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Community and Q&A

Crawl space with dirt floor and spray foam

Paul Staffieri | Posted in Energy Efficiency and Durability on

I have a crawl space that is covered by walls wood and parchment. Above it is the kitchen hence there are kitchen pipes there that never froze. My garden hose supply line has frozen a couple of times in the past. There is also force air duct work in there. I brought in a number of different insulators and there is no consistency.

1. I’m worried about the moisture and bugs that come up from the dirt floor. There is mold on some of the joists. One insulator recommended that I spray foam the dirt floor with an R10 2 pound spray foam. This will reduce the moisture. Is this a wise thing to do for an extra $300? Or is sheeting better? I also was advised that sheeting causes mold.

2. If I spray the ceiling of the crawl space and pipes I’m worried that the pipes were being kept warm from the heat of the duct work, floor above the crawl space and the dirt floor. It’s unheated unventilated so if I spray foam the ceiling of the crawl space will the pipes freeze?
I want the ceiling insulated and not the side walls as I want to add a vapor barrier in the form of closed cell foam.

3. If I were to spray foam the dirt floor side walls and ceiling of the crawl space that was unheated would this create any issues ie condensation?

I’m in Canada just north of Buffalo so I think I’m in a 6B area.

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  1. GBA Editor
    Martin Holladay | | #1

    I don't know what "walls wood and parchment" means. Except for that, I think that I understand your situation.

    You need to install a layer of heavy polyethylene on the dirt floor, insulate your crawl space walls (not the ceiling), and do your best to lower the humidity level down there. Installing insulation on top of the dirt floor is optional, and is not as important as the other measures I listed.

    The necessary steps are explained in this article: Building an Unvented Crawl Space.

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