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. If it doesn’t, just use the form at the bottom of the page to submit your question. I’ll get you an answer just as soon as I can.

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

Ed Fritz,
The Radiant Barrier Guru

Questions:

  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: http://www.atticfoil.com/radiantbarriercontractors.htm

    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

    Karen,

    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) atticfoil.com

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

    Ed

  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: http://www.atticfoil.com/best-install-method.htm

  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

    Frank,
    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: http://www.greenbuildingadvisor.com/community/forum/general-questions/16684/it-true-home-loses-10-heat-through-conduction-25-through-con

  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 AtticFoil.com 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: http://ratepoint.com/seereviews/38081

  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? http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table
    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: http://www.atticfoil.com/faq.htm

    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

    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: http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table
    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

    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: http://www.atticfoil.com/video-faq-how-much-cooler-after-radiant-barrier.htm

    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 www.AtticFoil.com 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: http://www.radiantbarrierguru.com/new-videohow-to-install-radiant-barrier-foil-into-a-cathedral-or-vaulted-ceiling/

    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

    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 AtticFoil.com - 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: http://www.youtube.com/watch?v=CjwZXoRzRiM&feature=player_embedded
    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: http://www.radiantbarrierguru.com/new-videohow-to-install-radiant-barrier-foil-into-a-cathedral-or-vaulted-ceiling/
    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: http://www.atticfoil.com/radiant-barrier-fire-test.htm
    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 questions.....is there a way to call you?

    You can call us at AtticFoil.com, 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: http://duro-last.com/


Ask a Question:


Question:
Email: 1

1 - Notification of when your question has been answered. (Optional)

Subscribe to RSS feed

Comments are closed.