I still get this question all the time. “Can you explain why an air space is needed for a radiant barrier to work?” Watch this video for a complete explanation.
Basically it works this way. Radiant heat is heat that is transferred across either an air space or a vacuum. This is how the heat from the sun reaches the earth. Radiant heat acts similar to a sound wave. By definition, you MUST have either an air space or a void for radiant heat to even exist.
If you don’t have an air space then you basically have a solid. Heat can essentially only move through a solid by conduction. This is by direct contact. This is how an egg cooks on a hot skillet.
So, without an air space, you cannot have radiant heat. Without radiant heat there is no way to have a “Radiant Barrier”. In fact, because of the conductive nature of pure aluminum, if you install radiant barrier foil WITHOUT the required air space it will actually work AGAINST you and INCREASE Heat flow.
The bottom line is you MUST have an air space on one side of a radiant barrier for it to work.
Looking for more videos on this topic? Check out my posts below.
Ed
I live in California. I am accepting bids from roofing contractors to replace my old cedar shake roof with a stone coated metal roof system on battens. The existing roof has solid plywood sheathing. I’ve been studying radiant barriers and your explanation was excellent. I have several contractors that want to use a radiant barrier system you described with a 1/4″ insulation pad sandwiched between two sheets of aluminum foil.
A couple of the contractors want to put the radiant barrier UNDERNEATH the underlayment on top of the plywood with NO air gap. Doesn’t work as a radiant barrier, right? Also,virtually no insulating properties, right? Is there any value to doing it this way. Can your product go over the underlayment with a 3/4 inch air gap above the the bottom of the metal roofing?
Thanks So much.
Where can I purchase your product?
Gerald Freeman
Gerald,
You have two questions: 1) Does insulation (1/4″ foil/foam) under a metal roof do any good? and 2) Does foil without an airspace on one side have any value?
Answers –
1) Putting insulation at the roof line will ONLY help if the roof is a cathedral type ceiling. If there is ventilated air (an attic) below the insulation then it looses virtually all it’s value. Just like your front door. It has insulating value until it’s swung wide open. Putting insulation at the roof line for a vented attic helps some with heat transfer, but you really only need a radiant barrier to the outside (under the metal roof on top of the decking) and put the additional insulation in the attic on the attic floor.
2) You are correct. You MUST have an air space on one side of the foil for a radiant barrier to exist. By DEFINITION radiant heat is heat transfer WITHOUT contact – or in a waveform ACROSS a void. If you “sandwich” foil between two other products, then all three products become ONE solid with different conductive qualities. (heat can only move through a solid by conduction) In fact, aluminum is the MOST conductive of the three. So, in reality, putting aluminum foil (radiant barrier) in the assembly would actually cause MORE heat flow then without. It would actually work against what you are trying to achieve.
Yes, you can put radiant barrier foil under metal roofs. Here is the page for this with a video and pictures: http://www.atticfoil.com/radiant-barrier-shingles.htm
You can order online or via phone: AtticFoil.com
So, the current technology in Texas appears to be plywood/osb decking with one-side radiant barrier nailed to the roof joists, foil-side down. Then (possibly) roof felt directly onto the osb decking and then shingles or metal roof over that (directly screwed into the decking).
In this case, the only “void” or space is the attic, underneath the radiant barrier sheet glued to the osb 4X8’s.
Am I right that this means no radiant barrier? In other words, does the void/space have to be on top of the radiant barrier, i.e. foil?
Based on your explanation of the physics, I would assume so because once the radiation/waves enter the attic below the shingle/felt/osb/foil sandwich, the chances of reflecting back the radiation are gone, no?
And if this is correct, there are a large number of roofs being installed in Texas advertised as “radiant barrier” that are not barriers at all.
Thoughts?
Paul,
Foil backed decking materials have the airspace facing the attic – so, yes they do work and have the required airspace. These product like TechShield and PolarPly actually work off the EMISSIVITY quality of the foil in the Summer to reduce heat gain. When the foil is on the “cool” side it keeps the decking from “emitting” as much heat – it is technically NOT reflecting the heat back in the Summer. In the Winter, it WOULD be technically a “Radiant Barrier” since the foil faces the “hot” side or heat coming from the home.
Either way, foil backed decking is a good option if you have the opportunity to replace the deck. It’s not quiet as effective as stapling AtticFoil to the bottom of the roof rafters, but since there is no additional labor it’s a good “bang for the buck”.
