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Community and Q&A

Closed-cell spray foam on the outside of exterior block wall

nwebster | Posted in GBA Pro Help on

I have recently purchased a home in south western Ontario (Zone 5A) with an addition built over a crawl space in one section of the house.  I would like to insulate the walls of the crawl space better and there is very little clearance under the floor of the crawl space and would be extremely difficult spray foam the walls from the inside.  My question is;  Can I spray foam directly onto the block wall from the outside which would be exposed to the elements.  I am not concerned with aesthetics as there is a large deck covering the block wall and it would never be seen.  I am just wondering if spray foam needs to be protected from the elements such as rain, snow, insects, rodents etc.
Is this method recommended? safe? functional? Thanks

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  1. Expert Member
    Dana Dorsett | | #1

    At 3lbs per cubic foot density closed cell foam is water proof and fairly rugged, a common density for polyurethane foam roofing.

    At 2lbs (the typical density range when used primarily for insulation) it's not bad either. Polyurethane will break down under ultraviolet light, so it needs to be protected from sunlight.

  2. GBA Editor
    Martin Holladay | | #2

    N. Webster,
    If I were you, I would cover the cured spray foam with metal lathe (or chicken wire) and stucco.

  3. nwebster | | #3

    Thanks for the information and advice!

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