Ted has more than a few cobwebs in his attic. The unconditioned space also houses his HVAC system.
The 1,800-square-foot brick ranch in Climate Zone 4 dates from the 1960s, but the previous owner installed both a furnace and ductwork in the attic just four years ago. Ted also has inherited a powered attic ventilator. Although both the attic floor and the ductwork are insulated, Ted recognizes the situation isn’t ideal.
Summer hasn’t even arrived, he notes in a post at GBA’s Q&A forum, and when the temperature outside climbs to more than 95°F, the temperature in the attic tops 120°F. That has kept the ventilator working, but Ted surmises the high temperatures are reducing the efficiency of his air conditioning equipment.
“Should I turn off the ventilator so it won’t suck cool air from the conditioned area?” Ted asks. “Should I put more insulation material on top of the attic floor and the ductwork? Will a radiant barrier under the rafters help?”
Those are the questions to get this Q&A Spotlight rolling.
Add more insulation
Dana Dorsett would have Ted get the level of insulation much closer to the R-49 recommended in the International Residential Code.
“In a DOE Climate Zone 7 (not to be confused with a USDA plant hardiness zone 7) a mere 8 inches of fluff is woefully inadequate,” Dorsett says. “IRC code-minimum for zone 7 is R-49, and you have barely half that. Air sealing all the ducts and air handler connections and seams, and air sealing all the duct boots to the ceiling gypsum (and any other penetrations) is a critical first step prior to adding any insulation.”
(As it turns out, Ted initially confused the two climate zone designations. His house is located in DOE Climate Zone 4,…