I am about to construct a new home with Insulated Concrete Forms and foam sealed attic. The house is to have composition shingles. Am I correct that to get the air space I would need to put a layer of decking with a radiant barrier (with the foil side up), laths and another layer of decking, or is there another way? What would be your recommendation?
This would work great – in fact I did a similar system to this on my own house. You can achieve this with TechShield, or with AtticFoil attached onto plywood. You can do it like this: foil faced plywood facing up, wooden furring strips, foil faced plywood with foil facing down (toward wood strips) then felt and then shingles. Send me some photos of the install if you can!
Ed,
Is it really worth it, putting a radiant barrier under a metal roof with an air gap? If I understand correctly, a metal roof already reflects a good portion of the sun’s radiation away from the home by itself. Would there be an added benefit to having a fully-functioning radiant barrier underneath or would it just be redundant?
I’m looking at putting a new metal roof over my old shingle roof and was wondering if adding a radiant barrier with an air gap would help my house (and my AC unit) withstand the hot Texas sun. Thanks for all the info.
Armando
Armondo,
Thanks for the comment. You are assuming that ALL metal roofs are highly reflective. There are some, but most are not. Just because something is reflective does not necessarily mean it does not get hot and radiant heat downwards. Think about a chrome bumper on a car. It is VERY reflective, but you would not want to sit on it on a hot and sunny day.
Putting a radiant barrier below ANY type of raised roof is the best thing you can do both from an energy perspective AND an economic perspective. There is nothing that can make a bigger impact as far as heat gain for less money. Radiant barrier under metal and tile roofs is the fastest growing part of our business. Both customers and roofers are realizing what a great opportunity it is to make a big impact.
Call us at 800-595-8772 if you have any other questions. AtticFoil.com
Hi Ed,
I am renovating an RV that I will have to live in as I travel throughout some very hot states and its like an oven. I can feel the paneling on the roof and and walls and its quite hot. Its construction is metal on top facing the elements, then 1 1/2 foam board,.then 1/4 paneling all this is glued together.forming on panel. I put some foil roll (aluminum on both sides with a foam core that is 5 mm thick) and I stapled it directly to.the paneling. However it was still quite hot to.the touch. Is this because I lack an air gap? I had kind of..thought this method would be similar to an attic with the foil barrier installed under the roof decking so.the..foil faces the attic. In that scenario, would the attic be the air.gap? And does this not.work in the Motorhome because I’m in the “air gap” which is I guess my living space?
Also I did not cover the foil barrier nor do I plan to for right now. Will that.affect my radiant benefit if I remove the foil and re-install it over a 1/2 air gap of plywood furring strips?
Harrison,
If the foil is adhered to a layer and open on the RV side, it SHOULD be hot to the touch because the moment you touch it, you have eliminated the air gap and the heat will flow via conduction right into your hand. This is why the air gap is critical. A better way to test it would be to hover your hand right BELOW the foil and you should not feel the heat radiating like you would if the foil was not there. Truthfully it’s probably best if the foil is closest to the outermost layer, but it will still work to prevent heat from emitting into the space below the foil. Keep in mind that the total assembly will probably be a little warmer since it does not have the ability to vent some of the heat and since you have traditional insulation in the roof already and it hold heat well. In this case, you’re just aiming to get the best results you can with what you have to work with. That far down into the RV, I don’t know that adding the furring strips is going to give you any different of a result. It will just change the way in which the foil blocks the heat, but the outcome (97% rejection) is the same.
doing addition. radiant barrier osb already installed on new const. my existing house which is about 3,000 sq. feet has slats that were filled in with more wood slats when the comp roof was done 30 years ago. my dilema is, do i remove all those slats and sheath in 5/8 radiant barrier or just put regular osb over existing slats and save about 3,000? i am putting an exhaust fan and going to blow in new insulation in the joist areas after the project is done. My other question is that I am having a vaulted ceiling in my new den. it is a big room, about 19×30 and the walls start at 11′ and it vaults to about 14′ it has 2×10 rafters and sheathed in radiant barrier osb. When insulation is put in the rafter bays is it ok if it makes contact with the underside of the radiant roof sheathing or do i need to have a air gap? thanks
Nick,
First, $3000 additional for radiant barrier decking is crazy. The actual cost for radiant barrier decking is only about $2-3 per sheet more. You will need about 100 sheets for a 3000 sq. ft roof which is $200-300 in cost. There is NO additional labor to put in on. Even with a mark up I think you should get it for less than $700 additional compared to regular decking. There is labor cost to remove the slats, but it still seems high. A more cost effective method would be to spend a few hundred dollars on AtticFoil Radiant Barrier Foil and staple to the bottom of the rafters inside the attic. You will actually achieve better results than the foil decking. As for the vaulted ceiling, yes you MUST have an air space between the insulation and the foil. Without it, you will be conducting the heat directly from the deck into the insulation.
