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.
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.
I've written several other posts on this that you might be interested in. Check these posts below: