Sealing crawlspaces and insulating them with polyurethane foam

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Permalink Reply by Evan Mills on April 6, 2011 at 1:22pm

Interesting .... And what does that cost?  I just got a $7000 estimate for doing 2" of sprayfoam under my floor..... ouch.   Maybe 3x the savings of fiber (??), but also 3x the cost.....

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Permalink Reply by Dianna Winsett on April 8, 2011 at 8:32pm

Dec 2010, I had the underside of a 2000 sq ft older manufactured home, sprayed with open cell foam. Ripping out the sagging insulation and belly paper, spraying at least 3 1/2" of foam directly on the underside of the floor and totally covering the duct work (which hung below the 2 x 6 floor joists) cost me $3250. We are in the DFW,TX area. I am mostly pleased. I had expected the cavities to be filled, but they told me over 3 1/2" would not be more effective.  Hmmm.  I do feel a tightness, but with elec air, and propane heat, it is hard to gauge true savings. They were to come back out and inspect the work, but phone tag has been  exhausting.

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Permalink Reply by David Meiland on April 6, 2011 at 9:11pm

George, one product for crawlspace VB is Dura-Skrim. I am very skeptical of spraying foam directly onto dirt, but like you say, maybe that didn't happen.

 

Evan, are you sure foam would give you 3 times the savings of fiber in an under-floor installation? That seems high to me. If you have a very leaky floor (like mine--old t&g fir over diagonal planks with no paper between) then maybe it's the right approach.

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Permalink Reply by Mike Estupinian on April 8, 2011 at 9:58am

George, I saw that episode as well.  The floor was a slab they had discovered had no vapor barrirer.  They had discovered that by breaking up part of the slab for a draining issue.  They repaired the drain then decided to use the foam to act as a barrier before they put the flooring down.  I really would like to find out if it worked, sounds like it would!

Mike

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Permalink Reply by George M. Matthews on April 8, 2011 at 1:55pm

The Holmes crew is busy. I watched a different episode. They opened up a "raised" kitchen floor, found no crawlspace beneath and decided to dig it out maybe 24 inches deep so they'd have access. That is where I must have gotten a snack... the next thing I saw was spraying PU foam and installation of an anti-ignition barrier on the foundation walls and then they poured a thin layer of self leveling concrete on top of the foam.

 

The Q is, what steps did I miss? As we know from TV, Mr. Holmes does everything "by the book".

 

I probably ought to buy one of Joe Lstburek's books to get it right. Unless he or Mr. Tooley are on this forum.

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Permalink Reply by Dale Walker on April 9, 2011 at 1:57am

My brother and I built a 750 SF cabin over a crawl space on the Brazos River in North Texas and am having moisture control problems in the crawl space.  We've laid out 6 mil plastic and overlapped and we need to seal the laps and mastic to the sides of the foundation.  We think we need to spray foam the rim joists to seal them as well as insulate against the outside.  However, the rim joists are sweating pretty bad inside the crawl space right now and I'm not sure how to dry this thing out so the foam will stick.  Any thoughts?

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Permalink Reply by David Meiland on April 9, 2011 at 7:33am

Dale, get your ground cover installed and sealed everywhere, and make sure surface water and downspouts are directed well away from the building.

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Permalink Reply by Dianna Winsett on April 9, 2011 at 1:57pm

Are you sure the moisture is "sweating' on the rim joists.  Condensation between hot and cold. Or, could it be condensation in your walls dripping down to wet the rim joists?

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Permalink Reply by Glen Gallo on April 12, 2011 at 7:11am

I saw the same episode. One concern I have is that I saw no drainage or stem wall remediation. It is possible I missed it. I think a wall must be able to dry somewhere otherwise the result will be a concrete wall unseen with dirt one one side and sealed behind foam on the other wetter than a sponge on the ocean floor.

 

Now this might be more or a regional issue on my part but most stem walls I see are buried often for most of the perimeter. We have mostly slab on grade but there are old Craftsman homes in many areas. The method most often used was dig a hole install a stem wall and back fill.

 

For this type of situation I believe sealing the stem wall unwise. My thought is a good vapor barrier and possibly a dehumidifier with a pump out. My climate is very dry for the most part (San Diego CA)

 

I welcome any input.

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Permalink Reply by Dale Walker on April 13, 2011 at 2:24am

The water is beading up on the rim joists on the inside.  I don't believe I have condensation in the walls but I don't know for sure.  The wall construction is 2x4s, R-13 batt insulation with OSB sheathing on the outside, a tar paper water control layer and then a 3/8" smart siding.  I did a blower door test on the cabin after I caulked every hole I could find and the air changes was .14 so it is pretty tight I think.  The guy told me if I slammed the front door, it would flush the toilet.

 

I am thinking I need to set a dehumidifier down there termporarily so I can dry it out enough to insulate the rim joists and seal the 6 mil plastic everywhere.  Except for the tar paper, it is solid wood from the inside to the outside at the rim joists so I am thinking I have some thermal bridging issues at the rim joists and the temperature differential when it is cold outside is causing the sweating on the inside.  I am about 500' from the river as well and the soil is sandy so I suspect I just happen to be in a location where I have quite a bit of moisture rising from below.

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Permalink Reply by John Tooley on April 23, 2011 at 2:23am

Dale, the rim joist my have condensation due all other wood in the crawl is now drying to the cold rim. Run a dehumidifer for a month and then insulate the rim.

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Permalink Reply by George M. Matthews on May 2, 2011 at 9:59am

My client has a 2300 sf single story house with a perimeter concrete foundation on expansive clay soil. Beyond saving 15% on energy costs will a thick sheet of plastic on the entire crawlspace (sealed) keep the soil moisture content stable enough to stop the annual movement of the soil in the California Mediterranean climate where it may not rain from May to late November?

It would be nice to have an additional selling point to a system that may cost around $7000

Thanks for any help you all can give on the subject..

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