Foil Under Shingles Will NOT Create A Radiant Barrier Unless There Is An Airspace On One Side Of The Foil.
At first it sounds reasonable. You are getting a new roof, so why not scrape off the shingles, put down roofing felt, THEN radiant barrier foil and THEN shingles right on top. What an easy way to install a radiant barrier, right? I also get asked if eShield, SolarGuard or Bubble Foil Insulation will work.
Unfortunately you just wasted time and money for virtually NO additional benefit.
Radiant Heat by DEFINITION is electromagnetic radiation that travels in a waveform ACROSS a void, either an air space (or gas) or a vacuum. Without this space you CANNOT have RADIANT HEAT. Therefore, if NO radiant heat exists you CANNOT have a radiant barrier.
If you have items “sandwiched” together, you will get conductive heat. It is usually impossible to have radiant heat through solids. (some exceptions are transparent solids like glass, water etc.)
I keep hearing of some roofers starting to push foil products installed between the shingles and the roof deck as radiant barriers.
If you are getting a new roof, beware of roofing companies who are selling radiant barriers under shingles. Radiant barriers without an air space don’t exist, they can’t exist, and they will never exist. They laws of physics always apply. Remember: No Air Space = No Radiant Heat = No Radiant Barrier.
Attention roofing companies: If you wrote on your invoice that you installed a “Radiant Barrier” in this method you should contact the homeowners, and make good on your mistakes.
Radiant Barrier Under Tiles with Required Air Space
What do you do if you are re-roofing and STILL want a radiant barrier? There is a way to incorporate radiant barrier foil into a re-roofing application. The ONLY way is if you can create an air space on one side of the foil. There are several types of roofs that have an air space between the roofing material and the roof deck. Barrel-type tiles, or roofs installed over wood battens, which create the needed air space.
With these types of roofing systems, a radiant barrier can be incorporated easily and economically. Simply roll out roofing felt or another type of underlayment. Then, roll out perforated radiant barrier foil, install battens as per manufacture instructions and attach roofing product. It is also recommended to “notch” the battens or leave spaces between the battens to allow for more airflow between the roof deck and the roofing material.
This method of installing a radiant barrier is low cost, and very effective in reducing heat gain into the home. Plus, it is profitable for the roofing contractor. Homeowners will appreciate saving money and having a radiant barrier installed the right way.
 Foil Installed Before Installing Standing Seam Metal Roof |
 Foil Installed Under Roof Using Battens To Create Air Space |
 Foil Installed Before Metal Shingles With Air Space |
I've written several other posts on this that you might be interested in. Check these posts below:
Tags: Attic Insulation, foil installation, foil insulation, radiant barrier, radiant barrier roofing underlayment, roofing felt, synthetic roofing underlayment
Thanks for your explaination on radiant barriers. Since you have identified that when things are sandwiched together they produce conductive heat, will a Thermal barrier be benificial to reflect away 97% of the conductive heat? In other words is there a beneift in putting a thermal barrier on the roof? I really need to know if having a thermal barrier that reflects heat away will help keep my attic cooler? If so, in your opinion how much? OR is it really a wast of money? A reply ASAP will help me since I am in the process of changing out my roof.
Thanks
Danny Williams
Danny, you can’t “reflect” conductive heat. You can only slow it down since it travels through a solid. This is the concept of R-Value. Since radiant heat is in a waveform, it can be reflected. The problem with putting any R-value on a roof is that the roof is normally not really part of the “thermal envelope”. The thermal envelope is usually your walls and ceiling. The roof just keeps it dry. So, you want R-value on your attic floor and radiant barrier at the roof. This is like putting a refrigerator in the shade.
So I’m confused. Radiant Barriers do work but only on the inside of the attic then?
Hi, totallu understand your concept. Question is can aluminum “shake” roof panels be applied over battens ?
I would think the extra air gap would assist in damaging the tiles if walked on. Same for most any metal panel.
Dante,
Aluminum Shake Panels? Like these?: Radiant Barrier Under Metal Roofs I think it all depends on the specific brand. You would need to check with the manufacturer.
Back in 1992 I was on a framing crew building a custom house. The architect specified 1/4″ X 4′ X 8′ panels that were waxed cardboard with one foil side and one white side. These were affixed to the roof deck over felt, then battens, then metal roof. I am soon going to put a metal roof on my house. Any idea what those panels are called or who distributes them? I would like to put something more substantial than “foil” under my battens, but I do not want to replace the OSB roof deck with the new foil sided OSB.
Thanks.
Thanks for you comment. I have never heard of the product you mention. My concern for a cardboard based product would be deterioration over time. I think bugs might think it is “food”. You said you want something more substantial than “foil”. AtticFoil radiant barrier is a foil laminated to a virtually tearproof inner woven scrim material. We have many roofing contractors using this product and have never had a single complaint about durability. Here is the link to the page for Installing Radiant Barrier Under Metal Roofs. You can also get a Free Radiant Barrier Sample too.
