiant Barrier In A Cathedral Ceiling using the "Tab" method except you will not need the foam furring strips and the fiberglass below is optional.

  9. Hi Ed! You site if fantastic. I have an unusual question regarding radiant barriers. I would like to use one to convert an interior closet to a wine cellar. I was thinking of adding 1" deep furs over the existing drywall and installing a radiant barrier on top to create the airspace. My goal is to keep the wine cellar about 10 degrees cooler than the house via a dedicated a/c unit inside the wine cellar that exhausts outside into a finished room. Everything I see talks about R value, but this design would be thousands of dollars cheaper and leave up the existing drywall. Any thoughts??

    I would not bother with a radiant barrier in an application like this.

    I would just bulk up the R-value of the wall by putting a layer of foam board - maybe 3/4" or 1" and then new sheetrock. Basically, you are trying to create a refrigerator inside your home.

    You really are not trying to get a huge difference (10 degrees) between the inside of the closet and the outside, so you just need to "move" some of the heat out of the closet and into the other part of the home. Yes, I think some type of a window unit will work OK considering the cost difference.

    Another challenge is that wine cellars are typically cold and WET, in order to keep the corks moist. A standard air conditioner will make it cold and DRY. I think this would really only make a significant difference if you were storing (expensive) wine for a long period of time. Newer wines typically use a synthetic corks (or screw tops) which are much less permeable to air and moisture transfer.

  10. I have an existing cathedral ceiling bonus room about 480 sq. feet. It looks like 2x8 rafters with at most R-19 insulation. It stays hot in summer and cold in the winter. Is there any radiant barrier matierial that can be installed on top of sheet rock that would help reduce the heat gain and loss? If not, any other cost effective material method to improve insulation? Thanks, Mac

    You have a couple of options.

    If the sheetrock is already installed, you can apply a radiant barrier, then use furring strips to create and air space and then another layer of sheetrock. Or, you could use 4x8 sheets of foamboard and apply it directly over the sheetrock and then another layer of sheetrock. Foil alone will help, but just won't look that great.

    If it's open and you have access, then your best method is to install it like in the 3rd video here: How To Install Radiant Barrier In a Cathedral Ceiling.

  11. Which product do you wrap the sealed ducts with? Thank you

    If you already have silver flex ducts, you already have a radiant barrier on your ductwork; an additional layer will not have much of an effect. If you have black, or grey ductwork, then adding a foil-covered duct blanket over the ductwork will help reduce radiant heat gain into the ducts.

  12. When using a radiant sheet in an attic, to provide insulation in both winter and summer, wouldn't an air gap be required on BOTH sides of the radiant sheet? In the summer, one wants to stop heat from transferring from the outside to the inside of the house; in the winter one wants to stop heat from transferring from the inside of the house to the outside. My second question is this: has any independent lab done tests of the effectiveness of radiant sheets under normal household conditions? All of the evidence I have found is subjective and anecdotal. I am wondering if the temperature of radiating surfaces under household conditions is really high enough to drive significant heat transfer through radiation. (I am a mechanical engineer and have had several courses in heat transfer, so I understand the basics.) Thanks, Frank Shaffer Pittsburgh, PA

    When using radiant barrier, an air gap is only required on one side of the foil because foil works off of TWO properties, reflectivity AND emissivity. The side that has a radiant heat source, an air gap and then the foil works off of reflectivity (the ability to REFLECT Radiant Energy back towards the source). Conversely, the side that has the radiant heat source, then the foil, then the air gap on the back side of the foil, works off of emissivity (the ability NOT to release (emit) heat). Therefore, an air gap is only required on one side of the foil.
    As far as testing goes on heat transfer through radiation, the relative percentage of heat loss/gain will, of course, vary tremendously depending on the age, type, and quality of your house and the climate zone it's in. Check out this article on Green Building Advisor for more information on this topic:

  13. I want to install the radiant barrier on top of my existing insulation in my attic. What do you recommend and where do I buy it?

    Probably the easiest method to install Radiant Barrier AtticFoil® is to lay the foil out OVER the existing insulation on the attic floor. You can Purchase AtticFoil® Radiant Barrier, which is the SAME product used by many professional installers and radiant barrier marketers, direct from and install it yourself.

    There are some pro’s & con’s to this method, so read the info on The Best Radiant Barrier Install Method BEFORE you make a final decision about which way you want to install it. Also, be sure and read the WARNINGS regarding installing foil directly over attic insulation in cold climates.

  14. Are there any possible fire hazards with a foil radiant barrier? What precautions should you take during installation to avoid electrifying the foil or connecting it to your homes electrical grounding system.

    We get questions about fire concerns from time to time, and understandably so. As with any product or building material in a home, care should be taken when installing the product to eliminate possible fire threats. That being said, we have actually known of many cases where a fire inside an attic was actually SLOWED down or smothered due to the fireproof quality of the layer of pure aluminum in the radiant barrier. When installing, it is important to stay clear of any sources of heat (such as a water heater) and give the foil several inches of clearance around these objects. Also, though it is possible, there is not really a simple and easy way to ground the foil, and realistically, if there were to be a fire in your attic, your whole house would technically be a "fire hazard."
    The best way to handle it is with proper, careful installation.

  15. I have a standing seam metal roof. I built the home about 3 years ago. It has a radiant heat barrier already applied from the factory on the sheeting. The hous has soffit vents and a ridge vent all the way across the top . It is a hip roof. No gable ends. My main trunk line for the HVAC (insulated) is in the attic. during the summer it sweats and cause condensation and stains the ceiling. I was thinking of putting in a powered static vent untill i read your site. What do you recommend? Thanks in advance Don

    There are two possibilities. One is that the insulation on the trunk line is either letting warm-moist air from the attic leak in and then it is condensing. The other option is that the insulation is not sufficient enough and the outer skin is too cold and is thereby causing condensation or it's leaking and blowing cold air INTO the insulation wrap and making it cold.

    Condensation ONLY occurs when relatively warm-moist air comes in contact with a cold surface. If you eliminate the warm-moist air or keep the surfaces warmer condensation will not occur.

    I'd focus on the ducts BEFORE doing anything else.

  16. Hi Ed, Thanks for all the great answers. I have a clean, 30" crawl space w/fiberglass insulation between the floor joists. Some of the glass is falling down and some of our floors are cold in the winter (especially tile in the bathrooms). I was thinking about having the glass removed and open cell foam sprayed in. A contractor offered to do the job w/closed cell for $3,400, including removing all the glass. I have about 1,500 sq ft of crawl space. What do you think?

    I would look in to completely sealing the crawl space below the home and basically making it "semi-conditioned" space. This creates both a moisture barrier on the dirt and a thermal barrier on the perimeter walls.

  17. Hi Ed, we are about to replace our roof and was quoted for Polaralum. Our house has a large roofline (long one story) and has vaulted ceilings. In the only accessible parts of the attic we have tresses that make it very difficult to reach the rafters. Polaralum looks like our only option for any heat barrier. What do you think? Are there any other options than Polaralum? It is a $3,500 additional cost and is so expensive that we don't know if the savings would justify the cost. Thank you, Stephanie

    I would not install ANY foil faced product without an air space. By definition you will not/cannot have a "radiant barrier." For more information, check out this website page: why radiant barrier will NOT work without an air space.

  18. Ed, I found your site by researching radiant barrier idea, after wife tried to impress with eShield offered by Costco. Two questions I have: (1) I could understand if the reflective layer was installed on the surface of the roof, so it would reflect the rays out. But if it's reflected already inside the home, then, I think, whatever heat is reflected, still stays inside, because once it's reflected, it simply hits another surface within the same home. So even if some part of the home becomes colder, by law of energy conservation, another part must become hotter by the same amount. Am I wrong? (2) could you give some references of the people who are using your product? we live in the suburb of Chicago.

    Yes, you are incorrect. We are keeping the insulation cooler; the insulation is your "thermal envelope" where all the heat gain/loss occurs ACROSS this assembly. If we can keep the insulation cooler, we drop the delta T and reduce heat flow. The roof is usually NOT part of the thermal envelope. So it may go up a few degrees. This is heat that WOULD have been absorbed y the insulation. With a radiant barrier, much of this heat that would have been absorbed by the insulation is re-directed into the atmosphere. This is like putting a West facing wall in the shade. The air temperature may not change but the outer wall temperature will be lower which will reduce heat flow into the structure.

    Due to privacy concerns, we do not give out references. Here are over 500 customer reviews:

  19. Hi Ed, I was slightly overwhelmed with the amount of information available here. I have a question to ask you though. I recently (Oct. 2010) bought a 1700 sq. ft. house built in 1976 and it seems to me that it is severely underinsulated. Over the winter, I never kept it too hot (60F), but my gas bill was around $150. Now in hot St.Louis summer my AC runs pretty much non-stop with setting at 76F. I checked my attic, which is crawl-type, and found that all I got there is about 3.75-4" of fiberglass roll insulation. On top of that, since it is a spit-level, I got no attic fan over my kitchen/garage area. I really would like to insulate it before next winter hits, and your suggestions on the most cost-efficient way to do so will be much appreciated. Thank you in advance.

    Have you had a chance to look at Energy Star's recommended levels of insulation for your area?
    I ask because oftentimes customers don't realize that adding a radiant barrier makes your traditional insulation more effective and they find that after installing a radiant barrier they don't need to add more insulation. I'm not saying this is true for you, but it is something to consider.
    Furthermore, it sounds like you could use a radiant barrier up there; however, radiant barrier does NOT take the place of traditional insulation (fiberglass, cellulose, etc.). Traditional attic insulation has R-value. This works to slow conductive heat. Radiant barriers reflect Radiant Heat. BOTH types of heat are trying to enter your home on a hot, summer day. The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the attic insulation. Then, the heat transfer method switches from radiant heat to conductive heat to move through the attic insulation and into your home. This is why you need BOTH Types of insulation. Traditional attic insulation and radiant barrier work together and each do their part. Radiant barrier is your first line of defense (against radiant heat) and traditional attic insulation (fiberglass or cellulose) is the second line of defense against conductive heat gain.

