Page 30 - Green Builder Remodeling Field Report 2021

REVISION HOUSE SCOTTSDALE PROJECT

Exterior Insulation

Proves Essential to Cut

Cooling Costs Adding a layer of rigid foam dramatically

improves resistance to extreme heat.

BY STEVE EASLEY zones 4 and above, and for good reason.
The decision to add a layer of poly-iso foam sheathing Take for example a typical 2x4 inch, R-13 wall. You have two
attached to the outside of walls at the Scottsdale ReVISION problems: First, the wall is so thin that the maximum amount
House didn’t come about by accident. Last year, the region of insulation you can put between the studs is about 3.5”.
had 145 days with temperatures over 100 degrees Fahren- Second, wood is a poor insulator. Most walls are about 25
heit, including 53 days over 110 degrees and 13 days over 115 percent wood, so a stick-framed wall insulated to R-13 may
degrees. The air conditioner at the Scottsdale house (prior to only offer R -10 overall performance at best (and that’s not
renovation) ran for 14- 18 hours a day, yet the home could not even considering the impact of windows and doors).
be cooled below 84 degrees inside.
Most homes in Arizona and California have stucco cladding A THERMAX SOLUTION
and concrete tile roofs, both of which have a lot of thermal The best way to solve this poor performance is with exterior
mass. The sun bakes down all day on the stucco and tile, and insulation. For the Scottsdale rebuild, we selected DuPont’s
these materials absorb that heat. This heat then transfers into Thermax (ci) insulation, because it added an additional R-10
the house well into the evening hours, long after the sun goes of insulation for my walls, with just a 1.55-inch-thick poly-iso
down. This near constant heat has a huge impact on comfort foam board. Obviously, this can be more of a challenge for
and air conditioner run times. remodels where you want to leave the outer cladding intact.
Exterior foam sheathing has been shown to greatly mitigate For this project, much of it involving tearing down and
this heat flow, so much so that most building codes have rebuilding—however, we had the freedom to do it right. One
required exterior insulation in climate zones 6 and above for concern with using exterior foam is putting an impermeable
years. The 2021 IECC will require exterior insulation in climate product over wood-based sheathing. If water gets between

30 GREEN BUILDER REMODELING FIELD REPORT