There are at least two things worth nothing about the house that Satinder is building in climate zone 4A.
“I am building a house in flood zone over a crawlspace that has flood vents,” he writes in this recent Q&A post. “It has already been constructed with a poured concrete foundation and a 3-inch concrete floor over a vapor barrier.” (Flood vents are designed to equalize hydrostatic pressure in flood zones; for more see this FEMA bulletin.)
Drains have been installed below the concrete slab, and the crawlspace also has a sump pump and a radon mitigation system. Satinder’s concern is how to insulate and air-seal the crawlspace to prevent cold floors in the rooms above, and to prevent air leakage into the living area.
An insulation contractor is recommending 3 inches of closed-cell spray foam on the crawlspace ceiling, plus 2 in. of foam over the rim joists. That would provide almost R-20 worth of insulation in the crawlspace ceiling and another R-13 on the rim joists.
“Is this going to be enough to separate the crawlspace from my living space from temperature fluctuations?” Satinder asks. “Is this going to create any issues with water condensation during summer since it gets quite humid where I am.”
Those concerns are where we start this Q&A Spotlight.
Is spray foam the best option?
Closed-cell spray polyurethane foam has advantages. In addition to high R-value per inch, it also blocks the passage of water vapor, and it’s a very effective air barrier. Does that make it the best choice here, as Satinder’s contractor is suggesting?
Not necessarily, says Steve Knapp. He refers Satinder to an article from Fine Homebuilding on insulating this type of assembly, and points out that there are ways of insulating cold floors that…