Q: I just bought my first house and am about to remodel my basement. The previous owners of the house glued 2-inch-thick foam insulation to the poured concrete walls. It’s got an aluminum foil face on it. Then they covered that with an open-cell foam board that’s 3/4-inch thick.
It seemed the smart thing to do is tear all this off, and I started to do just that. But then I thought to ask you before I go any further. The foam board seems to be in the way of installing the electric wires that I know are supposed to be behind the insulation. What’s the best way to deal with this situation?
A: You definitely don’t want to tear any of that insulation off the walls. The previous owners made a fantastic investment by putting all that foam on the frigid poured concrete walls. The use of foil-faced foam was even smarter. It’s a radiant barrier and bounces heat back to its source.
The only mistake I feel they made was adding the extra layer of open-cell foam over the foil-faced insulation. This will reduce the ability of the foil to bounce the heat of the basement back into the space.
If I were you, I’d start to frame the walls using either 2-by-3s or 2-by-4s. I’d create an air gap of about 3/4-inch between the back of the wall studs and the foam insulation.
This air gap serves two purposes. First, it allows you to create plumb walls should the poured concrete be out of plumb. Second, the air space is a place for any rogue condensation to evaporate.
When I finished the basement of my last home in Cincinnati, I did what I just described, but there was no foam glued to my poured concrete foundation. I used regular fiberglass batts in the wall-stud cavities to insulate the room. Before adding drywall, I covered the walls with a 4-millimeter vapor barrier. The 3/4-inch air gap between the back of the studs and the concrete helped prevent mold and mildew growth should a tiny amount of moist room air make it behind the insulation.
You should never have a condensation issue because the foil-faced foam you described is a great vapor barrier. As long as the seams between each sheet are sealed with aluminum tape and the gap at the floor is caulked, no moist room air can get to the cold concrete.
As for how the electric cables and wires are installed, I’d never want mine to be touching the poured concrete walls. You could drill holes in the center of the wood studs and pull the cables between boxes just as you would in any normal interior or exterior wall of a home. My advice to search online for videos made by the authors of the National Electrical Code and soak up all of their useful information.
Tim Carter has worked as a home-improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.