What is the best way to add radiant barrier to a roof? Is it ever advantageous to install a foil below the rafters after the roof is installed? And if the roof is already installed, is foil sheeting better than a spray application?
A radiant barrier installed under roof shingles will offer no thermal benefit. As to which is better, a radiant barrier sheet or spray on IRCC (interior radiation control coating) – generally, a properly installed radiant barrier will outperform a spray on IRCC. However, the specific application needs to be taken into consideration, for if it isn’t possible to install the sheet material over the entire roof area, the IRCC could be the better choice. Also, it is important to be certain that the quality of the IRCC is good. I suggest you contact a RIMA-I member that handles those products to insure you are getting the best. You can also discuss with any of them the issues you raise and they will guide you to the best option.