Foil Under Shingles Will Not Work Unless There Is An Airspace On One Side Of The Foil.

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

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 Before Installing Standing Seam Metal Roof

Foil Installed Under Roof Using Battens To Create Air Space

Foil Installed Under Roof Using Battens To Create Air Space

Foil Installed Before Metal Shingles With 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:

  • Installing Radiant Barrier Over Spray Foam Insulation
  • Introducing WareHouseFoil.com – for Commercial Applications
  • Enerflex® Radiant Barrier at Home Depot compared to AtticFoil® Radiant Barrier
  • Radiant Barrier Installation Summary – Block the Heat
  • Techshield Compared To AtticFoil® Radiant Barrier
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    39 Comments to “Radiant Barrier Under Shingles – Scams & Bad Information”

    1. Danny Williams says:

      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

      • Ed Fritz says:

        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.

    2. Jeff W says:

      So I’m confused. Radiant Barriers do work but only on the inside of the attic then?

    3. Dante says:

      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.

    4. LakewoodDad says:

      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.

      • Ed Fritz says:

        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.

    5. Audrey says:

      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 :(

      • Ed says:

        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.

      • Craig M says:

        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

        • Ed Fritz says:

          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.

    6. Robert says:

      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.

      • Ed Fritz says:

        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.

    7. jerry says:

      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

      • Ed Fritz says:

        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.

    8. Lisa says:

      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

    9. Jason says:

      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

    10. Charles says:

      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

    11. gary says:

      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?

    12. David Carroll says:

      My friends condo I have been staying at has vaulted ceilings, with exposed beams. The ceiling is actually 2×6 T&G, this also is actually the roof decking also the is 1″ of blue Styrofoam board with a torch down roll roofing on top, the roof needs replacement as it is leaking.
      This is in Anchorage, Alaska where we get a considerable annual snowfall. The owner is going to replace the roof and wants to know what he can do to increase the “R” factor. the problem is that there is a serious “Glaciation” effect and the heat bills are completely off the chart. Any suggestions???

    13. jason says:

      Ed,

      Great site! Thanks!

      I am getting ready to re-roof. it is an old home (1911) with flat roof dormers. I am considering applying some of your designs to the flat dormer and non-vented area.

      1) wood deck
      2) underlayment (synthetic? felt? or ice and water shield? or does it really matter?)
      3) radient barrier
      4) furring strips
      5) Tech shield
      6) underlayment – Ice and water since it is flat roof
      8) flat roofing – most likely white if I can get it.
      9) FasciaVent with a ridge vent for venting the new deck — http://www.dciproducts.com/html/fasciavent.htm

      I would apply insulation on the inside of the roof between the deck and sheetrock. Would you suggest foam or fiberglass? my concern is foam may create moisture problems. What do you think? And is there anything else I should consider

      It is a hipped roof and I am also considering putting in a SmartVent at the eve so that I do not have to cut up may 100 year old beadboard sofits. — http://dciproducts.com/html/smartvent_eave.htm

      I would continue to use the turbines as the exhaust.

      Do you have any experience with SmartVent or FaciaVent? I realize they are not your products, but thought you might have some insight.

      My only other concern is tying in the 2.5″ second deck to the remaining single deck. Essentially half of the house consists of the dormer and cathedral ceilings and the other half is open attic. I assume it would be ok to make some kind of wedge to make a gradual transition from 2.5″ to 0. It is only a 6 ft section on each side of the ridge

      Thanks again

      • Ed Fritz says:

        Jason,

        This looks like a well though out plan, and I like it. I don’t think you really need the underlayment over the bottom deck. I would go with only one waterproofing layer to the outside under the roof. Or go with a membrane type roof like http://www.Duro-Last and eliminate it all together.

        As for insulation, if it’s airtight, foam or fiberglass will do. Just make sure you seal it up tight. I like edge vents – there are several brands and I have had several customers use them with good results. You should be able to make the transition in roof elevation without any big issues.

    14. tina says:

      is Solarhide made by EcoChiefProducts.com any different from these other foil barriers? Their brochure states that it is a Radiant and thermal barrier.

      • Ed Fritz says:

        Tina,

        This is the information directly copied from their website:

        “SOLARHIDE is Eco Chief’s energy saving roofing underlayment. When SOLARHIDE is properly installed in the roof system with the foil side facing an air space it acts as an energy saving radiant barrier. If SOLARHIDE is installed under composition shingles with the foil side facing down on the roof deck its an effective thermal barrier that reduces heat gain in to the attic of a home.”

        I agree that IF the foil is facing up and facing an airspace typically seen in tile and metal roof applications, then it WILL act as a radiant barrier. I go into full details here on How To Install A Radiant Barrier Under A Metal Roof.