Thanks for the response. Well I guess the cost of the increased thickness in plywood and going from 7/16 over existing slats to 5/8 radiant barrier plywood is one of the increases. The cost of ripping off all the slats is about 800 bucks. So maybe it isnt 3000 but is the payoff for doing this worth it? How long until the payoff in utility costs for stripping down and doing it in the radiant plywood? I’m in so. california, summer more extreme than winters here. I decided against my wifes wishes to go with the grand sequoia weathered wood comp shingles instead of the black color for obvious reasons also. As far as the vaulted ceiling, im more confused than ever. Had a guy out and all they do is spray in foam. The stuff looks impressive like the walls of an ice chest. He says this is the way to go with four and a half inches against the bottom of my roof deck. I asked him about it contacting my radiant barrier plywood and he says they do it all the time and this method is being more recognised and accepted. it will be air tight and no condensation problems and it seals all the nooks. I would be a little nervous about it in contact with the foil back. This is a no-no to have any contact with it, which i know you know about. I still would have to run it by my inspector to have a non-ventilated ceiling. The cost is 2,400 just for this 28×19 room to do in foam. I called my guy who bid on doing my whole addition in conventional fiberglass for $1,700 and he says its a waste and i wont recoup the money. He suggested putting a high-density r-30 and venting the ridge instead of having a sealed envelope. The 4.5 inches of spray in is equal to r-30 so maybe its not worth the money, and the venting and roof ridge vent wouldnt be very costly. Unless he wants to spray 7″ and give me an r-45 value for the same money, maybe I should pass on this. What do you think? What would you do? I really appreciate your input. It is hard to get an unbiased opinion.
Full foam encapsulation is the best way to go over the long haul. Increase energy efficiency, plus you can usually downsize the AC equipment and offset some of the expense there. It will not hurt to spray foam on the bottom of foil, you will just loose the radiant barrier benefit.
Ed, thanks so much. I’m having the roof installed right now, and am doing conventional non-vented ridge on vaulted area. Went to the city and they dont have a problem with sealing and not venting and using spray foam. Now I will try to get the price down a little or have them spray a little thicker. thanks again
ed,
i’m residing my house…replacing the old t-111, sheathing, and fiberglass roll insulation. given what i’ve read it would make sense that one could see a benefit of using foil-backed if installed as sheathing on the sides of a building as well, assuming it was installed foil-side facing the studs. if i’m correct, why don’t i see it mentioned anywhere online?
thank you in advance for sharing your insight with us diy-ers.
Nero,
I don’t quite really understand what you mean by “assuming it was installed foil-side facing the studs” Take a look at this page regarding radiant barrier putting behind vinyl and hardi board type sidings?
i was referring to a foil backed OSB like (https://www.gp.com/build/product.aspx?pid=5857)
as exterior sheathing, installed with the foil side inward towards the air gap created by the studded interior wall.
my apologies, sometimes i mess up the lingo.
until again, nero
Nero,
If you’re putting the foil facing inside, toward the inside of the home, then you run the risk of eliminating the necessary air gap when you fill the cavity with insulation. Insulation doesn’t count as an air gap. To do this application properly you would need to ensure the foil doesn’t come in contact with anything for at least 3/4″. Photos and tips are on this page: How to Install Radiant Barrier Foil Inside Walls.
ED,
I HAVE A VAULTED ROOM INCLOUSER 4X6 RAFTERS WITH 1 7/8″ T&G SUBSTRIGHT, AND A COMP ROOF COLOR BLACK WHATS THE BEST WAY TO DEAL WITH THE TEMP AT THIS POINT, FROM THE INSIDE ,RADIANT BARRIER ,FOAM OR BAT STYLE INSULATION.
THANKS
GARY
Gary,
Here is everything you need to know about Installing Radiant Barrier In A Cathedral Ceiling to keep the heat out. Video and instructions. Let me know if you need more info.
