[Greenbuilding] Desert roofs

[Bruce Donelson]

We're still designing this new house in Phoenix, trying to price
workable systems. Our three options for roofing are:

1. Pale-colored metal roof. I'd use regular galvanized, but I'm
concerned that the low emissivity of unpainted metal will inhibit
cooling after dark--any thoughts on this?  The paint increases the
reflectivity somewhat too.  The metal roof would go on 2x4 sleepers
over a membrane and structural deck, creating a vented 3.5" airspace.



There is a tax credit available for "cool roofs".  These metal roofs have a
low absorption because of the use of micro spherical ceraimic beads that
reflect light. Some of these colors are pretty dark.

Elk makes a composite shingle using this technology, but the absorption is
too high to qualify for the tax credit. The shingles do stay cooler in the
sun. Not cheap, approx $90/SQ.

Bruce Donelson
A Better Builder