Joe Watson lives in a three-story 1993 house in Richmond, Virgina, with a walkup attic, part of which he’d like to turn into living space. The question is how.
“I am looking to insulate all the rafters and bring the HVAC into semi-conditioned space,” he writes in a Q&A post at GreenBuildingAdvisor. “I would get a minisplit system for the 20×20 room that would be drywalled in on the third floor. (The rest of the attic space would be left unfinished with a fire barrier of the insulation).”
He’s been told that R-30 will be adequate for his Climate Zone 4 home, and Watson so far is looking at two insulation options: fiberglass batts and spray foam.
“If I go fiberglass, I would attach 2x4s to the 2×8 rafters to give me a space of 10.75 inches to add insulation and leave a gap for a vent from soffit to ridge,” Watson says. “If I go spray foam (professionally done only) I am unsure on open-cell vs. closed-cell in my climate zone. Two of the three quotes I got said open-cell, but could do closed-cell for more $$$ (shocker). I get my third quote tomorrow.
“After reading so many posts/blogs/articles, I am lost on the open-cell vs. closed-cell question for my area,” he continues. “We get really hot in the summer, and, last winter hit the low teens at night (unusual, though). Any thoughts?”
That’s the topic for this Q&A Spotlight.
R-30 worth of insulation just isn’t enough
No matter what his local building office says, Watson’s climate zone calls for more insulation than R-30, says GBA senior editor Martin Holladay. “In your climate zone,” he writes, “the 2012 International Residential Code calls for a minimum of R-49 roof insulation — so even if your…