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Can my shallow crawl space be converted to a slab foundation?
I recently bought a 100 year old small stone house a few hundred meters from the shore of Georgian Bay. It has a shallow crawl space which is about 20" deep. About 15 years ago the floor joists were replaced due to rot, concrete footings poured and the floor of the crawl space covered in crushed stone. I have high humidity in the house and crawl space (despite the fact that the crawlspace is always clean and dry) for which I am trying to find a solution. And no doubt need some radon mitigation as well. The house is sitting above bedrock and my neighbour who tried to dig a basement found water at about 42" below ground level. These constraints seem to have ruled out a lot of possibilities. Would it be realistic to look at converting to a slab foundation and how might I go about it?
Yes, you can convert a crawl space into a slab on grade foundation, it just isn’t a particularly cheap process. You would need to jack the building up, and depending on the situation either remove the existing foundation or fill it in, then pour a slab on grade and rest the house back down on it. We of course can’t give you any specific advice on how to carry it out, you would be best to consult a local engineer or general contractor for that. If you have a high water table I would suggest a raft slab that has no footing and spreads the weight evenly over the whole surface, so you don’t need to dig as deep. That way you can avoid any issues with drainage while trying to build the footing.
If that turns out to be too costly, remember that you can repair crawlspaces in most cases, see here for more info on that option, as well as how to mitigate radon gas –
How to insulate crawl spaces properly
How to remove radon gas from basements and crawl spaces