  20. I'm building a cabin in Ohio which I am stick framing up on poured concrete piers about two feet above grade. The floor is 3/4 plywood. I'm considering applying an insulating board over the plywood followed by another layer of 3/4 plywood and 3/4 hardwood floor. I fear insulating the exposed underside of the floor joists with fiberglass would invite mice,etc. I intend to heat with a woodburner. Any advice would be appreciated.

    You want something "solid" on all exterior surfaces. Yes, critters would love it. Unless you close it up, your only option is to thicken up the floor/subfloor by adding foam board.

  21. Ed, I'm installing a radiant barrier in my home between the rafters under my roof. I understand there must be a air gap for the radiant barrier to work, but how do I get to the area of the roof near the eaves? Should the radiant barrier seal against the rafters(trusses) or is the gap supposed to channel the air out? The videos do not show what to do with the ends, only the sides.

    Ideally you want about 3 to 6 inches of space at the top and 3 to 6 inches of space at the bottom. Attic ventilation is simple: you have holes in the bottom of your attic, and holes in the top. The goal is to install the radiant barrier in such a way that it doesn’t change the attic ventilation from its natural course.

    Check out this video for more information on air gaps: Leaving Gaps in Radiant Barrier Installation for Ventilation

  22. Ed, Small world Joe Shannon here Found you doing searches on RB systems and such. I am building a small cabin and we already framed it and used tech shield reliant barrier decking. I now I need at least 3/4" spacing for air flow. What product do you recommend for this before we insulate? Thanks for response and great to see your doing well. Been years since I had a good pizza!! :-)

    Hey Joe! Good to hear from ya! For this project am I right to assume it will be a cathedral ceiling, meaning the ceiling will share space with the roofline? If so, take a look at the THIRD video on this page:

    It will show you how to use foam spacers to do that. Obviously you will have some contact with the foil, but a little bit will be ok. Then I'd suggest laying foam board in the cavities, across the spacers, to have a flat surface - you could then lay more foam board on top, use spray foam, or go with traditional batt insulation. So long as that air gap is not compromised, you're going to be good to go!

  23. I have a 24 x 30 metal building. I have a 26 gauge metal roof that is screwed directly to 4" see purlins. There is no insulation and I am getting slot of radiant heat from the sun. What is my best alternative I can do to stop this? Should I have it sprayed with closed cell foam or some type of radiant barrier? Thanks

    If the structure is non-conditioned, then there is really nothing BETTER than radiant barrier to keep it cool. Basically, you are looking for shade from the HEAT. I've had many customers do garages, barns, sheds, porches, airplane hangers, warehouses etc. with GREAT results in comfort.

  24. Ed - I have an off-grid post frame salt box cabin with a light colored metal roof, and an upstairs living quarters. It gets hot upstairs in the summer in Indiana. The builders put a sheet of "wax paper" underneath the metal roof, supposedly for condensation control. There are no vents in the roof. Are radiant heat barriers better than conventional insulation? The rafters supporting the roof/purlins are 2x6" on 24" centers. Many thanks.

    "Are radiant barriers better than conventional insulation?" - that's tough to answer because it's like asking me "Are oranges better than apples?" It depends what your goal is! Radiant barrier does NOT take the place of traditional insulation (fiberglass, cellulose, etc.). Traditional attic insulation has R-value; this works to slow conductive heat. Radiant barriers reflect up to 97% of radiant heat. BOTH types of heat are trying to enter your home on a hot, summer day (or leave your home in the wintertime). The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the attic insulation. Then, the heat transfer method switches from radiant heat to conductive heat to move through the attic insulation and into your home. This is why you need BOTH Types of insulation. Traditional attic insulation and radiant barrier work TOGETHER and each do their part. Radiant barrier is your first line of defense (against radiant heat) and traditional attic insulation (fiberglass or cellulose) is the second line of defense against conductive heat gain.
    Hope that helps.

  25. Hi Ed ...I'm building a new structure. It'll have a totally open cathedral ceiling(4:12)pitch with 2x8 rafters. I live in British Columbia Canada and this is a get-a-way cabin in the skiing colder mountain region(3' of roof snow load). What I need to know in watching your 3rd video on cathedral ceiling installation, will 2x8" be enough and will R-17 be enough with the radiant barrier? Once installed like you have shown, I'll be installing cedar planks for a final finish, will I need to use a poly vapor barrier too or will this cause condensation? Please kindly explain the steps where you stopped in the video with the fiberglass application. (1)Ventilation channel. (2)Radiant Barrier (3)Fiberglass (4)??? (5)Finishing cedar planks. Thank-you very much. Paul

    Step #4 would be to attach the finishing material - that can be sheet rock, cedar planks, etc. In the Cathedral Ceiling installation method the air inside the assembly is not vented/ dead air; there is no risk or damage from "holding" the hot air in the wall. As far as insulation levels, that is region specific, but I'd take a look here and see what the recommended levels for your area are:
    Hope that answers your questions!

  26. Should a radiant barrier be installed under shingles on a new roof? Does the radiant barrier work better than the black felt that typically goes down under the shingles? Thanks.

    No, a radiant barrier should NEVER be installed directly under shingles. Radiant Heat by definition is heat that travels as RADIATION in waves across either a void (air gap) or vacuum - so if there is no air gap (in the case of putting it directly under the shingles) then radiant heat doesn't exist, and therefore a radiant barrier is useless. It will NOT work. Because aluminum is unique in that it is both reflective and very conductive, if it is not set up to reflect radiant heat, it will actually conduct the heat VERY well into the home. You must have an air space on at least ONE side of the foil for it to work. The only way this could work would be if there was a built-in air gap, as is the case with the majority of metal roofs and curved tile roofs.

  27. Hi Ed, I have a closet upstairs that does not have access thru the attic, it's facing the downside of the angled roof so basically is the roof on top of the closet ceiling and it gets very hot. As it is a closet and nobody looks at the small ceiling of it I was thinking of stapling radiant barrier from the inside of the drywall. Would it work? Is there another way to do it? Thank you Ricardo

    Yes, this would work. Ideally the goal is to get the radiant barrier closest to the source of radiant heat you are addressing, however since that would require ripping off your closet ceiling, that is really not worth the effort for a closet. You can attach it directly to the drywall, and just leave the foil open to the closet space. Keep in mind that if you touch the foil (eliminate the air gap by making contact) with your hand then it will be very warm, probably not as hot as an attic application, but still warm. However, the closet itself should be much more comfortable since the foil is only emitting 3% of the heat.

  28. New construction with foil backed 5/8 OSB roof decking over 2 x 8 rafters for a cathedral ceiling. Will the R-19 for 2x6 material work by providing the air space above the insulation? The roof will be a lighter shade metal with a full ridge vent and full 32" eave/soffit vent. I will also be using a conductive barrier added to the paint for the ceilings.

    No, insulation does not count as an air gap. It has to be a true air space - not an airy space, if that makes sense. You'd be best off using foam spacers to hold the foil off the roof in this case, if you need to add insulation to finish the space out into living space. Otherwise, if you are not making it into living space, then there is NO point in adding insulation up on the rafters - if doesn't belong there, it only belongs against a thermal envelope (living space).

  29. Hi Ed, Great site. I wish I had found it before starting our project. We recently had an insulation company evaluate our attic to better insulate our home. They recommended a combination of radiant barrier paint (which I now know is not as effective as the foil), foam boards with foil for our cathedral ceiling area and blow in insulation (R-30). As soon as they applied the radiant barrier paint and installed the foam boards - the temperature in the house increased by 10-15 degrees within hours! It seemed to push heat into the house. When we brought it to their attention - they had us install a whirly bird and a rigid vent and it made the house even hotter. They then redid our soffit vents (cut holes, installed new covers, opened them up because the rafters were blocked with old insulation). We even changed our AC ducts, return air, plenum and transition duct (they were old and ready to be changed in any case) to ensure there were no leaks. All to no avail. The house is still warmer and our AC now cycles every 5-10 mins and the compressor shuts off every single day. We've installed 2 window units as a temporary measure and are adding a third just to survive the heat. We are at a loss as to what may be causing it and we've lost confidence in our contractor's ability to remedy it. Do you have any ideas on what may be causing this reverse effect and warming the house despite the added insulation and venting?

    Wow - that is a lot going on! First, I feel like I need to make sure there is clarity between the DIFFERENCE between air temperatures and surface temperatures, especially since it seems the remedies are all related to AIR temperatures (ie. soffit vents, etc.).

    The actual air temperature in an attic is mostly determined by attic ventilation. The more air, the closer the AIR temp inside your attic will get to "outside" air temp (also known as ambient temperature). Then, in addition to lowering the attic AIR temperature, you also want to lower the SURFACE temperatures in your attic - this is where a radiant barrier comes in. You can lower the air temps all day long, but if the top SURFACE of that insulation is still hot, your home will be HOT. Now, the paint is very hard to regulate and maintain quality control, so there is no telling how much radiant heat it is actually blocking (if any), though even in the absolute best case scenario, it won't be more than 74% (and that is in perfect lab-testing conditions).

    Take a look at this video I did and hopefully it will help drive this point across:

    As far as why the temperatures went UP - that is something I can't address with certainty until I know first HOW they installed the material. For example, if they installed the foil-faced foam board in the cathedral ceiling with no air gap on the foil side, then of course it is not going to work. In fact, if that is the case, it will work AGAINST you because although radiant barrier foil is a great reflector of radiant barrier, when it is installed without an air gap (ie. set up for conductive heat flow, not radiant heat flow) aluminum becomes an excellent conductor of heat and promotes heat transfer. This is why it is SO crucial to make sure this is installed the correct way. I would contact them and get some more information about how they installed the materials and ask them what they determine the problem to be. If you need more references, feel free to point them to the site for install instructions and articles about radiant heat and the proper air gaps needed.