Hi , I have 4 quotes for roofs for a small detached one story 350 Sq feet apartment. Live in Cal- mild summer and winter, summer can get hot 10 days 98 degrees remainder in 80’s . I no nothing about the materials . is it necessary to apply OSB or radiant barrier solid sheeting over existing roof deck of 1 by 8 boards, and if OSB will 30 lb roof paper help with insulation. or would you recommend going for the foil or solid radiant sheeting. We are trying to stay in budget and did not know what would be recomended. They are going to put in heating and eyebrow vents too.?
Your best (most economical) option would be to use radiant barrier decking in the construction of the roof. This will be installed so the foil side is DOWN, facing the attic space. Then, you can build a normal roof above that. Felt paper is more for waterproofing and offers no real insulation value. If you go with the radiant barrier decking, then add your regular insulation on the attic floor, as much as you can get in there. If the apartment will not have an attic space, then you should use the Cathedral Ceiling Method to install the radiant barrier AtticFoil.
I am having my home re-roofed (from wood shake to compostion tiles) and they put the radiant barrier face down on top on the rafters and remaining board – facing the attic. Is this adequate or should they have put some kind of spacers between the radiant board and the existing board/rafters??
This is an OK method considering you are switching from wood shake to composition. You will loose the benefit where it is “sandwiched” between the existing cross lathing and the new roof deck. If no laths are removed, then you will get about 50% benefit since about half the space would still be open. I would recommend removing every other lath and then putting the foil down before the new deck. This will help with the structural strength and allow for more open space to provide a greater benefit.
Thank you Ed..I have talked with the roofing company and explained my concerns. I’m waiting to hear from the district manager. Unfortunately, I’m a lay person and I don’t know how serious they will take me. I’ve not only read your articles but read several others supporting the importance of the airspace underneath.
We live in Texas — Our garage is a two car type with a metal door .
I intend to install 3/4 ” foam rigid panels that are aluminum foil on one side.
Should there be at least a 3/4 air gap between the panel and the garage door . Which side of the panel should the aluminum foil be facing ? The metal door or facing the inside of the garage ?
Is there a better alternative to improve the insulation
thanks Richie
Yes, the foil should have at least 3/4″ of an air gap, so if you put the foil facing the door itself, you’ll want to install the panels so they pop out a little and don’t make direct contact between the foil and the door. Complete install instructions and a video here: How to Install Radiant Barrier on a Garage Door
Using the foil-faced foam board in the way the install page shows is a great way to insulate the door. For further improvement, consider covering the walls & the attic space above the garage with radiant barrier as well.
Ed,
I have been looking at your product for a while now. I’m building my home and I’m trying to make an energy efficient home.
I have been doing a lot of research and I am hearing mixed ways on how to properly installed a radiant barrier with a metal roof. Some people are saying that there should be an air gap in order for a radiant barrier to be affective. So if that is true that makes me think the OSB with the radiant barrier wouldn’t be an effective solution since the metal roofing would be right on top of the OSB.
Here are the options that I have in mind.
1 – Metal Roofing with 7/16″ Radiant barrier OSB decking with the foil side down then attic foil stapled to the bottom of the roof rafters.
2 – Metal Roofing with regular 7/16″ OSB decking then attic foil stapled to the bottom side of the rafters.
3 – Metal Roofing with 7/16″ Radiant barrier OSB decking and no attic foil on the rafters.
I would like to know which one is the best option in your professional opinion.
Thanks
If you are doing a metal or tile roof, then you should try to get the radiant barrier on TOP of the deck directly under the airspace created by the metal or tile. Putting RoofingFoil under metal and tile is the fastest growing insulation method for these type of “raised” roofs. Take a look at our new website http://www.RoofingFoil.com for information on how to install a cool roof radiant barrier in metal and tile roofing systems. Sorry for the late reply. Your comment went to the junk folder.
Ed,
In an older 1.5 story house would there be any benefit to install a radiant barrier in the upper room? If the sloped ceiling(roof deck) had already been insulated with closed cell spray foam? Even if an air gap was present between the insulation and drywall? Or would this create an even hotter roof?
Keith, I don’t really see any big benefit to putting AtticFoil “inside” of the insulation. It’s kinda like putting foil INSIDE a refrigerator as apposed to wrapping it. In general you always want to make radiant barrier your 1st line of defense against radiant heat and “regular” insulation – foam included to be your 2nd line of defense against conductive heat. It would help SOME, but I don’t think the small additional benefit is worth the time/money effort.
