Insulation and roofing in the desert
scottsdale95
| Posted in Energy, Heating & Insulation on
All, I am building a new home in the desert — Scottsdale — and need professional input on insulation and roofing.
With 2×6 exterior walls and 12″ flat roof, the house is currently spec’d for batten insulation. I sense spray foam may be a better option, but I see it being used in cold climates on home shows. What would you recommend as the “best” option from an insulating point of view?
On the roofing, the house is spec’d for spray foam, but I have read a number of threads suggesting their are better routes to go. What is the longest lasting, low maintenance way to go for a flat roof in the hot desert?
Thanks!
Replies
Assuming that
your primary goal is to reduce air conditioning loads, a couple of things.
Solar heat gain thru your windows is going to be a huge factor. If you have large windows that receive a lot of sunlight, you should be absolutely sure you understand glass coatings and how windows perform, otherwise there is little to do with wall/roof insulation that will help you.
Walls... I assume you mean batt insulation, not batten. Fiberglass batts are rarely a good choice, IMO. They are not usually installed well, and have other issues. I prefer blown in FG or preferably cellulose. Spray foam works well in walls but the exterior water details have to be impeccable. You could also consider a combination of fiber insulation in the stud bays and rigid insulation board outside the sheathing.
A reflective roof covering is very important. Rejecting some of the solar energy in the first place is critical. Insulation slows down heat transfer but it does not stop it. Closed cell spray foam has higher R value than fiber insulation but you have to understand the other possible issues with foam.
Whatever the choice in walls ... make sure it is installed properly if you use batt insulation. That is critical for best performance.
Roof ... suggest rigid insulation on the roof deck and a 'cool roof' roofing (certified). Avoid batt insulation for the roof if you possibly can.
The other guy is right ... your windows are most critical ... hope you designed the layout good. For east, west, and UNPROTECTED south windows suggest the lowest SHGC possible ... e.g. 0.25 and lower and the lowest U-value you care to afford.