Vapor Barrier over basement wall or not??

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Old 09-28-18, 04:23 AM
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Vapor Barrier over basement wall or not??

I'm going to be doing some work on my basement next week. This basement will never be finished. but I'm just trying to keep it dry. The floor is currently crushed stone. I may decide to put concrete over it some day, but have not made that decision yet.

I've already finished up exterior work; gutters, etc.

I'm planning rigid foam insulation on the walls.

I am doing a vapor barrier over the floor.

My question is regarding a vapor barrier over the walls.

There is a lot of info out there on the web about not putting any type of vapor barrier over the basement walls at all. But one of the manufacturers of vapor barrier suggests putting their barrier over the wall.

Check out this link

http://crawlspaceinsulation.com/properly-installing-crawl-space-insulation/

So do I put the barrier over the wall or not?? Or floor only?
 
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Old 09-28-18, 07:21 AM
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If the goal is to keep the basement "dry", then does that mean you have a moisture problem? If so, a waterproof coating or membrane on the exterior of the basement wall all the way to the footing is the best method IMO. If you're talking about humidity, then good air circulation, sealing all cracks/crevices and some foam board glued directly to the foundation wall would be called for, if I am not mistaken. Basically, you want to keep outside moisture out while at the same time preventing warm humid inside air from contacting cold surfaces (concrete walls and floor), while providing good circulation to keep air moving.

It is my understanding that if you have exterior moisture infiltration, installing a vapor barrier would trap the moisture behind the barrier and mold would grow. In this case, you wouldn't want a barrier and would want to allow the moisture to dry to the inside. However, fixing the moisture infiltration problem would be the best route, although it's expensive to excavate around the entire home and have a barrier installed.

Is the basement a conditioned space?
 
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Old 09-28-18, 07:29 AM
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True, the exterior solution is not going to happen though due to all the digging, etc, that would need to be done.

Much of the new building science information that you see on the web today discourages the use of any vapor barriers on the wall in the basement/crawl space.

But, it seems like the manufacturer of a product that I am looking at suggests otherwise and shows the vapor barrier going over the insulation which goes over the wall (the link I provided). Most of time time, recommendations are given to follow manufacture instructions.

Therefore there are 2 conflicting theories here. Thus my question.
 
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Old 09-28-18, 07:44 AM
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The link doesn't open for me... and anyway the name of that page is "crawl space" insulation... not basement insulation. Current thinking on crawlspaces is to completely encapsulate and then condition them. You are asking about basement walls, which should not have an interior vapor barrier.
 
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Old 09-28-18, 09:21 AM
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How do you decide if it's a crawl space or a basement?
 
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Old 09-28-18, 09:47 AM
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When you go in your basement are you on your knees? That's a crawl space. In a crawl space, the majority of the foundation wall is above grade, not below grade. You can stand up in a basement, dirt floor or not. Basement walls (below grade) are as cold as the ground is and the wall needs to dry to the warm side if it happens to be moist.
 
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Old 09-28-18, 10:18 AM
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My ceiling height is about 5 1/2 feet so I'm not on my knees, but I am hitting my head.

I guess, does it matter whether it's called a CS or a basement?

Building science is saying a crawl space should be treated the same anyway (they call it a mini basement)

Link
 
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Old 09-28-18, 11:06 AM
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Well, basement denotes that it's below grade. Crawl spaces are often on or near grade. But there is sure to be some in-between somewhere along the way. How it's treated may depend somewhat on your climate and we have no idea where you live because you haven't filled out your profile. Quebec might be treated different than Mississippi. But building science is a good source for accurate information.
 
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Old 09-28-18, 11:20 AM
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North Eastern Pennsylvania
 
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