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Crawl space insulation installation. Bids include spray foam and fiberglass

barrierinstall | Posted in Energy Efficiency and Durability on

Home built in 1962, without insulation in crawl space below the floors. I have bids for R-19 closed cell spray foam, or fiberglass. The area is Seattle. Any advice? Thanks.

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  1. GBA Editor
    Martin Holladay | | #1

    I don't think that fiberglass insulation is an appropriate insulation material for crawl spaces, so I would urge you to install the spray foam.

    For more information, see Building an Unvented Crawl Space.

    In most cases, it makes more sense to insulate crawl space walls than it does to insulate between the floor joists. If you end up insulating between the floor joists, however, you should know that in your climate zone (Marine 4), the building code (for example, the 2009 IRC) requires a minimum of R-30 for floor insulation -- not the R-19 that your insulation contractor is proposing.

  2. davidmeiland | | #2

    Are these bids for insulating the joists, or the crawl space walls?

    If you're insulating the joists, I'll differ from Martin, who does not seem deterred by the many stories we read about spray foam that didn't adhere completely to the framing, shrunk away from the framing after installation, has air channels through it, and so on. Of course, many installations are probably fine.

    If you're insulating the walls, you might consider rigid foam.

    I insulated my joists with cellulose. First we air-sealed the entire floor, then installed a heavy fabric called "canvex", then dense-packed the whole thing. As far as I can tell it worked very well. We are currently doing another house in a similar manner. I don't have good access to a spray foam installer so it's not much of an option for me.

    Martin is correct re the code requirement, but that doesn't generally apply to retrofit work, at least here, where the inspector will accept insulation installed to the full depth of the framing. If you have a 2x8 floor frame you can get roughly R-25 with cellulose.

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