    Hope that helps!

  30. My builder has used TechShield on my new home. The problem is that this is supposed to be an encapsulated attic with spray foam insulation applied to the underside of the roof. Can open cell spray foam be applied and will it adhere to TechShield?

    No, radiant barrier roof decking does not work with spray foam insulation sprayed on to it. You have to have an air gap next to the radiant barrier. If you spray foam insulation right on the radiant barrier, you've wasted your money on it. Heat will conduct right through the radiant barrier because generally, materials with low emissivity have high conductivity.

  31. my building supply is reccomending radiant barrier roof sheathing by GP. i don't see how this product can work without an air gap to reflect the external heat. am i correct?

    Without an air gap on at least one side of the foil, you are right - it will not work. Now in the case of foil-faced roof decking, where the foil faces the inside of the attic on the bottom side of the deck, this works because the attic space is the air space. You are correct by suggesting the foil will not REFLECT the radiant heat, because with the airgap on the opposite side of the foil than the radiant heat source, the foil is NOT reflecting, however it is still stopping heat gain. It does this via a property called emissivity. Emissivity is the ability of an element/object to not allow heat to pass through. Therefore, radiant barrier decking (when installed properly) does work.

  32. Ed, thanks for your commitment to this subject. I haven't seen this topic so I apologize if you have addressed. I am completely redoing a vintage airstream, it's been gutted down to the shell. As you know, the exterior is all aluminum with aluminum ribs. The ribs are 11/2", I am looking for the best insulation system for the walls/ceiling and the floor as well. I do not want to use fiberglass as moisture and varments are a concern- and needless to say not effective in the small cavity. I've read forums where products like Prodex have been used w/ 3/4" foam strip spacers suspending the Prodex in the middle of the cavity. Others have used spray foam, foam panels, and of course fiberglass. I also have the option, since I'm replacing the interior aluminum skins, I can install an insulation layer outside of the ribs to combat the conductive nature of the aluminum. Your thoughts? Budget is a real concern eliminating the spray foam. I also have the floor to consider- your thoughts are greatly appreciated.

    The best installation method for walls, floors, vaulted ceilings (they are all the same in terms of layers) is the cathedral ceiling method. You want the foil closest to the outside if your goal is heat rejection, or closest to the inside if your goal is heat retention.

    It does not have to be complicated - it's really quite simple. Watch the video on this page:

    If you want a bigger bang for the buck, use foam board instead of fiberglass for the insulation in the stud cavities; while it's not as optimum as spray foam, it's still a great product.

  33. Hi Ed, My home is in central Florida and has a fiberglass shingled roof. I have a continious ridge vent, 2' perferrated soffit for ventilation and R-19 insulation. I am planning to re-roof the house with a metal roof and just read your article regarding under shingle ventilation. First, thanks for the information, as I was also considering double bubble foil insulation under the metal. I was already dubious regarding it's effectiveness, your article confirmed what I suspected. I have two questions. The first is, other than felt, is there a product you would recommend for under the metal that would make it be more energy effecient? My other question is, if I leave the shingles will they provide a positive degree of insulation or will it act to conduct the heat of the metal roof into my attic? I plan to use the galv/alum colored metal roofing in order to reflect heat away from the house. Thanks, Frank

    You need to add a radiant barrier under your new metal roof - nothing else will give you 97% reflectivity and as long as you get the air gap that is required, you will see great results. Have you seen this video I did on Installing Radiant Barrier Under a Metal Roof? Check it out, it will be the best thing you can add to your roof at this point - the foil will block the 97% and the rest that gets through the foil will travel conductively through the roofing materials below the foil and in to the attic.

  34. I live in an old, huge farmhouse..4 bedrooms upstairs. We close off the upstairs in the winter time but it's still very costly to heat. Is there any way to insulate the ceiling downstairs to keep the downstairs warm? What would you recommend?

    Yes, if you add a radiant barrier to the downstairs ceiling, then any heat trying to escape that floor through the ceiling will be blocked and forced to stay in the rooms below the foil. This is an effective way to keep the downstairs warmer in winter months. You could also add a radiant barrier BELOW the downstairs floor if you are losing heat through the floor as well.

  35. Will the product keep people from the drive by attempts to steal and or hack into a person's computer system to steal passwords and other data due to the aluminum and reflectivity nature of the product?

    I haven't heard of people using AtticFoil for this purpose, but it is made with pure aluminum. So if aluminum would work to achieve this, then it's more than likely AtticFoil will too.

  36. Sir Ed! I have installed a radiant barrier on the trusses. Would it help to put some on the attic floor as well? And if so what brand would be the best? Please give me your opinion on this Solar shield radiant barrier, thank you for all your time and dedication to this topic. You help many people with your advice.

    Yes, there are plenty of people who use radiant barrier foil on both the rafters (or trusses) and on the floor; they do this to set themselves up for the best results year round. Try - we have the best pricing and the customer reviews are amazing.

  37. We had a radiant barrier installed in April. When we had our systems (1 central air and 1 heat pump) serviced last week it was discovered that both systems had freon leaks in the indoor coil. Is it possible that the radiant barrier could change the air flow that it might be the cause of our leaks? Note that both systems are 12 years old.

    No, a radiant barrier would have no bearing on the mechanical operations of the HVAC units. The only main effect radiant barrier has on HVAC units housed in the attic is that it lowers their surface temps (meaning they are cooler to the touch than they otherwise would be) and this is actually beneficial since it allows the units to be more effective without working harder. 12 years isn't an unreasonable life span for a unit - it might just have been time to replace them!

  38. ok we all know that radiant barrier's are great. however, what type of insulation do you recommend IN ADDITION to using radiant barrier? Example, foam, batt, blow in, etc.. ?

    This is a complex questions because it really all depends on the home and at what point in construction the process is in. I'm an advocate for all the types you mentioned (foam, batt, cellulose, etc.) so long as they are used for the right purpose and under the right conditions. Foam is typically a more expensive option, but it also offers you a benefit the other kinds do not: it makes an air tight space. The others are easy DIY options and still offer great results slowing down conductive heat flow. I definitely do NOT recommend replacing insulation with a radiant barrier, because one does not replace the other. Rather, depending on the situation, you need both - one to address radiant heat flow and the other to address conductive heat flow. Together they go a long way toward making a comfortable home and a more energy efficient home.

  39. I'm thinking of building a new home in the spring down in Conroe Tx - 44 mi north of Houston. I have been talking to a builder that likes to use spray foam on the entire envelope. From what I've been reading I would like to do closed cell on the exterior walls and open cell on the roof rafters. I think down in that area it's cooling that's the problem, not heating. I'll use open cell on the roof as a leak will show up and the open cell will allow it to show up. Do I need a radiant barrier on the roof - the type that's seal to the plywood and you buy the plywood that way . Can you still spray open cell foam right up against the radiant barrier or don't I need it at all in this type of application? Do I need a vapor barrier on my ceiling before the sheetrock gets put up??

    Yes, you can use spray foam in conjunction with radiant barrier foil; however, you MUST have an air gap, even if you are using spray foam insulation. As long as you can get an air gap, the foil will work; if you plan on rejecting heat gain, then the foil needs to be closer to the outside, again with the proper air gap.
    About the vapor barrier, yes - you will need to place some type of vapor barrier between the attic and the living area, but take caution to only have ONE vapor barrier in this assembly. More than one introduces the potential for trapping moisture which, as you might know, we never want to do.

  40. Ed,Do you have any information on your website about insulating knee walls and dormers? I have a Cape Cod style home with fiberglass batts that won't stay up in the knee wall areas. I know I have to address this issue before I can install drywall. Would it be a good idea to back the fiberglass with rigid foamboard insulation to give it stability? How would a radiant barrier be best installed in this situation. I would like this area to be available for storage. Am I correct in thinking that I need the foam channels to direct airflow from the soffit to the ridge vent in this kind of application, whether this area is conditioned or unconditioned if I decide not to finish it for storage space. Any advice would be most appreciated! Thank you!

    Right now I do not have any information posted on the website about this application (though I am working on that) but it's going to be just like a Cathedral Ceiling installation. You can cover the insulation around the backside (attic side) of the knee walls with the foil to block radiant heat from being absorbed by the insulation, and ultimately the room. If you REALLY want to insulate it, then yes, add foam board between the wall studs. Basically it will go like this from the attic side coming in toward the room:
    1. Roof Deck
    2. Air Gap (created by foam spacers)
    3. Radiant Barrier Foil
    4. Batt Insulation
    5. Foam Board
    6. Drywall/Sheet Rock
    There is a video of this method in progress here:
    Does that help?

  41. Why does our metal roof (residential) have open air space all along the roof line at the peak?

    I'm not sure but it sounds like that is where the ridge cap is supposed to go, so if it is open it sounds like the roof cap is missing. I recommend you contact your roofer about this question.

  42. Help!!! Can I lay plywood over my attic radiant barrier?? We unfortunately had a very bad company charge thousands to do a bad job and I want to correct it.

    The simple answer is NO. Radiant Heat, by definition, is heat that travels as RADIATION in waves across either a void (air gap) or vacuum - so if there is no air gap (in the case of putting it directly under the shingles) then radiant heat doesn't exist, and therefore a radiant barrier is useless. It will NOT work. Because aluminum is unique in that it is both reflective and very conductive, if it is not set up to reflect radiant heat, it will actually conduct the heat VERY well into the home. The only way you can get foil up on the roof is if you have an air gap (you can use battens to achieve this) or you can install it on the bottom side of the roof deck, with the foil facing down, toward the attic space.