I’ve got a relatively new (7 years old) composition shingle roof. It’s in great shape, so we don’t want to replace it (we’re planning on moving in the next 5 years). HOWEVER, there is no insulation between the shingles and our ceiling!! It is literally shingles -> wood -> ceiling. Is there ANYTHING we can do? As I’m sure you can imagine, it gets hotter as the day wears on, the ceiling/roof literally bakes us
You definitely would benefit from a radiant barrier and some r-value up there. Take a look at this page: How to Install Radiant Barrier and Insulation in a Cathedral Ceiling for more information on how you can achieve this. Unfortunately it IS going to require removing the sheetrock to gain access to the roof cavity, but this is cheaper than tearing off the roof and doing it from the outside. The results are immediate and the comfort is drastically improved.
There is a better way then ripping off drywall. If I were you, I would check into having a company blow foam into your walls. They would drill a few holes in the walls and fill up the cavity with foam. Not cheap, but better than what Ed says. Good luck.
Craig
Craig,
Charles is talking about having a true cathedral ceiling. These are rafters with sheetrock on one side and the roof deck on the other. He or I never proposed ripping off the drywall. He asked if he should lift the roof deck while working on/replacing the roof. This is a great option if he has it. He can insulate the space between the rafters (from the top) while the deck is off. Then, lay the deck back down and proceed with the radiant barrier and stone coated metal roof over the batten system.
While I understand the idea of an interior mounted “radiant barrier” and the flow of heat to lower the attic temperature, why would a product like “POLARALUM” which is a “thermal barrier” not work as you claim? That foil underlayment at the shingles is used all over Texas and actually acts as a reflective .97 UV block to eliminate the heat buildup from sun rays. Much like a skin sun block. Factory Mutual has evaluated and certifies this product.
Robert,
I think you are confused in the difference between UV – Ultraviolet Radiation and IR – Infrared Radiation. If it was installed on top of the roof with the foil facing up then any product will stop UV and reflect IR. The problem is that when you “sandwich” the foil (any product including AtticFoil) between two products it becomes a “conductor”. Here is a video to explain the Difference Between Radiant Heat and Conductive Heat. By definition, radiant heat is transfer by NON-CONTACT from one object (hot object) to another object. If you don’t have radiant heat, then you cannot by definition have a radiant barrier. I wish more than anyone that foil between the shingles and the felt or decking helped. My sales would go way up! As for the Factory Mutual certification, if you really read the information, they have certified the product as a roof underlayment (which is is) not anything to do with rejecting heat when installed between shingles and the deck.
Changed my roof from cedar shake to composition shingle. Installed cdx plywood with a aluminum foil backing on the inside of the roof decking.Decking was attached to the 1×4 wood strips that run across the length of the roof. If that is a conductive barrier how do I correct the error ?
If foil is attached to the 1×4 strips it will create a air space between two aluminum sheets. What does that do ?
Jerry
Jerry,
If you put the foil directly on top of the old 1×4 lathing you will get a reduced benefit. Where the foil decking is “sandwiched” you will get no benefit as far as a radiant barrier. The “open” areas between the lathing, where you can see the foil from inside the attic (usually about 50% of area) will still help some. Because of thermal bypass into the lathing you are probably a little below 50% effectiveness. This is better than nothing. You can still come back and staple Radiant Barrier Foil to the bottom of the rafters and get great results. The first layer on the deck will act as a filter and let some of the radiant heat through. The layer stapled to the bottom of the rafters will reflect virtually all the radiant heat that makes it past the roof.
Hi Ed, I am about to re-do my roof and glad I read this. Is there any option for getting some insulation factor with a shingle roof? I am in the caribbean where the ac bill kills us! From what I have read here, it would seem that I would need to change to a metal roof of some sort so that the space can be created. Would the space then cause the roof to lift easier with a hurricane? Thanks, Lisa
Lisa,
I would look to either installing Radiant Barrier AtticFoil inside the attic or radiant barrier under a metal or tile roof. I would look to the different roofing products as to uplift data.
I have an attic with vaulted ceilings that does not allow much room to install a radiant barrier though a good portion of my home. I can do approximately about 30% of my attic. Would this be worth the time and effort? Thanks.
Jason
Jason,
Radiant Barrier has a cumulative effect. Doing part will still give a benefit. You will not see the same results as if you could get 100% coverage, but it is still probably worth the effort. Here is a video on Does Partial Coverage With Radiant Barrier Work?
I’m getting ready to put a new metal roof on my house.I currently have clay tile with no radient barrier or insulation. Needless to say my house gets quite hot in the summer. I have no attic it’s all backed up against drywall. I’m installing new sheathing with sharkskin ultra radient, then a batten system with stone coated metal on top. My question is should I be throwing any type of insulation in between the rafters while the old plywood is off. I won’t be able to do it later because its all coverd with drywall. If so what kind of insulation should I use. Thanks
If there is NO insulation between the sheetrock and the roof deck (between the rafters) then you should definitely add insulation before putting a new roof on. As for the metal roof, I would install AtticFoil Radiant Barrier below the metal roof. Here are instruction on how to Install A Radiant Barrier Under A Metal Roof.
I have a sealed cathedral ceiling in my log cabin and would like more insulation or radiant prtection,the roof is rafters with insulation and plywood on top then shingles,do I have to pull off the plywood to install a radiant barrier or is there a panel that I can put over the plywood then reshingle?
You are pretty limited in your options. One option is to do what I did on my home. Basically, I have two roof decks. The top deck has shingles on top and the bottom deck has foam on the bottom. They are separated by 2″ furring strips and I used two layers of foil. Here is the page on How To Install A Radiant Barrier With Foam Insulation.