What makes more sense, insulating crawl space vs. under the floor?
According to this page:http://energy.gov/energysaver/articles/where-insulate-home
there are about 3 ways of insulating the bottom of a house... If the house is built on grade, you insulate the sides of the slab and possibly underneath the slab.
If the house is built so that there is a crawl space, the crawl space can be of the ventilated type where the underfloor of the house is insulated with fiberglass batts or spray foam.
The final way is to make the crawl space into an unventilated crawl space, i.e. a "conditioned space" place a plastic sheets all around, make provisions for drainage around the foundation, either outside or inside for excess moisture, seal off everything, then have a light duty ventilation system for Radon, then insulate the foundation walls instead of insulating under the floor. The primary benefit of this supposedly is that you can use much more insulation around the foundation walls, and get more of the house envelop insulated for lower cost vs. just between the joists in the house.
So I guess my question is, the idea of turning the crawlspace into a "conditioned space", is that really better than insulating underneath the floor, between the joists? I live in Northern California (SF Bay area) and the ground temperature isn't all that warm, if anything a bit chilly. So if I insulate the foundation but not the ground itself, turning the crawlspace into a conditioned space, wouldn't the cold from the earth seep into the house, making the house cold? Yes there is a plastic sheet so there shouldn't be any air movement and while I should really being looking at this from the perspective that it's the heat that is moving to a cold space, not the other way around, wouldn't the same still apply? That the earth would absorb the heat from the conditioned space, making the place effectively colder?
I have an older house that I want to retrofit that has zero insulation in the floor and I'm trying to decide whether it's a better idea to insulate the floor vs sealing off the crawl space and insulating the foundation instead.
Posted Feb 8, 2013 8:42 PM ET
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