Hello Ed,
Thanks for the your articles. I have an older house In Austin and want to retrofit with both radiant barrier and spray foam to get a air tight seal. Obviously there are tons of conflicting articles on this. I think the way to do this is, under the sheathing go between my rafters with 1/2 inch ridged foam one side faced with radiant barrier. Radiant barrier faces up but there is a 1 inch air gap created with small 1×1 stand offs. Then I can spray foam directly under this as there would still be 4 inches of rafter space. I would block off about a foot or two before the eves and at the ridge allowing air to come in from the soffit and up and out through the ridge vent. I have read several articles that said if the radiant barrier faces up with the 1″ air gap the RADIANT heat wouldn’t be reflected but conducted through the ridged foam board and then through the foam insulation. To avoid the issue all together I thought about just using spray foam directly on the sheathing but read this voids your roof warranty as it doesn’t allow air flow under the sheathing overheating the roof assembly. One other option would be to put full 4×8 sheets of the ridged foam backed with Radiant barrier directly onto the bottom of the rafters leaving a couple of feet at the eves and ridge then just spray foaming the attic floor. A few different option here but what are your thoughts which would you do, or would you do something different? Thank you, Travis
You may want to consider doing this method: Radiant Barrier In A Cathedral Ceiling But, instead of adding batt insulation and sheetrock, just spray foam directly to the back of the foil and fully encapsulate the rafters by at least a couple inches. This will provide a radiant barrier, ventilated channel, and minimize thermal bypass through the rafters. You will achieve the same as your first proposal, but the foil alone is a lot easier to work with than foam board.
Hello Ed,
Thank you for all the advice you and your site provides! Hopefully this question post as I tried last weekend and don’t think I was able to. I am located in Austin Texas and want to use Radiant Barrier and Spray foam. The ideal goal is to have an air seal as well as a radiant barrier at the roof line. Is the below assembly a good solution in your opinion
Here is my thought (please let me know if you agree, disagree or would tweak in some way). There seems to be may contradicting articles on the web about this but I have looked at the science and feel I have a decent grip on the best way to accomplish it. Step one, 1”x1”x5” standoffs nailed to the rafter against the bottom of the roof sheathing. Then attach ½ in ridge foam with radiant barrier cut to fit between the rafters to the standoffs creating a 1” air gap. The foil side of the 1/2” foam is pointed towards the sheathing/roof. The ridged foam stops short of the eves and goes down to meet the attic floor. This allows air to come in from the eves up through the air gap and out through the ridge vent. Next spray foam is applied to the underside of the ridged foam 4” thick or even with the bottom of the rafters. This would seal the entire attic (where my HVAC equipment is) and provide the needed radiant barrier for maximum benefit (I think). If this is done I would pump some/minimal conditioned air in this space as well.
Method 2 – Since some argue the foil will conduct heat and then transfer the heat through the spray foam into my attic, they prefer the ½” ridged foam to be installed on the bottom of the rafters with the foil facing towards the attic not roof. In addition, they prefer not to seal the attic and just stop the ridged foam board with Radiant barrier a foot short of the eves and roof, allowing maximum air flow. If this is the preferred method then I could spray foam the attic floor, only negative here is the HVAC equipment isn’t in a conditioned space. Maybe the Radiant barrier reduces the heat enough make this a non-issue. This seem to use less labor but maybe less effective.
If it wasn’t feasible for you to remove the roof and decking which of these methods would you prefer or would you use a different method? Thanks in advance for any feedback.
Travis, did you see my article on combining spray foam with a radiant barrier? In Austin, TX I would definitely go non-vented full foam attic. NO Questions! I’d like to talk to you on the phone to help further. One of the challenges of foam is air conditioning. I did my whole home in Mitsubishi Multi Port inverter units. The results are simply amazing with the foam. You need a system that will operate at part-load and provide good dehumidification. I can also offer some good advice from first hand experience and from many customers and contractors on how to combine radiant barrier with a foam enclosed attic.
i am building garage with upstairs room built into trusses. so there is tiny “attic” at top, then a cathedral like sloped section, then eaves. i am using radiant barrier osb as roof sheeting. question is regarding ventilation… i intend to use some kind of thin plastic baffle/standoff to prevent my mineral wool batts from contacting the foil underside. But moist air from inside building (there is a bathroom), could possible condense on the cold osb foil. But do I care? It won’t rot because the aluminum foil will prevent moisture contact with osb! Only other way I can think to protect osb is spray closed cell foam but this would eliminate needed air gap.