  43. Re a re-roof job - we have 1x6's boards now with 1x6 spacing between those boards. Plan is to install radiant barrier 4x8 sheets over those once all shingles are removed, and then to re-shingle. You have repeatedly said radiant barrier requires air space to be effective but we will be losing some of that air space given that there are boards, gaps, boards, gaps etc. Suggestions?

    Thermal bypass (meaning the heat is still moving through the objects that are not covered with radiant barrier and then radiating heat into the space) will occur any place there is full contact. However, the areas where there IS an air gap will still be effective.

  44. I have searched but not found anything. How does your product with regards to emf? Will it do anything to mitigate emf Thanks Mike

    I have heard of customers using it to stop emf (electromagnetic fields) or a SCIF barrier, but I can't offer any advice/guarantees on this topic/use since it is not the intended use for AtticFoil.

    The only way to know for sure would be for you/customers to test the use yourself.

  45. Regarding installing foil to rafters with staples to rafters. Doesn't this make the foil that touches the rafters conductive therefore lessening the effect? I guess nothing is perfect, but the price of the product coupled with the easy of installation is the best and easiest way. Although tweaks could be made, it would come at great expense of time and resources to try and alleviate a small problem.

    This still works because the foil uses its emissivity property to block the heat from emitting. The reason this works is because the side of the foil facing down toward the attic has the attic as its air space.

  46. Hello, I first want to say I appreciate this website. I am in the process of building my home. It is a single story home but I have plans to create an upstairs space under the roofline. I was considering the roof sheating with radiant barrier foil on the underside. From reviewing several posts here I believe this will work as long as there is a proper air gap. Normallythere would be plenty of air space between the foil and the insulation but in my case a portion of the upstairs ceiling will have to follow the roof line. In this case with 2x6 rafters I will barely have room to install a 2" air gap filler baffel (to continue attic space air flow up to the ridge vent)and the insulation. So there would not be any air gap. I am trying to think of a couple options. Install a second 2x6 below the first one (at least for this section) to create 12" of space then I could install 6" of insulation and for r-33 and still have 6" of air gap. Do you think this would work the way I am describing or am I misunderstanding how this all works or is there just a better way. Also I am wondering if I should use radiant barrier roll sheets stapled along the bottomside of the rafters in conjunction with the foil sheating. Do you think theyu would work well together or would they work against each other. Thanks for you help. John Parks Louisiana

    Your first option (creating the 6" air gap would work fine, but keep in mind you will be losing roof clearance for the room below. The best way to install the foil in the cathedral ceiling application is shown on this page:
    As long as an air gap is achieved and there is a source of radiant heat, the foil will work. Ventilation is certainly an important component in the construction of a house, but is by no means the cure all for the hot summers
    Another option is to do what I've done on my new home. I used my new radiant barrier house wrap product; with the newer wall systems tyvek is really not needed anymore. However, if you have brick or stone catching sun, getting a radiant barrier to the outside of the wall can significantly reduce heat flow. I did a double-decked ventilated roof OVER a full foam encapsulated home; I used 2 x 6 advanced framing and then the DOS sis board and then another 1/2 foam to the outside before the AtticFoil house wrap. It works wonderfully!

  47. Can I put the radiant barrier on the face of my wall studs, over batt insulation, before I hang the sheetrock? Exterior has 1/2 inch OSB with Tyvek. Thanks, Keith

    No, generally this will not work. You cannot "sandwich" the foil between the drywall and the insulation. You MUST have an airspace on ONE side.

    Radiant heat by definition is heat transfer by NON CONTACT ACROSS an AIR SPACE. Without an airspace, you cannot even have radiant heat. If you have no radiant heat, then you cannot by definition have a radiant barrier. This is similar to why you cannot get a radiant barrier by putting foil directly under shingles.

  48. Thanks for the great site. I've seen discussions on the internet that state that foil based radiant barriers will not meet 2012 ASTM Code 2599 for fire safety tests. I'm not sure if this is accurate or if this is just claims by competing products. Can you expound on this? Thanks!

    Just FYI ASTM 2599 is not a code, it's a mounting method. It's a method that the foil must be mounted according to when it is being tested for burn characteristics. For more information on the fire code "hype" check out this page:
    I also recommend you go to the actual ASTM page and read what the standards test for, you'd be surprised how companies can twist and turn their words to be in their favor.

  49. Hey I am a basic home owner, and had some attic ventalation there a way to call you?

    You can call us at, go to the website and under the contact us page you will find a phone number.

  50. I saw your video on radiant heat. Thank you, it was very helpful. I have a flat roof. I was thinking of laying a plywood layer with silver. That does not seem appropiate now. Are you familiar with any roof coating that works?

    Yes, DuroLast makes a great cool roof system. Check them out online:

  51. Hello I have a 34x40x12 pole barn with truss roof is 6/12 with 12 in. overhang roof is metal black felt screwed to osb board.I am planning to use 4x8x1/2 foil faced on ceiling @ 12ft.Which insulation would be best on walls? prodex 10 seems to have the best r factor but will there be a moisture factor at the floor or do I need to leave a air space between ext. metal and foil.Exterior metal is ribbed. Spray foam would probably be cheaper and faster to install will there be a moisture problem with the humidity in indianapolis.I want it insulated well for winter.Thanks Dennis

    In regards to moisture, keep in mind that a radiant barrier or insulation doesn't cause moisture, moisture causes moisture. Ideally you'd want some sort of ventilation around the install so moisture can flow freely and evaporate; the basic overall idea is to install the foil in such as if it's not even there (in terms of airflow). That being said, either Prodex or spray foam will work but if the barn is not being conditioned then you don't need the R-value; R-value is for conductive heat loss and on a non-conditioned structure you don't use traditional insulation because there is nothing better than radiant barrier to temper the heat gain. Have you seen my page about installing foil in the walls of a barn too? It can be used on both the ceiling and the walls:

  52. Ed, my question basically relates to the effect of the TYPE of construction in an attic on cost and effectiveness of any radiant barrier product installed over ceiling joists and traditional thick insulation...also, to the relationship of type of construction to the "completeness"/"tightness" of the installation. Specifically, we have a one story home in Folsom, CA where it gets very hot in summer and relatively cold (for California) in winter. We have two HVAC units in the attic, many heat ducts, to work around, etc. But, what especially concerns me is that the 'stick-type' construction in the attic relies on many angled "purlins" running from the ceiling joists up to the rafters. If the RB needs to be carefully 'cut out' (around all 4 edges of each and every purlin) every place a purlin is attached to the ceiling joists, this would seem to introduce a lot of labor cost and many places where heat could otherwise pass. Is RB a practical installation alternative under these circumstances and is there any way to make an install by professionals easier/less costly but still not end up with swiss cheese? Thanks.

    The radiant barrier does not have to be "cut out carefully" around every purlin (do you mean rafter?). You can simply staple it across the bottom of the rafters in long sheets. If the trusses are in the way, then use a narrow product (like the 26" wide AtticFoil) and install it parallel with the rafters (vertically) so there is less cutting and so the rafter/truss ends are covered. Remember, it doesn't have to look pretty to work - you just want to cover as much as you can without blocking any intake or out-take vents. Does that help?

  53. I have a small area above a portico that is decked and can be used similar to an attic space. However, the only "ventilation" is a roof hawk on one side of the pitched roof section. There are zero soffit type vents for any type of air to come in to the "room". I want to make a storage area out of this space, but want to make it suitable for books and other things that need to survive the heat of Houston. My idea was to install radiant foil on the rafters and a small portable room A/C unit to keep it climatized. I don't intend to make it habitable; more like a larger closet that gets some of the interior cooling from the surrounding room air flow. Problem is, there wouldn't be any air flow across the barrier skin up 'n out a ridge vent or such. I was thinking to use the roof hawk as the outlet for the portable room A/C unit. Suggestions?

    If you are just looking at tempering the heat then you can just add a radiant barrier. However if you plan on cooling it with an A/C unit, the install gets more complicated. At that point you need to seal up the space air tight and also add both a radiant barrier AND traditional insulation. So depending on which way you go would make the difference between what you need to do. It'm my opinion that if it is just a storage area, then you can go with radiant barrier and proper ventilation (which may mean adding some soffit vents down low on the roofline of the portico area).

  54. would attic foil work with floor heating. Running the foil across the joists to heat the joist cavities?

    Yes - for more information about radiant heat flooring and radiant barrier check out this page with photos and more info:

  55. Hi there! I have a 1100 sq ft bungalow that was built in 1951. I live in montreal so hot summer cold winter. The attic soffits are closed and it had 2 small roof vents towards the middle. I did the roof in the fall and the roofer reccomended and installed 2 larger roof vents more evenly spaced. The plan this summer is to oen the soffits but I am concerned about messing up a moisture free 60 yr old attic. Should I do radiant barrier? Open soffits? Both? Thank you!


  56. how do you properly vent your attic on a hip roof when installing radiant barrier

    The attic ventilation stays the same, you just take precaution when installing radiant barrier so that the air has free and easy access to your exhausts. On hips and valleys this is done by simply cutting a hole or slit at the top and the bottom of each cavity. Air will naturally be drawn in the bottom and out the top. Take a look at this page for more information:

  57. We have adequate insulation on the floorvof our attic, but attic gets afternoon sun and gets very hot. We're having insulation added between ceiling rafters along with radiant barrier. Should faced or unfaced insulation be used? Thank you.

    Neither. Traditional insulation does NOT belong up on your roof rafters, it belongs on your attic floor against the thermal envelope (the areas you heat and cool). The only time this is recommended is if you are converting your attic space into a living space that you will heat and cool; otherwise leave the traditional insulation on the attic floor and get the radiant barrier up on the rafters.

