Foil Under Shingles Will Not Work 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 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 products like Polaralum® and other types of foil coated roofing underlayments as radiant barriers. This following quote is from the manufacturer’s website: “During Summer Months Polaralum® acts as a radiant barrier on walls, and thermal barrier on roofing areas”.
Excerpt From a Manufacturer of Polaralum
Notice how they say “THERMAL Barrier” not “RADIANT BARRIER” under the roofing. Yes, this product is a thermal barrier. In fact, a sheet of notebook paper is a thermal barrier to some extent. The manufacturer states it correctly. It is NOT a radiant barrier if installed under (normal) roofing shingles. Somehow roofing companies are misinterpreting this and selling it as a “Radiant Barrier” for this application.
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 get ready. Customers & lawyers will be calling you soon starting with my neighbor who just got scammed.
If you are a roofing company who knowingly has been doing this – Shame on you. I hope you get sued and you go out of business.
If you are a roofing company and have done this by mistake – Contact the homeowners, and make good on your mistakes.
If you are a lawyer, feel free to go after the first group of roofers – it should be like shooting fish in a barrel and send me a referral fee. It will be impossible for them to find a lawyer who can defend them since the definition of radiant heat is pretty indisputable.
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 the low-cost roofing felt, 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, Polaralum, Polaralum Radiant Barrier
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 as Polaraum suggest. By the way their product is applied between the felt paper and the shingles with the foil side down on the felt and the white felt side up facing the shingles. 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?