I live in St. Pete, FL, and want to know more about closed-cell foam insulation for my crawlspace. Is it safe to use?

Asked by David Deering
Saint Petersburg, FL

The house is hot and moist during summer, freezing in winter, and I believe most of it is due to the crawlspace. House was built in the '50s.


Polly Osborne, FAIA, LEED AP

Answered by Polly Osborne, FAIA, LEED AP

Los Angeles, CA

Polly Osborne Architects

December 16, 2010

Even in dry climates, you'd be amazed how much moisture comes through the floor.

I think closed cell insulation might be ok, but when I think about using it I always ask the question: is moisture going to get trapped by it? Human habitat has moisture that could get trapped in, and possibly harm, the floor joists, but I hope someone else will weigh in on this, too.

My first thought, and it is cheaper than home foam insulation, is to:

  • lay a vapor barrier in the crawlspace,
  • run it up the foundation walls and seal it,
  • then add positive ventilation in the crawlspace with a small fan built for this purpose,
  • then insulate the floor with any insulation that is designed to fit between joists, such as cotton batts or formaldehyde-free fiberglass, or cellulose in a netted installation.


For more information:

Read Florian Speier's Q&A "We have an unheated crawlspace under our house that we would like to insulate."

Also, read Danny Kelly's Q&A "What kind of waterproofing can you use in crawlspaces to help with going green?"

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