  58. Just had a metal roof installed last year. Had a storm with 60 mph winds and it blew rain water into my attic under the ridge vent into the attic. The ridge vent has this scotch bright material underneath to prevent water from going into the attic but it didn't work. Is there something better that could be put under the ridge vent to prevent this from happening again ? Thanks for your time. Tom Howard

    Baffled ridge vents are the way to go. They will cause the wind and rain to be deflected over the ridge. Other than that, I cannot think of a good solution.

  59. We are a wine store and we would like to place a wine rack against a set of windows. We are in a very temperate area so extreme heat is not an issue. What would you recommend we do to insulate the windows from direct sun. We have considered Reflectix or rigid foam clad in plywood (to make it look presentable). Thank you.

    Yes, I would use some type of foam board and seal it up. The more reflective the outside (facing the sun) the better. Foil is best, just being white is fine or you you could make it black if you need it to be black. Really, by adding insulation you are turning the window into a wall. Anything will work as long as it looks nice enough for you.

  60. is it wise to have a radiant barrier installed over existing ceiling insulation and have it stapled to roof rafters also?

    I know many people who have the time and energy to do both methods and see good results. Though it is not essential to do both in order to see a vast improvement, doing both methods will yield the best possible results year round.

  61. I am building a new wood framed structure in the California desert with a cathedral ceiling: 2x10 rafters with R-30 fiberglass insulation, covered with 1/2" plywood roof sheeting. On top of the roof sheathing will be 15# felt and then 1x4 furr strips on which we will put a metal roof. Where is the best place for the perforated radiant barrier? Would it be alright on top of the felt and under the furr strips (the furr strips would provide the air space between the radiant barrier and the metal)? Thanks for all your wonderful info!

    Yes, this is a great application for radiant barrier. You will want to put the foil just below the airspace. Here is a page on installing Radiant Barrier under metal and tile roofs.

  62. I have a single gabled home with 6 on 12 pitch. The house has continuous soffit vents, gable vents, and a continuous ridge vent. I am going to add blown insulation and was considering adding a radiant perforated foil barrier on the rafters - hot/humid climate. Does the foil have to go all the way up the rafters. Will half way up the rafters still be an improvement?

    The answer is yes. Radiant barrier is like shade (shade from the heat, not so much the light) and foil insulation has a cumulative effect: the more coverage you get the better your overall results. The majority of our customers get somewhere between 70-90% of their attic covered. Our advice to you is to install as much as you can, as fast as you can and don't worry about the last little bit you can't get to; any coverage is a step up from no coverage. As you increase coverage, you increase comfort and effectiveness.

  63. I just had radiant barrier installed and noticed a gap in coverage (probably a good 12 inches). The gap is more than half way down the the roof. I thought it should be solid coverage.

    Partial coverage with radiant barrier works - so the more you cover the better but getting some coverage is better than none at all. A gap of about 12 inches is typically nothing to worry about - most gaps at the peak or base average between 3 and 12 inches. Obviously the more you can cover the better, but a small gap is not going to drastically alter your results. For more information, check out this article and video here: Does Partial Coverage with Radiant Barrier Work?

  64. Ed, I just bought a cape cod and I am considering adding insulation in the attic as well as a radiant barrier. I plan on doing most of the work myself, however a contractor has tried to sell me "e-shield" radiant barrier for the hard to reach space between the kneewall and the flat ceiling (where there is about 3.5" of insulation between my bedroom and the hot roof). Apparently his guys have a special tool that can accomplish this. I am skeptical about this because I've learned that radiant barriers must face a ventilated airspace. Would e-shield or any other radiant barrier actually be effective in the concealed space between the upper and lower attics of a cape cod, where there is no ventilation? I have soffit vents, gable vents, and rooftop vents, but I am not sure if there is an air space between the insulation and the roof in this tight area. Your thoughts?

    Ventilation is not required for the product to work. Ventilation helps address the air temperature and promotes drying out of moisture but even though those two things are important, they are not related to the effectiveness of the radiant barrier blocking heat. Regardless of your ventilation, the foil will still work to block 97% of radiant heat attempting to enter the home as long as when you install it there is an air gap (at minimum you need about 1/2 to 3/2 of an inch) on at least one side of the foil.

  65. If I can only access to a portion of my attic rafters to install a radiant barrier is it worthwhile to do a partial install that covers only half of the rafter space that I can access and leave the less unchanged, or is it necessary to have complete coverage to generate any benefit? Thanks, Brian

    Partial coverage with radiant barrier works - so the more you cover the better but getting some coverage is better than none at all. For more information, check out this article and video here: Does Partial Coverage with Radiant Barrier Work?

  66. I have a shake roof and am getting ready to have solar put on to a portion of my roof that face the sun. They will have to reroof the sections where the solar panels will be installed due to code here in Bakersfield California. The areas where it will have to be reroofed are vaulted ceilings in my home. The rafters are 2x6 and insulated. Do I need to have all the 1x6 slats removed under the shake and have the radiant barrier plywood installed right to the joists or can I have the radiant plywood installed over the 1x6? Is the R factor going to change that much? Please let me know. Thank You Paul

    You can install it in either place - as long as the radiant barrier is facing an OPEN AIR GAP. There needs to be at least 3/4" of space between the foil and any other object - this includes insulation. You cannot sandwich the foil between insulation and plywood - it will NOT work. Also, radiant barrier does not have an r-value on its own - r-value is attributed to materials that address CONDUCTIVE heat flow, while radiant barriers address RADIANT heat flow (two different types of heat).

  67. I am having a townhome built and requested radiant heat barrier be installed. After walking through the unfinished home today I noticed the attic/bedroom upstairs was considerably hotter than the downstairs. I walked through other similar units being built without radiant barrier and did not notice the same temperature difference. It seems this product is new to this area and I don't know how to check that the work is being done to accomplish a cooler home in the summer. What can you suggest?

    Go up into the attic space and take a look at where the barrier is installed. What region/state are you located in? If you want, you can email me photos of the install at support@atticfoil(dot)com and I can offer you suggestions based on the installation.

  68. I installed a radiant barrier in my garage. If I leave the 3 inch gap at the top and bottom could I place drywall directly against the radiant barrier or do I have to create another space between the radiant barrier and the drywall?

    As long as the radiant barrier is double sided and there is an air gap on at least ONE side of the barrier, then you can attach the other side of the barrier to something without any issues.

  69. I have an uninsulated crawl space and want to install a radiant barrier without additional insulation to seal the bottom floor joists and reflect heat back into the house during the winter. Will this work or do I need to add more R-value?

    Because the application is below a conditioned space (the living space), you want to utilize both radiant barrier and traditional insulation. You can use foam board, spray foam or traditional batt insulation and a single layer of radiant barrier foil; you need R-value and reflectivity. You will get the best return on your investment if you buy the radiant barrier and the traditional insulation separately and then combine them yourself.
    If you do not already have a vapor barrier in the crawlspace, then you should choose the AtticFoil® Vapor Barrier Radiant Barrier product to get the double benefit of blocking moisture and retaining heat in the flooring.

  70. Guru, I have a commercial warehouse space in the southwest. It has conventional trusses with a smaller 2x4 top cord. These will remain exposed. I really would like to get your 2 cents of knowledge to manage the radiant temps? I was considering a 3.5" batt and stapling foil on the bottom of the "top cord". would there be a benefit to the foam fur strip then batting method? or combination of both? Maybe 3 layers? Or another option? Thanks in advance, Matt

    To manage radiant heat, your best option is going to be to get a radiant barrier up near that roofline, closest to the roofing as possible, while maintaining an air gap between the foil and the roofing. If this is a sealed and conditioned (A/C or heat) space, then you can also utilize batts or other traditional insulation, otherwise for a non-conditioned space, a radiant barrier is going to make the biggest impact. It's basically creating "shade" over the structure and preventing 97% of radiant heat from entering the roof.

  71. I have a house that I'm soon going to be finishing out the attic. I have 4 foot tall pony walls. I also have a metal roof that was installed over standard decking along with 15pound roofing paper but did not install a radiant barrier. I thought I would install a radiant barrier on the inside of the decking but the research I have done I think I would be wasting my time and money.It would be installed in this order: (1st) bottom of decking (2nd) layer of radiant barrier (3rd) air baffles (4th) blown in cellulose insulation (5th) finish ceiling material. As you can see there will zero air space. So my question is should I go to the trouble of installing a radiant barrier now or just skip it since there will be zero air space? I think the vertical pony walls would in fact benefit from the radiant barrier but not the pitched roof section. I hope this all makes sense the way I have explained it. thanks Mike

    It's not that complicated to introduce an air space - it will serve the purpose of the baffles, but still allow you to utilize a radiant barrier - which will help greatly. Have you had a chance to look at this website page that shows how to do this? How to Install Radiant Barrier in a Cathedral Ceiling.

    It has great info, including a video I did and customer photos, that show you how you can easily achieve the air gap and therefore use radiant barrier.

  72. I think a lot of heat gain occurs from the attic to the exposed sheet metal when the cold air return flows through the common plenum used for heating and cooling. Would it be beneficial to paint the sheet metal housing where the return air flows back into the heater / AC unit with paint that has a reflective additive? What about painting the heater plenum since the ac return air flows through it also? Would this create a fire hazard?

    I would not use a paint additive. All BARE metal should be wrapped pretty airtight and well insulated. If not airtight, warm moist air will find cold metal and condense.
    The metal boxes are probably insulated in the inside; I suggest you wrap the plenum - a regular duct/plenum wrap will achieve this.

  73. I have a home in Texas that has a foil shield on the underside of the roof decking. I am currently looking for ways to reduce energy cost by redoing ducts, blown insulation, etc. Is there any benefit in adding another radiant barrier like yours in my application?

