Gents…..we going to install a new roof on our home in Houston. The existing is a composite shingle approx 15 years old w/ plywood decking. I’m looking into making our house more energy efficient with the one we install. However, it seems every roofer has a different opinion about what to do to reduce the heat in the attic. So far we have heard about ridge vents, replacing existing plywood decking for high tech thermal decking, and painting the inside of the attic w/ a special paint.
Any other feedback on this????
Replies
Berk, I recommend that you either drape a radiant foil barrier over the roof rafters(shiney side toward living area) before decking, or staple up across the rafters after deck on.(this is easier if you have the attic head room). Install good ridge vents. Channel the air from continuous soffit vents to the ridge vent(or to collar ties) using the radiant barrier as the inside "wall" of the chamber. This will let a convective air current flow between the rafters from soffit to ridge, and will exhaust a huge amount of hot air. It will also keep the heat from radiating into your attic insulation and duct work, if any in the attic. Your goal is to get the attic to outdoor air temp.
It will not cook your shingles. In fact, they will be cooler on the under side, and will not bake half the night from attic stored heat.
You may be able to cut you cooling load 20-30%, depending on house design and duct work placement. Where is your duct work, and does it hang from the rafters as many do in Texas?
The paint they refer to, is a radiant barrier, but no where near as effective as foil, which will block 96+% of radiant heat flow. Also, the paint is quite costly. You can purchase plywood with foil on it, but you lose the air channeling structure of a foil layer across the rafter inner edge. If you have any questions with this, don't hesitate to ask. Paul
I've read a few articles on this over the last few years. I believe most of them were in the Journal of Light Construction. The articles reported on actual testing done by building scientists. If I remember correctly, the foil barrier was very effective, along with ventilation between soffit and ridge. Exactly what Paul said.
There was also discussion of roofing material. White shingles were better than black, of course, but suprisingly not all that good. They tested some new specially made high reflectivity shingles and found them to be much better. They also tested some roofing that was dark, but specially designed to be reflective to infrared energy. Those materials, even though they were dark, reflected more heat than standard white asphalt shingles. So, there are materials available that can substantially reduce heat gain from the hot Houston sun.