PS An old engineer friend of mine told me that if i applied tar paper over aluminum foil facing sky on roof the foil would still reflect a lot of heat because without some “thermal grease” or gooey interface between tar paper and foil there would be very little actual contact, like 90% no contact or more. but tiny air gaps. plausible? does IR still launch if air gap is tiny or is there some wavelength inhibition?
If foil worked under shingles, every large product manufacturer would make/sell it. There may be a “tiny” difference with/without foil but it’s not worth the extra cost. We have done testing and the temps are the same with or without foil products “sandwiched” between the shingles and the deck. Trust me, no one wishes it worked more than me. I’d sell a lot of foil.
Quick question. My contractor is installing the Radiant Barrier ply on the existing roof slats which has minimum gap between them. Also we are installing solar reflective shingles.
Is it advisable to install Radiant Barrier on top of the existing slats? Would the Radiant Barrier work or it will cook up the shingles?
It will not cook the shingles, but wherever the foil decking has contact with the wood slats you will loose the benefit of a radiant barrier. No space = No Radiant Barrier.
I’m in Southern California (climate zone 3) and doing a reroof. 75% of the ceiling is vaulted with no attic (2×6 or 2×8 rafters with drywall). Currently the rafters have R11 mineral wool and are vented with soffits to a ridge vent. Sheathing is 1″x6″ solid shiplap. It gets very hot upstairs in the summer (particularly in the south-facing room).
Since I am redoing the roof, I also want to improve the insulation. What is the best way to reduce heat gain in the summer?
I’m currently looking at the following (some or all, no particular order):
-Use cool roofing shingles to reflect most energy gain
-Create an unvented roof (seal the soffits and ridge vent) and add air membrane over sheathing
-Replace R11 mineral wool with R23/R30 based on rafter size (2×6 and 2×8)
-Add 2-3″ of polyiso foam over sheathing
I feel like the cool roofing shingles and air barrier will have the most impact. Is updating the mineral wool or the rigid foam overkill?
I’d look to using a Radiant Barrier Roofing Underlayment under a roofing system that has an air space. This is by far the best method when installing a new roof. My second choice would be to add polyiso board over the sheathing. Also, look at the different radiant barrier videos on the homepage.
Hi there, Most of my experience is in northern climates, running a handyman business in southern NH plus quite a few houses owned personally. However I’m now working with a production builder in Florida & having to learn about block walls & radiant barriers in a hurry. Paid a thousand dollars for a radiant barrier on the roof so thanks for explaining that the foil on the OSB deck boards is about $3-5 dollars more (2018) and yes, for 2200 sq ft home, it confirms that builder has a 200% markup. Of course I couldn’t avoid this but I will be ripping out & replacing kitchen, bathroom & 100% of the flooring after closing to get higher quality products at lower cost than they wanted to charge … because I know what most things cost!
So now I have a similar issue with insulation for block walls. County code says R4 if installed outside, R6 inside, Wednesday I finally saw in one other house, they’re installing FiFoil’s AA2 product which is only R4.1 and apparently getting away with this because they can meet compliance with performance? Guess I’ll not only be participating in their HERS inspection … and then paying for my own to make sure it was done right.
Talked to Fi-Foil yesterday and learned that their product which appeared to me to be nothing more than a band-aid to make up for a building goof (read my blog post,
https://hometipsforwomen.com/wall-insulation-kind-installation) … is nothing more than a radiant barrier, not insulation. It’s simply kraft paper on inside, foil facing open cavity with furring strips that are closer to 5/8ths than 3/4 inches.
So my questions:
1. How would you compare paper backed foil to foil faced, 1 inch foam board for block walls … Orlando area with 60% humidity?
2. My experiment will be to add my own radiant barrier plus insulation to garage walls (they did get attic radiant barrier) to test effectiveness of my solution versus builder “cheapest” solution. Comments and recommendations for this appreciated.
1. My opinion would be that in both products, it’s the aluminum layer that’s getting results and blocking heat. I go into more depth about these products on this page of my website: AtticFoil compared to Other Foil Products.
