I need some advice-
The house I built this summer has a perimeter footing which goes below frost level, and a 5 1/2 inch slab floor in the daylight basement. I was planning in insulating the basement (main floors and roof are SIP’s) and getting utilities hooked up next summer, which means leaving the house cold this winter. My concern is that, without any heat in the house, the ground under the slab will heave from frost and ruin the slab. As far as I know, I have two options:
1. I could insulate the basement as best I can, install a propane shop/garage heater, and set it on 40 degrees to prevent frost.
2. I could layer salt hay and poly sheets to prevent it from freezing. I really don’t know how this is done, much less why it works. Any thoughts?
Adding to the situation is the fact that the house is in Vermont’s Northeast Kingdom (very cold), and I will be able to visit the house only once every two weeks this winter, on average.
Any ideas on how I can protect my floor?
Replies
Nobody wants to touch this one?
Mike
I've thought it about some over the last day or so, but really don't think I can add value. I've never heard of the straw thing, though I can see that decaying stray would generate heat - possibly the reason it works.
Is the concrete laid directly on the dirt? My guess is that dirt with no excessive moisture would not heave your concrete slab. Way up North the soils are pretty stable right? Here in NC we have clay soils that have high expansion rates when wet.
On the other hand, the propane heater on 40 would give you some amount of peace of mind. Is 40 enough to keep the ground under the slab from freezing? Probably. Have you computed how much it will cost you to run that propane for the winter? If it's $100 to protect a $5000 concrete job - that sounds pretty minimal.
Have I answered any questions or just generated more?
I pretty sure if I were in your shoes, I would just let it ride the winter.
MERC.
If you have compacted mineral soils under slab and a daylight drain there is no reason to worry. There will be no water contained in the ground to freeze and heave.
But if you poured right on clay and didn't run drainage, you have reason to worry and to want heat or to stack n a truckload of hay.
Since this is underground and the house itself sheilds from elements, I would expect to see temps down below twenty for more than a few weeks before frost would set in deep enough to be a concern.
Excellence is its own reward!
Thanks for the advice. The slab is sitting on 3-4 inches of compacted sand/gravel, which is over good draining soil on one end of the house and rock ledge at the other end. It is hard to know what to do, and I want to be safe without going overboard.
Thanks again- Mike
The salt hay is a modestly effective but fairly cheap insulator. The poly is to keep it dry, because wet hay is much less effective than dry hay.
How much you need depends on the design frost depth and the relative R values for hay and dirt. I don't have any idea what these numbers actually are, but for example, if the frost line is 60 inches and the R value of hay is twice the R value of dirt, you'd need 30 inches. I would guess that hay is a lot more than twice as good an insulator as dirt, but maybe not 10 times as good.
Another option would be to refill the basement with dirt to the frost line depth. :)