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Old 02-06-2011, 11:15 PM   #1
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Question about crawlspace Vapor Barrier


I put a 6 mil vapor barrier down in my crawlspace. It is amazing the amount of moisture on the bottom of this barrier. I guess that means it is working.

My question is: what is the best way to attach the plastic to the cinder block foundation? Currently I just have some bricks holding it down to the ground every 10 ft. or so along the foundation. Is this enough, or should I literally try to seal it. What about the seams, should they be sealed, or is it enough to simply have each piece overlapping a few inches.

I had to install a sump pump in one corner of the space. It works well as this is the area where the water comes in so it gets pumped out from right where it comes in. I do, however, want to seal the vapor barrier to the foundation ABOVE the sump pump and pit as that are is pretty damp even though the water is getting pumped out. I'm hoping someone can tell me the proper way to seal the seams and "seal" around the edge of the plastic along the foundation walls. Thanks so much for your time. I am looking forward to not having to worry at all about what is going on in the crawl every time it rains hard. Thank again for any advice you have, I appreciate it.

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Old 02-07-2011, 08:37 PM   #2
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Question about crawlspace Vapor Barrier


I didnt have to deal with a sump pump but I sealed the plastic to the walls with caulk. I sealed the seams with caulk also, I overlapped the plastic by about two feet and made two lines of caulk to seal the plastic. I took the extra step of building a decking over-top of the plastic so everything is sealed.

Best of luck, I am interested to see what everyone else has to say.

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Old 02-07-2011, 09:12 PM   #3
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Originally Posted by JCAHILL4 View Post
I didnt have to deal with a sump pump but I sealed the plastic to the walls with caulk. I sealed the seams with caulk also, I overlapped the plastic by about two feet and made two lines of caulk to seal the plastic. I took the extra step of building a decking over-top of the plastic so everything is sealed.

Best of luck, I am interested to see what everyone else has to say.
Thanks for the reply. Is there a special kind of caulk for use on that type of plastic?
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Old 02-07-2011, 09:47 PM   #4
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Question about crawlspace Vapor Barrier


You can have a look at this link for just about all you need to know about this topic,

http://www.buildingscience.com/docum...ace-insulation

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Old 02-08-2011, 12:26 PM   #5
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Question about crawlspace Vapor Barrier


I am assuming that you live in an area with four distinct seasons. You don't say.

If you are looking for specific products to buy, try this but there are other means and methods to achieve the same thing:

http://crawlspaceinfo.com/catalog.html

I am not trying to promote them but I am doing the same thing you are and their site has been a part of my research. BTW, none of what I mention makes this an easy job as just laying bricks down. Their website also have some videos and readings as well.

The building science article looks pretty good. Be forewarned that if you insulate the walls, any kind of foam used will require a fire barrier like drywall. Check with local bldg code guys for sure but in general I think that is true. Think ahead how you would do that before you do so.

You will probably find contradictory stuff among numerous websites and opinions.

Simple answers: You will need to mechanically fasten the poly to the walls as well as with a sealant. On that website, they sell concrete fasteners and doublesided tape (FST foundation seal tape). You will need their waterproof seam tape as well for the poly. Let me point this out before somebody calls me out: You may not need to buy THEIR products but I am just saying it is one of many possibilities. Different tapes exist for different poly versions. Make sure you use the right one for the poly. Some may not stick as well as others.

At a bare minimum, acoustical sealant but mechanical fastening is best for long term durability. When you do the fasteners, you will need a hammer drill to go into the block.

You will need to overlap seams about 1ft or so and tape them. You want to make a very good seal/encapsulation here. You want this so that no moisture can get out. No air leaks at all (as best as possible).

Check out this link as well:

http://www.askthebuilder.com/445_New...etarders.shtml

as well as some other links on the askthebuilder site.


Before you do any of this, make sure your water problems really are mitigated.
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Old 02-08-2011, 01:44 PM   #6
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Thanks for y'alls time. I am in the Atlanta area. You have given me some good resources. I remember the guy from Ask the Builder talking about using a strip of treated wood (screwed into foundation) to secure poly. I will check out the link you sent and see if it is the same article. Thanks again everyone for helping me out with this.
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Old 02-08-2011, 10:17 PM   #7
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I just did this for my crawl space. I used products from crawlspaceinfo.com. I did not use the double sided tape but wish I did. It will give you the air tight seal you need. I used poly adhesive then poly tape. I installed foam boards on the foundation walls. Check with your local code if you don't have mechanical equipment in the crawl you may not have to install a fire barrier. The folks at crawlspaceinfo were helpful. Good luck.
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Old 02-10-2011, 01:08 PM   #8
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Question about crawlspace Vapor Barrier


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Originally Posted by Cleve99 View Post
Thanks for y'alls time. I am in the Atlanta area.
I'm about 2 hours north of you.

We had a guy with a certification come in and look at the crawlspace at work. Supposedly he is an expert and knows our area. He said just put the plastic down and overlap it. He said to cut it so it would run up the sides of the piers.

He said there was no reason to try to seal the various pieces together, that overlapping them (six to twelve inches) was enough.

When you're talking about concrete blocks, it's probably two different answers depending on if they're above grade or below. If they're above grade, and if you have a vented crawlspace, then don't worry about it. That's what we have here at work. He said just lap them up the sides a few inches.

I'm sure there's more than one way to approach this issue, but that's the advice we got (from a guy with a certification and malpractice insurance). YMMV.
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Old 02-13-2011, 06:26 AM   #9
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Question about crawlspace Vapor Barrier


Everyone has an opinion. Remember construction is mostly common sense. Your main goal is to stop the air transfer from the bottom of the crawl up into the house.

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