Recommended for all of building exterior (this has a large impact on annual cooling; it is low cost since materials and colors are discretionary and color has little impact on cost). R-19 insulation is adequate in hot climates if the roof is white. Best white roof will be a pitched metal galvalum type which will maintain its reflectance and space cooling by 10% over other options. If a white roof is not specified then adequate attic ventilation (gable/ridge and soffit) should be provided with at least R-30 ceiling insulation and a truss mounted radiant barrier system (RBS). Although they do not provide the performance advantage of a true white roof, light colored shingles (light gray or white) are still preferred although an RBS, added insulation, and good attic ventilation is recommended. Knee-wall insulation in cathedral ceilings should be carefully attached (standard practice falls off of vertical sections).
HOWEVER, this 'quote' makes mention about soffit, gable, and ridge venting. This foiled 'material' actually draws heat FROM THE UNDERSIDE of the sheathing, and 'vents' it into the attic space. From there, it's to be 'transported' out the gable and ridge vents. This would be OK w/me since the heat is DRAWN from the sheathing and, with proper ventilation, transported to the outside. It does NOT 'reflect' heat back through the sheathing.
I guess what I keep saying to myself is, "WHY don't these companies all mention that soffit and ridge/gable vents are necessary?" Some do, some don't. On the surface, an uninformed consumer would think that they could simply paint, or foil, the underside of their attic W/O proper venting. The information on venting is probably buried deep down in the paperwork you get when you buy the barrier or the paint! If the mfgrs. of this stuff told the Homeowner that they need to vent the attic FIRST, how many sales do you think they'd make compared to the number of sales they make when they DON'T inform the consumer, DIRECTLY - In Person - Up Front - etc.?
I have a question or 3 for Wayne: Wayne, if your attic is NOT vented with a soffit - ridge vent system or a soffit - gable vent system, will you pay to have that done first, BEFORE you apply the radiant paint under the sheathing? Or will you go ahead and paint the underside of your sheathing now, and just forget about proper venting? Would you be able to install soffit and ridge/gable vents yourself, or will you have to pay a pro? And if you pay a pro, do you know what it costs?
I'm gonna assume that you can paint the barrier on yourself, but I'm also gonna assume you're not 'comfortable' with installing either of the aforementioned vent-systems. (If you are, great! But then go back and re-read my questions ...) I patiently remain.