2. A garage doesn’t typically need insulation (unless you’re talking about the wall that attaches the garage to the living space). In a garage space (or really any non-conditioned space), there is nothing better to temper the heat gain that a radiant barrier. These structures will greatly benefit from the addition of foil on any and all sides that catch direct sunlight and since they are not conditioned, you don’t really need to have insulation (fiberglass, foam, etc.) in there. Ideally you’d get radiant barrier foil on all 4 walls AND the ceiling, to get the best results in the garage, but even just doing the ceiling (roofline) can make a big difference in how it feels in there.
First, thanks for the info. I’m amazed by how many crooks are selling finished products with no air gap.
Questions:
When doing the garage door, can you face the foil inward, toward the garage? Until reading your site, I’d read that it doesn’t matter which side the foil faces, and the room itself becomes the air gap. As for the garage attic, would venting increase the dust coating on the foil?
I have foil/polyiso sheets that are white with ugly advertising on one side that I was going to use in a barn. Is it bad to face the foil side toward the room? Does the white side have a function?
A lot of places have window shades for sale, dishonestly claiming radiant properties. Can you think of a way to make shades with attic foil and and create an air gap? Can the reflected heat hurt a window?I’ve seen honeycomb shades with foil in the voids, but they are very expensive.
Yes, you can face the foil inward toward the garage and as long as the foil remains uncovered then it will utilize the garage as the air gap required for it to work.
Venting shouldn’t cause problems with the foil collecting dust. The dust is very unlikely to be light enough to be carried upward by vented air but then all of a sudden heavy enough to fall and stay on the foil. It can’t be both.
White coatings on insulation usually just serve to look nice. They don’t offer any reflective/heat barrier qualities. Ideally you want your foil closest to the metal with the air gap between the foil and the metal, but if not it can still work. Again, like the garage application, if you face the foil INWARD, you still have to have the air gap. So you won’t be able to cover it or put up drywall, etc. without first furring it out.
I’ve known of many of my customers making curtains or shades out of AtticFoil but I don’t have any details on exactly how they did it. You will lose all light by using foil versus a window tint/film. The best way would be to do it in a way that does not require constant rolling/unrolling of the foil because it wasn’t meant to be handled like that. In commercial applications I’ve know customers to just run a wood strip across the top of the wall/window area and then staple the foil to it so it hangs all the way down to the ground, just like a curtain.
Are any of the semi-transparent mylar window products effective?
Seems like an oxymoron…
Lyn,
There are a couple that do a decent job – better than nothing. None of them are going to perform like a radiant barrier that blocks 97% of the radiant heat.
Hi Ed-
I’ve got built up trusses in my attic and was about to install plywood floor over the trusses for additional storage space. Before laying the plywood I was considering a radiant barrier over the built up truss/insulation and then placing plywood directly on top. Now with explanation of air gap would I be better served to place the radiant barrier on the underside of the roof rafters. I had originally thought on top of the insulation and under the attic plywood flooring to reduce the heat on the underside of the roof shingles. I have an electric attic fan set to a thermostat to vent heat as well as continuous soffit and ridge vents.
Any advice you have would be greatly appreciated. Thanks!
Bill
Bill,
If you’re using the attic as storage space, you should staple the AtticFoil up to the bottom of the rafters. Learn more about why this method would be best in your situation: Staple Up or Over the Insulation? Which Method is Best for Installing Radiant Barrier?
Hello Ed,
I have a 10×14′ shed with radiant barrier OSB used on roof and all walls, foil side properly down/in. I want to insulate the shed so I can work comfortably in summer and winter. Any idea how to insulate without violating the 3/4″ air gap?
Thanks!
A baffle vent would be perfect – it will maintain the air gap between the foil and the baffle, and then you can add insulation in the cavity after that.
Hello Ed.
I have “Cool-Ply” underlayment over my rafters, under shingles, which sits on former cedar shingle lath work. It’s been in place over 20 years. The rafters and lath heat up due to transfer in the Texas sun. Would adding a second barrier under the rafters help much? Yesterday I measured heat on shingles to be 135F, barrier to be 94F and rafter/laths 120F. My attic routinely heats up to 110F+. Ridge vents run the length of the roof line.
Felix, Absolutely it will help! It really does not matter if you a traditional deck or an old cedar shingle roof with overlay. It gets HOT and will radiant the heat into the attic and into your insulation/home. Simply install like it’s a standard attic. Just Staple Up the AtticFoil to the bottom of the rafters.