    There is not going to be much of a benefit since radiant barrier decking work. The main down side to radiant barrier decking is that it doesn't take in to account thermal bypass on the rafters (meaning the heat is still moving through the rafter ends that are not covered with the board, and then radiates off the ends into the attic). Using AtticFoil across the rafter bottoms does not allow for thermal bridging, so if you want to add a second layer across the rafter bottoms, you could.
    Just keep in mind that you already have a radiant barrier up in your attic, so if you are still having trouble keeping the home cool, you might want to consider an energy audit to see if there are other factors at play that could be affecting the performance of the home.

  74. Hello, I recently had a re-roof and re-deck with radiant barrier attached to the decking. They installed the radiant barrier decking on to the existing slats not removed when they removed the cedar shake shingles. Should I paint the slats with radiant barrier paint; what would you recommend? The roofing company recommended leaving the slats, as they said it would provide more support, and that roof decking would never sag. My house is about 1500 sq. feet, and was built in 1958. should I consider somehow taking out some of the slats, if somehow possible; By the way, I live in the Dallas, TX area. Thank you for your thoughts.

    If the roofers that installed the roof recommend keeping the slats, then I'd recommend you listen to their advice. Sure there will be conductive heat flow where the slats touch the radiant barrier decking, but if the remainder of the decking is open to the air gap created by the slats, then you have foil performing in those areas. If you're really concerned about it, you could add an additional layer of foil in the attic space, though I think you will be fine with leaving it the way it is.

  75. Great information, Ed. Thank you; I learnt a lot. My question is along the lines of #31 (dead air space on only one side of radiant barrier) as it applies to garage doors: if I cut the radiant barrier material into 54"x22" rectangles and tape it to the panels of a metal garage door, will that cut radiant heat into garage? Ideally, I would buy the bubble foil material and make a bow out of these rectangles so that I get the air gap between the metal and bubble foil ... but if I get emmissive insulation from the double sided RB, can I do without the reflective insulation on the garage door side?

    Yes, if you add a radiant barrier to the garage door panels (that are catching sunlight) with the proper air gaps, then the foil will reflect 97% of that radiant heat back out the garage door. Keep in mind the roof above the garage can also bring heat in to the garage, so for maximum benefit, cover that area too.

  76. can i use foil insulation below an enclosed porch on top of the soil? it would be difficult to place plastic due to the lack of space i would have trying to lay it flat. it would be easier to place something more rigid that can be pushed on top of the soil. thanks dan

    The only reason for doing this would be to minimize heat loss through the porch floor. You could use the solid radiant barrier foil - it gives you both a vapor barrier and a radiant barrier in one:

  77. Hi. I've got a question about radiant barrier with NO attic. I'm building a house, 2 story. The whole second story is going to be living area. There is no attic. We've put the techsheild roof decking on. I've tried to find info on the space needed between the decking and the insulation but am coming up with nill. We've got 2x6 joists. We were planning on R19 insulation, but that would leave no space between the insulation and radiant barrier decking. I'm wondering if we should go down to R13, so there'd be a space. The roof is going to be tin. I'm in SE Texas, west of Houston. Any lead in the right direction would be greatly appreciated. Thanks!

    This is a simple cathedral ceiling application and it is VERY common. Details, including a step-by-step video can be found here:
    With Techshield, you can't really get the required air gap since there is a need for traditional insulation and they would press against the Techshield, rendering it useless. The best option if you want to utilize it would be to use the foam spacers and then perhaps foam board before filling with insulation. Call us for more info.

  78. Hello Guru, I live in my motorhome year round, Im from British columbia Canada, At present I have a skirting around the motorhome, this material is made from the same material that you see covering spare tires on the back of many vehicals, there is a pocket on the bottom that I have installed chain link, to help stop the wind from blowing it, I was wondering if there would be any benefit too install your product behind the skirting? Any offer of advice would be greatfull. Thank you

    Not really. If you are trying to stop heat loss from the floor into the ground below, the foil would work best attached to the bottom of the floor, as the last layer underneath the floor. Putting it on the skirt won't stop the heat from going into the ground below the home.


    Traditional insulation is not a thermal barrier, it simply SLOWS heat down. To STOP or BLOCK heat, you need a radiant barrier. The best way to tackle a cathedral ceiling is by installing a radiant barrier in your cathedral ceiling. You do this in addition to traditional insulation and the combination of the two is the best bang for the buck.

  80. If radiant barrier decking is installed such that the foil is in full contact with lathing without any air space, will this cause the attic to become an "oven" in hot climates? I see many inexperienced roofers doing this. I realize that the radiant properties are null and void, but what if any detrimental effects are there to the house?

    There isn't really much data on this - the radiant barrier does become null and since aluminum is a good conductor of heat it will in effect promote heat transfer from the roof into the home, but it is not really changing the amount of heat that enters, just how well it can enter.

  81. Hi! Is it okay to install a radiant barrier on a flat roof under a durolast roofing system? I look forward to hearing your expert resonse. Thanks!

    No, if the radiant barrier product is sandwiched between two materials then it will not work. In order for radiant heat to be present you must have an air space, so with no air space, the heat is not in radiant form. Just stick with the Durolast system on its own - it works well.

  82. I just bought a house in Miami with Gable style roof, shallow slope ans shingles. Attich spave is very tight, and very hot. Not sure it is ventilated, does have vents on Sofit, but have not seen vent end. Quastion, I wanted to install radiant barrier and maybe a new roof, so I though of putting radiant foil OVER the old shingles, then put new battens and put tiles or board and shingles. basically I would save in the removal of the old roof. Could I do it or is it a sloppy work?

    You can definitely do this! It's a very common way to incorporate radiant barrier when a new roof is being added over the old one. The battens give the required air gap and the foil offers full coverage - much easier than crawling around a tight attic space! Check out this page for step by step info and tips and photos:

  83. would a tekfoil bubble wrap product work over large window areas to reduce the heat loss especially at night when the solar gain is zero ?

    Yes, if the home is being heated from the inside then you have radiant heat. The foil will block out the light and the solar heat. However keep in mind that if the window is not sealed properly, this can be the main source of the heat loss. Leaking windows and doors waste a ton of energy and make those areas hard to keep comfortable.

  84. I will be building a house in the Houston Tx area. In this area unvented attics are the norm. This is usually accomplished with spray foam insulation applied directly to the underside of the roof decking. This eliminates the effectiveness of a radiant barrier decking material. I'm considering installing foil between the rafters 1" below the roof decking and then spray foam the remaining rafter space. The ends of the air gap would be sealed resulting in a sealed air space between the foil barrier and the roof decking over the majority of the roof area. Would this be an effective method or would it lead to other problems like extremely hot shingles? Thanks Ron

    The best way to incorporate spray foam and foil is to go with a Cathedral Ceiling method for the radiant barrier and then use foam board in between the rafter cavities and then fill the rest of the cavity with spray foam. The reason for the foam board is because the spray foam won't stick well to the foil but it will to the foam board.

  85. Ed, Thanks for the site, it seems helpful. I've been doing a lot of research on radiant barriers and heres the concensus I've come to: Radiant barriers make the most sense in poorly insulated buildings, and have less of an effect in well insulated buildings. Generally in warm/hot climates cooling an attic space is almost always desirable. I'm curious, what would your bottom line statement be for a radiant barrier in a cold climate? The general argument I see is that you're better off simply adding more R-value to the floor or roof joists (depending) to keep heat in and cold out or vice versa in the summer, than installing a radiant barrier.

    Ultimately it's all about surface temperatures. The larger the difference between the inside and outside surface temperature, the more heat will flow in or out.
    How does this relate to your attic insulation? You can add more attic insulation, and this is probably a good idea for most homes. The problem is that it can become too much of a good thing. Traditional attic insulation has R-value; this works to slow conductive heat. Regular fiberglass or cellulose attic insulation only slow down heat via conduction, they do not stop or block heat; they also tend to hold heat in.
    Radiant barriers reflect radiant heat.
    BOTH types of heat are trying to enter your home on a hot, sunny day (or in the winter heat is trying to escape your home to the cold outdoors). The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the attic insulation. Then, the heat transfer method switches from radiant heat to conductive heat to move through the attic insulation and into your home. This is why you need both types of insulation. Traditional attic insulation and radiant barrier work together and each do their part. Radiant barrier is your first line of defense (against radiant heat) and traditional attic insulation (fiberglass or cellulose) is the second line of defense against conductive heat gain.

  86. Hi Ed, Thank you for all your knowledge so far. So basically I am re-doing my bathroom and want to put a radiant barrier in the walls. i saw in your video how there needs to be an air gap on one side, so how would you suggest accomplishing this? I wanted to do spray foam/ fiberglass hybrid system that i have been seeing online, so then could I do the foam strips (like in the cathedral ceiling video) in a horizontal position way to create the gap? Or something along those lines? Any suggestions would be very helpful. Thanks

    I wouldn't recommend radiant barrier on internal walls between rooms. Is there a reason you are wanting to do that? Typically radiant barrier is the outermost layer - closest to the outside.
    The wall application is pretty straightforward - check out this page for photos and install instructions: How to Install Radiant Barrier in Walls.

  87. I am installing a metal roof that will be galvalume (no color) and quite reflective. This is new construction, and I am planning on using Tech shield OSB with foil side up, 2x2's for air space, and than 5/8"OSB to fasten metal roofing. Do I need another reflective barrier between air space and metal roofing

    Nope - the Techshield will do the job fine.

