Fill crawl space with foam?

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From above, along one of the outside walls, across the ends of the joists, cut a two foot strip out of the floor, then you can drop underneath and put fiberglass batts between each joist. You can then roll a sheet of plastic out and staple it to the bottom off the joists.
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In a heating climate, that would be unwise--the vapor barrier goes on the warm side of the surface.
Wayne
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wrote:

Not on the soil underneath, assuming there was a way to seal the edges where the barrier met the cinder blocks?
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Well, a few comments:
A vapor barrier in the floor system is to keep warm moist air from migrating into the crawl space, condensing there, and causing the usual problems of unwanted water. This should definitely be on the warm side of the insulation; otherwise water vapor will travel through the insulation, cooling as it does, and condense in the insulation, where it would be trapped by the vapor barrier underneath.
A vapor barrier on the soil is to keep moisture in the earth from rising into the crawl space. So it serves a different purpose. If you have a vapor barrier in the floor system, I'm not clear on whether having one on the soil would cause any problems. I'm just wondering how any vapor in the crawl space would actually escape? I guess if the crawl space walls have no vapor barrier, it can escape through that.
Lastly, I believe that a vapor barrier, unlike an air barrier, doesn't need to be perfect to be effective. I believe that have a 95% vapor barrier will give you 95% of the benefit. With an air barrier, any wind would drive the air infiltration through the remaining 5%, giving you less than 95% of the benefit. Hopefully someone else can verify that my recollection in this regard is correct. :-)
Cheers, Wayne
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wrote:

All these unknowns! I have an idea that'll make this part of the kitchen really unique. It'll be obscenely expensive. I'll redesign the floor so it consists of four hinged 6x6 hatches, with hardware as shown below, for lifting the hatches. If one insulation method doesn't work, I'll have easy access for trying another, and another...endlessly. Maybe I'll use teak.
http://www.jamestowndistributors.com/userportal/show_product.do?pid '31&familyName«I+Ring+Pull+Heavy+Duty+-+Lifting+Ring
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wrote:

I'm not real keen on removing blocks. The existing slots are in the 2-by wood which sits on the sill plate.
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Furthermore, I'm pretty sure most code requires a minimum distance between the ground and the house structure if it isn't concrete. Providing a medium that moisture can follow or that critters can burrow up into the house doesn't strike me as the best idea.
Given the limited area involved, boxing in the underside of the joists and then filling them with insulation might be a better alternative...
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There are alternatives to fiberglasss for batt insulation, like cotton or mineral wool.
Wayne
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Oh, why is that? Wayne
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Two reasons. First, houses tend to act as chimneys--warm moist air rises, finds a way out near the top, and thus floors tend to be under negative pressure--outside air is being pulled in down low. Even if this isn't the case, most floors are sheathed with plywood which which has a high enough perm rating to function as an air/vapor barrier. I have seen a number of floors which were covered on the cold side with poly and there were no apparent problems, though it would probably be prudent to use housewrap on the cold side just in case.
I meant to add to this discussion that most foams cannot be exposed in a crawlspace. they must be covered with a thermal barrier like drywall.
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That's true, but I think water vapor will still diffuse in all directions.

OK, so there's your vapor barrier on the warm side. :-)

Actually, I've wondered about that. Isn't the point of the thermal barrier to separate the foam from the living space? In that case the floor plywood would do the job and there wouldn't need to be a thermal barrier on the underneath.
Cheers, Wayne
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Actually, while there are definitely some gray areas in my mind concerning vapor barriers and floors, there is no gray area with foam in crawl spaces and rim joists (including the rim joist where the ceiling below is drywalled); the foam must be covered by a thermal barrier. At least according to how the code is interpreted where I live. I've spent some joyous time grovelling around in a crawl space screwing OSB onto ICF's per the BI instructions. There are some foams that meet the flame spread requirements, but not many AFAIK.
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Good to know, thanks. Wayne

One foam I was looking at said: ASTM E-84: FSI 15, SMK 450. That's presumably flame spread index 15, and a smoke criterion of 450. Do you know what the flame spread requirements are from the building code?
Cheers, Wayne
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That is why they are called out, to show they meet code. Check your local codes though, in case they differ.
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Or you can look for an ASTM E-84 fire rated surface foam, which can be exposed, but not to sunlight or a UV source. A crawlspace would have neither problem...
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Have you priced out the foam vs fiberglass? You'll need a mortgage for the foam. The latter will be pocket change.
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The spray foam I have seen applied is sprayed from a gun much like an airless paint sprayer sprays paint. You aim the gun at a surface from a fixed distance--about 12" is what I have seen--, be it a rim joist or wall sheathing or whatever, press the trigger, and it adheres to the surface and expands. I have never seen a foam application where you could pump it into a hole with any kind of predictable results.
If you could get in there enough to install some sort of sheet material (plywood, foamboard or the like) or even netting onto the underside of the floor joists, you could blow dense pack cellulose from the top through little holes in the subfloor.
The other alternative would be to figure out a way to insulate the stem walls, and then pump heat in there.
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closed cell foam is more expensive but unaffected by moisture, which is why its used. wet fiberglass or cellouse has near zero insulation value. plus foam fills all the little holes and voids. so it also stops drafts.....
makes for quiet warm area........
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I agree that closed cell foam is good stuff. But how do you propose he pump it through a little hole in the subfloor?
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theres a minimally expanding type that can go in walls floors etc.
i would probably excevate a trench access. eventually something else may come up requiring access under there. such access would help home resale
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