        The part about the foil facing down is a little confusing. What exactly IS a THERMAL BARRIER? If you look up the definition of a “Thermal Barrier” it says “(Engineering / Aeronautics) an obstacle to flight at very high speeds as a result of the heating effect of air friction Also called heat barrier” or “Noun – thermal barrier – a limit to high speed flight imposed by aerodynamic heating”. I’m sure this product has nothing to do with the speed of an airplane going through the air. I would ask them where they got this term and what it means because in roofing and building science community I have never heard the term used. Normally, heat resistance is measured in R-Value, they do not state any r-value. I could not find any specific specifications listed, but most roofing underlayments are about 1/8″ thick and there R-Value would be less 1 and Foil really has no r-value, in fact it is a great conductor of heat when installed (sandwiched) between two other products.

        Since you need an airspace to have radiant heat and therefore have a radiant barrier, and installing ANY foil (AtticFoil included) product directly between two products will make the foil a CONDUCTOR, the foil will not help reduce heat flow and more than the product it is attached too.

    15. Amber says:

      Hi Ed,
      Been researching the last six months what to do about our roof that needs replacing. We live in the Sacramento Valley, hot days and cool evenings (usually).

      We have cathedral vaulted ceilings throughout the entire one story house – mostly NO ATTIC. Our current roof configuration is this: Tounge/groove ceiling, 1/2″ ply, 2″ Polyiso (Celotex Thermax) with reflective foil covering both sides, another 1/2″ ply, felt and finally comp shingle. We have no existing grid or frame system OR venting system. We bake in the summer and freeze in the winter.

      A small section of our hallway has some attic space – so we added a whole house fan earlier this year.

      Due to cost, we will have to shingle using a cool roof comp. Obviously we will need some sort of ventilation and it looks like the 2X2 batten system would be best. What is the best way to incorporate your radiant barrier with using comp?

      Thank you so much for your time.

    16. Ken says:

      I have a roof that i need to replace the singles on. It is a dormer set up, so very little insulation and no space to add any more. Can i use something like you describe in this with 3 tab asphalt singles?

    17. Ed says:

      What do you think about builders who don’t install the right amount of insulation in a home? Our specs call for R19 in exposed walls. The builders install R11. The walls are only 6″ face to face whereas the proper walls would be 8″ IF they install insulation at all. They install foam board which only has about a factor of R3.33. Heat or cool air comes out of our outlets. Place a pillow against the inside of an exposed wall and in a few hours, pull it away and it will be hot in the Summer and cold in the Winter on the side of the pillow against the wall.

      • Ed says:

        Well first it depends on where you live and secondly, the effective R-value of a framed wall assembly with insulation is always less than the R-value of the insulation alone, since you have to take in to account thermal bridging through the studs, which lessens the performance of the wall. Foam should be added to walls in a way that makes the installation air tight, to be most effective. Unfortunately, it’s hard to monitor how builders are installing the insulation and to ensure they are doing every step 100% correctly. If you are concerned that you did not receive what the contract outlined, then I would suggest contacting your builder and perhaps a home energy auditor as well.

    18. Lex Gillean says:

      Ed Fritz,
      My new Gerard metal roof was applied with battons & Solarhide on deck but with foil side down (will I get “any” benefit at all with it other than some water proofing ?? your opinion please!!!!!)
      What can I do in my attic now that may help me? My attic is 14 ft. tall and accessible with 6 inches blown in insulation , 24 soffit vents, electric gable vent & 6 roof vents. 3200 sq. feet, single level
      I’m in Texas near Lubbock in lower Panhandle. We’re 101 degrees today.
      Thank you!!!!!

      • Ed Fritz says:

        With the foil facing down all you are gonna get is the underlayment (waterproofing) qualities. I’m curious if a roofing company did this? If so, you may have some recourse since their install instructions clearly state that the metallic surface must face an airspace.

        If you want do reduce the radiant heat flow, simply install by stapling up in the attic. You will see a huge difference. Ranch style homes in the South are the best case for best results. I’d also turn off the fans. Fans and roof vents don’t work well together. See my post here: Attic Ventilation – Don’t Mess It Up.

    19. D says:

      How about Lowe Therma Sheet? Various roofers want to put it under the underlayment for a roofing job. There is a layer of foam between sheets, does that create enough airspace?

      Thanks!

      • Ed says:

        No, foam is not an air space. An air space (or gap) would be a space that is void of any matter, meaning the only thing that can be in the space is air itself. Not airy items, or items that have air injected into them, just air. Without air, there is no radiant heat transfer and it’s a bogus claim.

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