  88. Good morning, I am fixing to build a house and I want to maximize the amount of radiant heat that I reflect. The house will be built off the ground with a metal galvalume roof. 1) What would be your recommendation(s) for different options of radiant barrier on the roof? [whether it be to use the aluminum covered foam board or the aluminum-covered plywood. I wasn't sure what impact the tar/felt paper had with the radiant barrier] 2] Would you recommend radiant barrier on the outside walls? [I will be using Hardie planks for the siding] 3] Would you recommend using aluminum covered plywood to place on the bottom floor joists facing the ground? Thank YOU

    You have a couple options. You can go with plywood, tar paper and standard single sided perforated radiant barrier foil (the foil side would face UP toward the air gap created by the roof), or you can go with plywood and a solid foil material as your vapor barrier and radiant barrier in one. For house wrapping the home, please refer to this article: Adding a Radiant Barrier House Wrap Behind Siding.

    As far as other places for the radiant barrier (like outside walls) - basically any exterior wall that is catching sunlight will benefit from a radiant barrier. Remember, as long as ONE SIDE of the double sided foil is open to an air gap, then the foil is going to work to BLOCK 97% of RADIANT HEAT.

  89. I saw a roof go on the other day with a product called Solarhide applied foil facing down against the asphalt felt, under the shingles. What do you know or think about this?

    Here is an article I wrote on companies using "radiant barrier" directly under shingles or underlayments:

  90. I am building a new house and I am going to have the builder install LP Techshield. If you use LP Techshield, do still need to install a ridge vent? The roof on my house will be a gable roof.

    You don't necessarily have to have a ridge vent, but a vented attic does need an outtake vent of some sort. You can use roof vents, gable vents or a ridge vent; the main idea is to have your intake down low near the eaves (soffit vents) and the outtake up high, near the peak of the roof.

  91. Hi, I have a small cabin in northern michigan. We receive significant snow in the winter and we have an ice damming problem. We do not have soffit vents and I have had two contractors over and both have said there is not enough room to install the vents. Do you have any ideas as to how I can diminish the damming of ice? We have two large gable vents and a ridge vent. It is a ver small place, 700 sq. feet. Thank you, Brian

    A radiant barrier will usually REDUCE the possibility of ice damming. Ice damming is caused when the top of the roof warms above the freezing point the the lower part of the roof is below freezing. To prevent ice damming, you want a COLD roof. The roof gets warm due to warm air leakage into the attic AND from the home emitting radiant heat.

    Your priority should be sealing the attic floor first - the leaking air is not only contributing to the ice problem, but it is also a big energy waster. After you do this, then you're going to benefit from adding a radiant barrier. The radiant barrier helps keep the radiant heat from emitting from the home from hitting the roof. The result is a COLDER roof deck, which will reduce ice damming. Many customers have seen a significant reduction in ice damming after installing AtticFoil® radiant barrier. I would also suggest checking to make sure you have good attic ventilation, since cold air entering the attic will also help keep the roof COLD.

    For more info - here is a case study from a home in New York that was having a problem with ice build up on the roof:

  92. Hi Ed, I recently installed a wood stove the wall behind it gets really hot was wondering if a reflective barrier installed under hard wood paneling would help or if I should use some type of stone. As stone is really expensive I am looking for a somewhat more cost effective route. THANK U

    You should just use regular aluminum foil, not AtticFoil because of the scrim and the proximity of the heat of the stove. Another option would be to build a little brick wall like you suggested.

  93. Hi Ed, I have a 1800 sq ft double wide with a shingle roof. I am about to install a metal roof over the shingles. I have checked pricing for radiant barriers of differnet brands and they range in cost from 600 to 1000 dollars. Do you think there is enough energy savings to justify the extra cost? I will have a 3/4" air gap between the shingles and the new metal roof.

    I'm not sure where you are checking pricing but you can get 2,000 sq ft of heavyweight foil for under $300, with shipping included. Check it out: DIY Radiant Barrier Foil from
    As far as the return on your investment, you should read this article I wrote on Expected Savings by Adding a Radiant Barrier:

  94. Hi there, I live in the Austin Texas area which gets plain ugly during the summer. My plans are to build a stand alone shed/workshop 12’ x 12’, 16” centers. It is my intention to air condition the unit with a 6,000 BTU window unit. The roof joists will be exposed on the inside, hence no ceiling. I plan to use a radiant barrier on the roof plywood sheathing. The walls will be wrapped with Tyvec and the exterior will be covered with HardiPlank. From the inside I plan to insulate the walls with radiant barrier panels (between studs)and then standard R-30 fiberglass. Finally the inside walls will be covered with either dry wall or plywood, haven’t decided. My question is: Can radiant barrier panels and fiberglass insulation be used together as I have mentioned above? Thanks, Carmine

    This can only be done IF THE RADANT BARRIER HAS AN AIR SPACE ON ONE SIDE (preferably the back side between the exterior and the foil). To do this correctly, I suggest you follow the install instructions on this page: How to Install Radiant Barrier in your Walls to Keep the Heat Out.

  95. Forgive me if the answer is here to be found already, I am in a rush to re-roof my house in blistering hot south florida, my strategies are to put an ordinary shingle roof on it, then put $2400 EDPM acrylic mastic bright white waterproofer over it to reflect the sun, then either spray or staply a radiant barrier foil/insulation under the plywood from inside the attic. Question, is there anything extra I should be doing topside first? And what the best radiant barrier for hot humid climate?

    Honestly, if you add a radiant barrier in your attic across your rafters, it doesn't matter what kind of roof you have. At least, not really. Metal, tile, shingles - all those types of roofs will be subject to the radiant barrier blocking 97% of the radiant heat from outside from coming in via the attic. I'd strongly consider this before paying several thousand dollars on a roof. Don't get me wrong - cool roofs are awesome! But if you're looking for an economical solution, they aren't always the best route.  Another option would be to add the radiant barrier foil on the roof deck, under a roof that has a built in air gap.
    Go with a normal, double sided perforated foil on the underside of your roof rafters and you will be fine. Complete installation instructions here: How to Staple Radiant Barrier Foil To Your Attic Rafters.

  96. We had a new roof installed in June 2012. Everything seemed okay through the summer. Of course we did not get into the attic until Christmas time. When we went up there this past weekend to get boxes out there was alot of condensation in the attic and the boards were wet and some dripping was occuring. Now the boards are starting to crack and split. We think that this was defective roof and probably been leaking every since it was installed. Could this be possible? We have not had any large amount of rain or snow. Did have snow when we discovered the problem and again just two days ago. Please help so I know what to do when I have the roofing company out. THANK U

    It could be a leak ,or if you are in very cold climate something could have changed with the attic ventilation that is causing the moisture to condense in the attic.

  97. I have seen thick foam boards with an RB attached to both sides that are attached to the rafters in the attic crawl space. This is done in lieu of creating the "envelope" in the floor joists and knee walls. The whole idea seems to be to keep the attic crawl space near the inside temperature of the house. Have you ever heard of this, and do you think it is a good idea?

    This sounds like a version of a "foam encapsulated" attic. I did this on my new home:
    I highly recommend it for new construction, but it can be a challenge with some unintended consequences when done on an existing home.

  98. Our builder installed a radiant barrier for the attic before installing the roof shingles. When they were putting the shingles many nails went through the radiant barrier. Although it is not torned but it is punctured. Will that affect functioning?

    I'm going to assume the radiant barrier was put on BEFORE the plywood roof deck, meaning you can see the radiant barrier from inside the attic - in between the rafters. This really is the only way that a radiant barrier would work in this situation with no air gap. So, assuming that is the case, the nails pricking through the underside of the roof deck into the attic are not going to affect the foil's ability to block heat transfer.

  99. Could the radiant barrier be used for wrapping a water heater (in the crawl space) or is insulation still the best method? Any recommendations would be appreciated. Thanks

    You can use it, but you still would want a layer of insulation between the foil and the heater. They make pre-made water heater wraps (also called blankets or jackets) and they are usually less than $30 at home improvement stores or online.

  100. When installing a rigid vent on a new roof should there be a gap of about 5 or 6 ft in the center. All the homes I hve seen in my neighborhood have them all the way across the roof, except for a small area on each end.

    Normally a ridge vent is run on the majority of all "upper ridges." Having a small section without it is probably not a big deal.

  101. Hey Ed! Is this site still functioning? I'm installing radiant tubes in my house and I have a basement that is currently unheated but sits below all the rooms being heated. My question is it is absolutely necessary to have a radiant barrier for the tubes? I'm using Roxul R23 insulation because it will also help with sound transmission from people walking around upstairs. The radiant barrier is a huge pain and I have about 1000 sqft left. Can I just get by with the R23 between the joists in the basement ceiling?

    Can you? Sure! Just keep in mind that traditional insulation slows heat transfer, it doesn't stop it like radiant barrier. So while you can just use the traditional insulation, you would get the best results from a radiant barrier. It's actually pretty simple to install under radiant heat flooring - have you seen my article about installing a radiant barrier under radiant tubing?

  102. Hi Ed I Have a small 50 year old mobile home with thin walls. It has wood paneling and was thinking of stapling a radiant barrier onto the panel and then covering with strips of beader board. Just to help prevent heat loss. I don't have a way of doing foamboard and new paneling as the home is to small and would bring the walls in to much. Would this be a workable solution?

    No, in order for a radiant barrier to work, there MUST be an airspace on one side of the foil. If you sandwich the foil between paneling and board, the foil will act as a conductor, NOT a radiant barrier. If there is no air gap, then a radiant barrier is useless because with no air gap there is no radiant heat.

  103. Hi Ed. I live in Texas and had the foil radiant barrier put in a few years ago. I also recently had some soffit vents & 20 inches of insulation blown in. What's your opinion on adding a couple of solar ventilation fans? Thanks for your help!

    I'm not a big fan of solar fans since they are expensive and quit working as soon as the sun goes down. I'd rather have two wind turbines that will pull MORE air and work 24/7.

