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billyh 03-23-2011 01:39 AM

Trying to update 60 year old basement/crawl... many issues & questions
I have searched for individual answers to these questions and think I have found a few but no definite answers for my specific situation. I know this is a long one but I sincerely appreciate any help in answering these questions (even if you can just answer one or two).

My house is built on Canadian Shield (rock) and on a slope. I have a crawl, about 6ft to bottom of joists on the downhill end which narrows to only a foot on the uphill end on one corner and about 4 ft on the other corner (land on one side of house is also higher than the other). After the house was built, they made an addition on the uphill side (a living room) by smashing through the crawl wall (literally). This area is about 2.5 ft high.

As for the finishing, there is nothing on the walls. There was white foam insulation (1"?) but I removed this to prep the walls for spray foam. Half of the original crawl has a solid base (either rock or concrete) and the other half is moist soil/sand. Under the living room is a combination of dry and moist fine sand. Where there is sand/soil there was a polyethylene barrier but it was thin and has since deteriorated.

For the questions:

I can remove some of the sand from near the walls in some areas. Would this be beneficial before I have the foam sprayed? There are areas where the inner sand level is level with the outside. What depth would be ideal to lower this to? Is it worth going through all of the effort to bring it down to the footings? (This would require removing 1 foot x 22 ft x 14 ft of sand for the living room area).

In the area where the crawl slopes up to within a foot of the joists, I had frost on the inside walls above the floor. I am assuming that this is because this area was not insulated well and the ground is so close to the floor. Is this correct?

In a few places, I can see that the wall ends and there is dirt/rocks underneath (sloping inward). Should I be pouring concrete up against this? Can I just spray foam over this? Should I do neither?

My crawl has my ducting, hot water tank and furnace in it, so I am assuming it is considered a conditioned space and should not be vented, but it has 3 vents in it (that haven't been touched in years). Any recommendations on how to proceed? If I close off the vents, what will happen to the moisture?

As in another post, my joists are set into the concrete. I read Gary's post here ( but I couldn't quite understand if spraying the entire concrete wall and header space with foam would be fine.

Since it is moist in the basement, and drywall is not a good idea to "fire rate" the spray foam, is my only other option a "shotcrete" style coating?

Thank you,

I live in Sudbury, ( so I am assuming it would be prudent to test for radon levels before sealing the floor of my crawl. Anyone run into high radon levels and had to solve it?

Edit: I don't have photos at the moment but I will provide some if needed.

algored2deth 03-24-2011 12:07 PM

Anything said here needs to be tempered with local bldg codes.

1) I would consider this condition spaced since you have h/w tank and furnace in the crawl. In that case, close off the vents permanently. 2" XPS rigid would be good. SF it in with the can stuff. Or caulk with silicone if you do a tight fit with the XPS to the opening.

2) If you have moisture issues, solve those first. If you had frost, that meant it was cold and there was moisture present as well. I would air seal all that you can (rim joist for example).

3) You will probably need a vapor barrier over the whole floor and ran up the walls 6". If you spray foam the walls, vapor barrier first than SF over the portion that runs up the wall. Vapor barrier will need mechanical fastening of some sort before SF.

4) As for covering the SF on the walls, you can use drywall which implies you have to build studded walls. You will have to use moisture resistant drywall, mesh tape, and sandable 90 type of wall compound. This is compound you have to mix yourself, not the standard premixed stuff. Putting regular paper based products in a moist area is a food source for mold. Or you might get away with intumescent paint. If you are having the SF done by a contractor, ask them for their take. Be aware, this paint is not cheap.

If you close off the vents, the moisture will remain unless you seal all air gaps and control the vapor coming through the ground. Once that is done, and if you still have high moisture, you may be stuck with getting a dehumidifier. You should get an idea of how much moisture you have now so that you can determine what the change is after you do your work. Sometimes you got to babystep it. Also, use a decent vapor barrier and not just some poly from the store. Your old one may have been destroyed due to nonideal soil content (ie it ate through the plastic). Vapor barrier sources: Tu Tuf, Drylok,, stego products, etc.

I would try and level out your whole crawl floor as much as possible. Get the SF to cover as much as possible. You will be scrubbing a lot of walls there because you need a fairly clean surface for the SF to stick to.

And I am sure that others will be along to provide appropriate links to the buildingscience website. Check those out as well.

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