1979 Uninsulated Slab Home in Vermont
Hi there,
We are purchasing a home by Mount Mansfield in Vermont at 1400 feet (thus cold in winter 🙂 and it was built in 1979. I presume there was no poly or slab vapor barrier when constructed, nor insulation under/in the slab because of the year built. You can tell that there are moisture issues on the old existing flooring. I’m trying to figure out what to do to improve the energy efficiency, comfort and likely moisture issues. There is baseboard water heat running around almost the entire interior perimeter, which seems like it makes it hard to add any floor height for insulation without lots of moving of plumbing up higher to accommodate (expensive). I have lots of questions swirling in my head: I’m not sure what flooring options I should utilize, so I’m looking for help on whether to add a moisture barrier coating to the top of the slab (which kind?) and then what flooring might be acceptable in these conditions. I’m also wondering if I should try to dig out around the exterior of the slab foundation and add rigid foam (if so, what kind and how thick?). And then any recommendations on a covering for protection of the foam. The home inspector didn’t think adding foam was a good idea, although he also insisted I should just put LVT flooring down with nothing else and call it a day (so I’m not sure how much weight to put in his recommendation). And would it help with slab moisture to add perimter drainage away from the foundation while it’s already dug out potentially? Any help would be much appreciated, thank you!!
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Replies
You need to figure out where the water is coming from because that's going to determine the solution.
In a place like Vermont that gets a lot of snow, with slab-on-grade my first thought would be snow is piling up against the walls in winter and when it melts the meltwater runs under the wall. There's a reason basements and crawl spaces are popular in New England.
Thanks for the reply. I'm sure there is significant snow or water coming off the roof which I can maybe mitigate the rain with gutters as it's a saltbox style with no gutters (and try to shovel snow away from the house, which will be cumbersome), but I was also assuming that a slab with no vapor barrier will pull up moisture from the ground beneath it and around it regardless, correct?
Yeah, but you can't just assume that's the problem. What you describe is called "rising damp," it happens, sure. But your problem could also be condensation in the summer when warm humid air contacts a cold slab. Or it could be snowmelt coming under the walls. Or it could be something else.
Without knowing what the problem is you're just guessing, and it gets expensive to guess wrong.
Constantly damp soils around the perimeter are bound to have a negative impact. I can see no downside (except the hard work involved) in digging a "moat" all around, applying damp proofing, insulation, and making sure there is good drainage. We wouldn't build a slab on grade house today in that climate without those features. So by all means they should be seriously considered.
Thanks so much for the replies! So it sounds like digging the moat and doing the outside work (including gutters to get water away) will make a big difference. Does anyone have thoughts on the interior flooring question given the situation? Do I need to put a coating/vapor barrier before flooring? And is it only safe to use non-absorptive flooring (so no hardwoods/engineered wood for example)? What about any tips on how to do the exterior rigid foam around the foundation? Thanks!