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Open vs Closed Cell in Crawl Space

Mark Moses | Posted in General Questions on

I hate to ask this question b/c I feel like it has been well covered on this site and at BSC…. but I’m getting some conflicting information from the local experts.

The details are; 100 year old balloon framed townhome in zone 4A. A couple years ago I put down 20mil vapor barrier in the crawlspace which has limited access and uneven brick and mortar walls. There are no vents and I did installed an exhaust fan (panasonic whispergreen). It has never had standing water issues but does have high humidity in the summer months. I am now going back and finishing the job by insulating (and air sealing) the foundation walls and removing the old pink insulation between the joist. Given that the walls are uneven, my climate zone and access issue restrict rigid foam installation; I think the best option is spray foam on the walls, rim joist and sill plate. It was my understanding that the best practice approach for this option would be Closed Cell SPF.

Just to name a couple ref:
1) http://www.buildingscience.com/docum…sure-guideline Several ref in this very detail document but flow chart 37 is a good one.

2) https://www.greenbuildingadvisor.com/…ed-crawl-space

3) http://www.buildingscience.com/docum…ts?full_view=1

All of the insulation contractors in the area are suggesting OC (I’ve gotten 4 quotes thus far).

So my question is, am I missing something? is ocSPF the way to go for zone 4A?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Mark,
    Closed-cell spray foam makes more sense in this application. It's stronger, and will do a better job of consolidating your uneven walls. It will limit water entry through the walls, which is a good thing. It will also behave better in a moist environment.

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