Barely vented, uninsulated, bedrock crawlspace vapour considerations. – GreenBuildingAdvisor

Evening all.

I’m working on a 1970s extension of a 1970s home. House is on bedrock, and the extension appears to be as well. The extension crawlspace is not part of the main house crawlspace. As I’m renovating the walls from the interior to complete a tattered vapour barrier, I’m trying to decide how to handle the crawlspace and floor.

Best I can tell, the (very short) crawlspace is bedrock/dirt without any vapour barrier. The foundation walls have the rim joists rabbeted (for lack of a better term) into them, the foundation rises above the floor by about two inches, and the toe plates of the walls therefore are the sill plate. The crawlspace historically has had a very serious rat problem. Though that’s taken care of now, I don’t want to spend too much time down there 🙂

The floor joists are subfloored with…. Particle board 😞. Over that is 3/4″ply. The poor drainage causing moisture ingress (being dealt with this coming spring) and probably the rats has contributed to the particle board (where we’ve seen it) being in a sorry state or totally gone in places. Short of tearing up the entire floor, I was thinking of trying to get down there and add a 6mil poly vapour barrier to the floor, and then bring it up the foundation to attach just below the “rim” joists (which as previously mentioned, don’t actually support the walls, just the floor.

Insulating from the outside is possibly a spring project, but I’m hoping to make improvements to the crawlspace and or floor this winter. Interested to hear your thoughts. Thanks in advance.