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Old 05-14-2012, 10:51 PM   #1
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Vapor Barrier Help


Hi,
My house has a partial basement (concrete floor) with a crawlspace (dirt floor) on either side. I had spray foam installed in each crawlspace on the walls, but the company did not install a vapor barrier on the dirt floor of the crawlspaces. I am going to be installing a vapor barrier, and am trying to figure out best way to attach the vapor barrier to the existing spray foam. Has anyone dealt with this before? Would it best to tape it or would I need to mechanically fasten it someway? The spray foam is a around a 2-3 inches thick. Thanks for your help!

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Old 05-15-2012, 12:14 AM   #2
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Vapor Barrier Help


The v.b. should have been installed before the SPF, fig.#11: http://www.buildingscience.com/docum...ance-and-codes

Where are you located? In a radon area?: http://energy.cr.usgs.gov/radon/rnus.html

Termite area?: http://termites101.org/termite-basic...ites-by-region

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Old 05-15-2012, 07:42 AM   #3
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Gary,
Thanks for the reply. I am not in a radon area, and termites are not a huge issue. I live southeast of the Adirondacks in New York. I realize now that this was not done correctly, which is why I am trying to do what I can to fix it.

I do not have an issue with water draining into my basement or either crawlspace; however, since the spray foam has been installed it has gotten much more humid than before in the basement. The foundation is field stone, and the house is about 110 years old. I am not sure why the company I hired to do the work did not put in the vapor barrier; however, I need to put something down. I have a dehumidifier hooked up to a condensate pump that I just started using, but this isn't going to cut it as a long term solution.

Will it be OK to attach the polyethylene VB to the spray foam and overlap? I know this isn't ideal, but wouldn't be be better than the open dirt floor? Additionally, should I use a spray glue safe for spray foam, or would tape suffice? Mechanical fasteners seem like it may help, but again, I am at a loss. I just need to fix this humidity problem.

Thanks.
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Old 05-15-2012, 08:13 AM   #4
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Ideally it is best to attach directly to the wall.

Is the spray foam they applied open or closed cell?

If it is closed cell, you can attach the vapor barrier to the foam and spray foam it tight if need be.
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Old 05-15-2012, 10:00 AM   #5
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I realize that it should be attached to the wall; I am not debating that. Unfortunately, I can do nothing about it other than try to find a solution that cuts down on the moisture. However, I do appreciate everyone's input.

My only alternative would be to rip out all of the spray foam and start from scratch. I do not really want to go that route, or can I afford to financially.

It is closed cell spray foam, and is fairly uneven at all points. Would I use an open cell to attach/seal up the vapor barrier once attached? Would I staple and then tape it with appropriate tape first? Will the solvent on the tape dissolve the existing spray foam?

I just need to find a way to attach the polyethylene sheeting to the uneven, existing spray foam. The humidity is an issue and is going to have an adverse effect on the air quality if it is not addressed.

Any other thoughts on what I can do? Thanks.
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Old 05-15-2012, 10:56 AM   #6
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I know that you know it was supposed to be attached to the wall.

I was just answering the first question.

Given that the foam is closed cell, at 2-3 inches it is pretty vapor impermeable. That being the case, attaching to the the foam if fine.

You could run your vapor barrier right up the foam (10-12 inches up the wall) staple it to the foam, cut the vapor barrier at a uniform height around the foam surround.

Once that is done, you can seal it to the foam however is easiest for you. As small froth pack or 2-part kit of foam would probably yield enough foam to spray that connection/intersection of the vapor barrier to the foam.

If you are a bit more patient, you could seal the plastic to the foam with acoustical sealant or other compatible sealant.
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Old 05-15-2012, 11:18 AM   #7
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Windows on Wash, you are the man! Thanks for the help. Do you think it would be worth while to tape the seams before applying the spray foam?
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Old 05-15-2012, 01:19 PM   #8
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At the spray foam connection (i.e. crawl walls)?

If that is what you were meaning, not really. Just hit it with what sealant/foam you are going to use.
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Old 05-15-2012, 03:07 PM   #9
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Toward the end of the first link I gave you, it discusses code on the taping or sealing all the 6" overlaps of the plastic.

Did the company install an interior drainage system to reduce the high humidity (previously through the stone wall), now under and behind the wall/foam, pooling at the base of the stones where it could freeze and lift the wall? http://www.buildingscience.com/docum...ance-and-codes

Figure #2: http://www.buildingscience.com/docum...le-foundations

Did they install an ignition barrier or coating on the SPF as per Code? Is the basement separate from the crawl spaces with air-tight doors? Will there be air changes as per Code in the crawls as the first link said? eg; http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf

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Old 05-15-2012, 03:56 PM   #10
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+1

Definitely need an ignition barrier overtop of everything when done.

Interestingly enough, they don't care about sheet plastic but they do care about foam. Go figure.

Did the poster mention issues of water infiltration through the field stone wall previously? I may have missed that part.

If water wasn't and issue previously, it certainly shouldn't be now.

I would theorize that the added humidity is from the inability to vent to outside now and all that trapped moisture in the air.

Take some rH measurements both before and after installation of the vapor barrier on the floor.
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Old 05-15-2012, 04:03 PM   #11
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Gary,

All the company did was install spray foam on the walls for the crawlspace, and some blow in insulation in the attic. Nothing else. They were supposed to install a vapor barrier before the spray foam, but that is another issue. The crawlspace is not vented. It is just as it was when it was built 100 years ago, with the exception of new electrical lines, plumbing, and some jacks. No ignition or barrier coating was installed, and there are no doors segregating the crawlspaces from the basement.
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Old 05-15-2012, 04:08 PM   #12
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Windows on Wash,
I will have to look into the ignition barrier. I just reached out the company; they are going to be taking care of this unless they can produce documentation about the product they used indicating otherwise. There was no water infiltration previously; it was fairly dry. It is not "wet" in the basement; the humidity has increased since the spray foam, and I have also wondered if it was due to the inability for the moisture to vent outside. I have a couple indoor air quality meters for work that I have used, in addition to the notoriously inaccurate RH sensor on my dehumidifier, and levels range in the 70-80 % range in the summer. I am not sure what it was before, but it was not bad at all in the basement before the crawlspace as far as any olfactive indicators of mold or general air quality issues are concerned.

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