  104. I'm looking to test this minimum air gap with foil that's posted here and other places. I've already installed foil barriers in buildings where I've followed the guidelines, so I can see the practical value there. The reason that I'm questioning now is because I'm fitting out a motor-home, where space is clearly more precious. Surface emission/absorption interference effects don't usually start kicking in until the order of magnitude of the wavelength of the radiation is approached - and even with the longest IR we are still talking a maximum of 0.7 mm, and typically less than one tenth of that. So is this 12 mm+ gap effectiveness something that someone has measured (citations?) or is it just a shibolith that is handed around in the building trade, as being about the smallest reliable gap before "approximately touching" occurs over a significant part of a less than taught reflector in a gap with a tolerance approaching what its actual dimension is? So if i'm installing the foil in tension, on ribs an approx. 400 mm 16" grid distance, between glass-fibre bodywork and PIR foam (with its own foil, of dubious effectiveness), in a sealed air space (no insects or dust or moisture) and a minimum 10 mm (0.4 inch) gap - based on the job's practical limitations - what's the chances of exactly the same performance as with a half inch or two inch gap?

    I'd love to hear more about your results - I'm actually considering doing some testing in the next year on the minimum air gap theory as well. My initial thought is that there won't be a difference in performance between the two spaces - but I'd be curious to know what the outcome is. Please keep in touch!

  105. Mr. Fritz, I recently built a garage kit with sheet metal walls and steel purlins, and I would like to insulate the walls with radiant barrier. I plan to use 1 x 2 furring strips to create an air gap and then attach the foil to the wood. If I plan to use a space heater or a portable air conditioner in the garage, does the air space between the sheet metal walls and the foil have to be air tight to prevent condensation? Thank you in advance for your response.

    You will have better results with heating than with air conditioning using radiant barrier only. You would vent the space between the foil and the metal and try to make the space inside the foil envelope airtight. Really, you should add some interior insulation (see this page for an example: if you want to really condition the space. If you are just trying to temper and make a little more comfortable, than you will probably be ok.

  106. I currently have a garage that has no ceiling. Would radiant insulation work without a ceiling and no insulation?

    Yes, just staple the radiant barrier to the bottom of the rafters that frame the roof above the garage.

  107. Hi Ed, After some termite damage, I re-studded and re-sheathed 3 exterior walls of my house. Before re-siding, I am using the opportunity to wrap the sheathing with Attic Foil. The Zip Wall sheathing goes all the way up to the roof line, no soffits on these areas. I am installing the foil to keep heat out, so the I plan for the air gap to be just under the siding. There are 2 walls that have gutters to be installed.. I plan to first wrap all three walls with AtticFoil, I would next add fascia boards to rafter ends on two walls. Next adding furring strips (horizontally for vertical siding) to the foiled area (starting just below fascia boards) for air gap. I am assuming that the foil would not go under the fascia since it is flush with rafters The problem is that when adding siding, it will be 1/2" inch further out further from the sheathing than the fascia, causing an unwanted water edge just under the fascia. The installed gutter would cover some of this, but I am wondering if there is another way to install furring strips with the fascia and still leave an air gap but no rain edge. Maybe not complicated; but I am a little confused about best install method: 1. such as furring strips under fascia so both siding and fascia would lay flush together over the air gap- 2. or trim under the gutter to cover uneven break between fascia and siding.) Thanks in advance for your expertise. Chris

    Chris, you probably need to contact the manufacturer of your siding in order to determine the best way to install it with the furring strips. As far as the foil - it just needs an air space on one side - so wherever you get the air gap, face the foil toward it. It's simple, just get 1/2" or more of open air space for the foil to work.

  108. Is it true that space suits use a similar material and that it keeps heat inside the suit?

    Yes, radiant barrier technology has been used in space applications for a very long time.

  109. Hello: Thanks for your great web site! I have a lot of moisture in my attic and it has an ac unit resting above the rafters with insulation around it. When it runs in the spring and summer it seems like the moisture level increases upstairs in the bedrooms under the ac unit. You can almost feel the dampness in the bedroom. This is an older style 60s split level and it does seem to have some soffit vents on 3 sides but it looks like extra insulation was added before I bought the house and thus I'm thinking some of the vents are plugged.(there is an addition on one side and so there are only soffit vents on 3 sides). I have only a few sq metal vent caps on top of the 500 sq ft bedroom roofed area. I did notice that the vent for the bathroom fan is opened into the attic and is NOT vented properly so I'm having that vented properly to the side of the house. In addition it gets so hot in the summer upstairs in the bedroom with a musty smell that the bedrooms never really cool down adequately. I've shined a flashlight up into this small attic space and I see no evidence of mildew or mold. I am having heating specialist giving me a bid on an attic fan but I"m wondering if that is a good idea with the moisture problem and the air conditioner in the attic. Your advice would be greatly appreciated. Ted in Iowa THANK YOU!!

    I would never add an attic fan they usually cause more problems than they fix, see this article on Attic Ventilation Basics.  As for the musty smell, you could have a small leak in the condensation line that could make it wet but maybe not noticeable from below. You could also have some duct leakage which is causing the home to go into negative pressure and drawing in moist air from outside. If the second floor is hot, the first think you want to do is add a radiant barrier. Click here for info on how to install a radiant barrier in your attic.

  110. I recently built a new home in Florida. I used the same type of building technique of encapsulating the entire attic space which houses the AC duct work. Recently I discovered water droplet forming on the insulation in the attic space. The house had no vents. I just added roof vents as well as soffit. Do I also need to vent the front vaulted ceiling?

    If you had a fully encapsulate attic and then cut holes in it then you no longer have a fully encapsulated attic. Cutting holes in an encapsulated attic is just like opening windows. It's she LAST thing you would do. You probably have a moisture problem due to improperly sized/designed air conditioning system. I would look to have a HERS rater come out and evaluate the home.

  111. Hi Ed, Thanks for all the info. I have a 2,400 sq house in R.I. Built in 1982. I will be selling within a couple of years. I am having house painted and gutters replaced (old, hung too low). The roof is 2-layers, shingled and tight. I have Gable vents, but no soffit vents. While gutters are down and before house is painted, would it make sense to add soffit vents, even though I don't have ridge venting? (Would Gable Vents exhaust the air well enough?). Thanks for your help!

    YES! There is no rule that says soffits only go well with a ridge vent. I know of plenty of home that employ a combination of just soffits and gable vents. You need that air intake down low at the soffit level. That air moving through is going to be the main factor in lowering air temperature in the attic and keeping the attic dry. Definitely add the soffit vents.

  112. Hi Ed. I have an air gap between the roof decking and spray foam of .75 inches and have two questions. 1) what is the minimum air gap required for radiant barrier to work well, and (2) Will Spray Foam stick to radiant barrier, or will it slide off like butter in a hot pan?

    1. Right now (pending some more testing in the future to get an EXACT number) I wouldn't go with anything less than a half an inch on the air gap.
    2. The spray foam will not adhere (and if by chance it did, it wouldn't do it well) to the radiant barrier. The most common way people combat this is by adding a layer of foam board in the rafter bay BEFORE spraying foam. The foam adheres well to the foam board.

  113. My power fan in the attic keeps starting on and run about 20 to 30 minutes then stop for a while starts again even under weather temperature of 45 F. Is it normal? If not how to adjust it? Thanks.

    Have you checked the thermostat on the fan? This is the first place I could look. If that doesn't help, then it could be an electrical problem. One option you have would be to go for a passive system and just unplug the fan. The air will still find its way out.

  114. We have a 12x17 add on dining room. There are 2x12 floor joices with 8 inch cleaarance. The room sits on a footer. There isn't insulation under the floor and no vents under the floor. The foundation is dirt, there is moisture under the entire area. What is the best way to insulate. Do we need a moisture barrier on the dirt. do we need vents???? Someone mentioned fiberglass insulation with foil backing attached to the 2x12. Appreciate your advice. Ray

    Yes, it sounds like you don't have a vapor (moisture) barrier below. If this is true, then you can add fiberglass between the floor joists and then attach a SOLID/VAPOR BARRIER radiant barrier foil to stop moisture and heat loss from the home into the ground below. Here is an article on adding radiant barrier to a crawlspace that includes photos too.

  115. I am building a open porch cover and plan to in close is later. So the ceiling beams are exposed now and I don't want to see the foil will it damage it If I paint it or can I place the foil side up

    If you are just stapling the foil to the bottom of the exposed beams, then there will be an airspace between the foil and the decking, so you can paint the foil or cover it up because the topside (facing the sky) will be open to the air space so it will still work. Only one side of the double-sided foil has to face an air space.

  116. we would like to re-roof our sm.(864sf under air)cottage here in South Florida. a simple 4/12 pitch,no valley's etc(photo's attached). we will do the work ourselves(retired Homebuilder). vaulted/cathedral exposed beams,tongue/groove ceiling. no insulation. difficult to cool(5 ton ac)in July/August. have to keep shade tree's cleared overhead because of hurricane threat(1 1/2 blocks from ocean). definitely do not want to cover/remove ceiling to insulate. roof should be able to support weight of concrete/clay tile with radiant barrier. that would be one option,but not sure about aesthetics(curb appeal). maybe a low profile tile would look ok. would something like this work:remove worn asphalt shingles down to roof deck. add 1X4's vertically over radiant barrier to allow air flow from eave to ridge. lay 3/4" osb/plywood on top of battens. felt,metal roof panels/shingles on top of that. anything like this been done? thanking you in advance. Bob


    Yes, this can (and has been) done with great success. In fact, it's one of the few ways you can incorporate a radiant barrier with a traditional shingle roof. You can lay the PERFORATED radiant barrier foil over the old deck and then fur it out before adding the second deck. Then build the rest of the roof as normal for shingled roofs. This page might be helpful to you - though it talks about metal and tile roofs, but the principle of using the batten system is the same: How to Install Radiant Barrier on your Roof.