Andrew Barss wrote:
I'm looking for advice and ideas for improving energy efficiency in my house,
especially heat from the roof and attic.

I own an older house in Tucson, and we are trying to do what we can to
decrease our electricity (mostly air conditioning) bills. The house has
a peaked roof, with a low attic that has minimal access. The attic has some
blown-in loose insulation between the ceiling joists, and nothing on the
underside of the roof itself (and putting anything there is essentially
impossible). We have some degree of venting -- there are small
vents on the two end walls near the peak, and two passive vents (rotary
type) on the roof, about four feet down from the peak.

I've heard various things, some conflicting, about how to better
the situation:

a) blow in a lot more insulation.
b) increase airflow using soffet vents (aka birdboard).
c) do both
d) do both, but with some sort of a channel up from the soffet
vents to above the insulation.

e) tear the roof off, put a lot of money into a high-tech roof
treatment. The curent roof is light-colored shingles,
and in quite good condition.


Anyone living in the Southwest have advice on what the best move is?

"d", although not the whole story, is probably the closest for old
construction.

Some other things to take into consideration for hot climates:

Vented roofs reduce the total solar heat gain by roughly 3 to 5%.
Consider installing ridge vents instead of the passive rotary vents
along with your vented soffits. Clay or concrete tile shingles can
reduce the solar heat gain by 10 to 15% in a vented roof. Color is not a
big an overall factor as you might think; material is, however. Dark
colored clay or concrete tile shingles outperform light colored asphalt
shingles, but in general light colored roofs do perform better than
dark, although it may not be significant taking material into account.

Radiant barriers can have a significant effect on reducing solar heat
gain on asphalt shingled roofs, not so much on clay or concrete
shingles. Best is a product like "tech-shield" used as decking, better
than none at all is the spray on radiant barrier paint. Keep in mind
that you need at least 1" of void space below the radiant barrier for
maximum effect. Radiant barriers do perform significantly better on
vented roof systems.

Basically, unvented roofs with clay or concrete tile shingles and R-19
insulation or greater; and vented roof systems, with mechanical
equipment and ductwork within the conditioned space, and R-19 or greater
ceiling insulation, perform the best in the Southwest.

If you do decide on "e", your best bet for hot climates is a design that
incorporates AC ductwork and air handlers within the building thermal
barrier, and a vented roof with clay tile or concrete tile shingles and
an R-30 or greater ceiling insulation.

If the AC ductwork and air handlers must be located in the attic spaces,
then go with a design that incorporates an unvented roof, creating a
conditioned attic space for the mechanical equipment.

Do your homework and find some "green" building seminars in your area
.... the woods are full of them.

--
www.e-woodshop.net
Last update: 10/22/08
KarlC@ (the obvious)