Vapor Barrier


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Old 06-05-14, 01:41 PM
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Vapor Barrier

I am looking to replace the current vapor barrier in my crawl space.
I have a few questions after searching how to install vapor barriers.

What is the difference between a clear and black vapor barrier?
when installing the vapor barrier it seems my searches recommend installing the vapor barrier up half way of the foundation. Wouldn't this keep or send the moisture up to the foundation wall? this would be a bad thing correct?

When laying the barrier down do i need to over lap each piece and by how many inches or feet? Does this need to be taped or just landscaping clips?

Thanks.
 
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Old 06-05-14, 02:04 PM
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Clear or black, are both black in the dark. Black is preferred if you have venting as clear will allow for vegetation to grow beneath it if light enters the vents, so I'd go with 6 mil black. Over lap it at least two feet and tape the joint. I like to use Tyvek tape, as it holds great. Do you have foundation vents? Probably not in Idaho, but had to ask.
 
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Old 06-05-14, 03:07 PM
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I do have vents.

What about installing the vapor barrier up half way of the foundation. Wouldn't this keep or send the moisture up to the foundation wall?
 
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Old 06-05-14, 04:04 PM
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It is best to run the plastic all the way to the rim joist, but you have vents. There are two schools of thought that are argued here. Seal up the crawlspace and air condition it. Or run the plastic to the bottom of the vents, attaching it to the concrete with A/C duct mastic and let the vents do their job. Hang in there as both sides will be addressed, I am sure. You will need to choose. Running the plastic up the concrete won't vent moisture up to the joists.
 
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Old 06-05-14, 05:13 PM
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Black poly, as Chandler states, is better at preventing vegetation.

You didn't mention what the foundation material is or what your soil conditions and water conditions are. Moisture wants to go from high concentration to drier air. Under most circumstances moisture will never ventilate to the ground that is adjacent to your foundation. It will migrate up the wall and ventilate to the air as it approaches grade. Under severe enough conditions of high moisture and cold winter temperatures you can expect to see spalling of the concrete or block at the point of a few inches above grade.

If your foundation has a good waterproofing/vapor proofing membrane on the exterior below grade, this will reduce the moisture load to the wall and help to eliminate or minimize spalling. If there is a water/vapor barrier under the footings then you are gold. Doubtful that you have these extra nice barriers so you have to make the call as to whether or not running poly up the walls is a good move. If you see evidence of spalling or severe efflorescence on the exterior at the point of grade then I would probably opt not to run the barrier up the walls.
 
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Old 06-09-14, 09:59 AM
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Old 06-09-14, 01:39 PM
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Yep. Not pretty, not cheap, but it will stick and stay stuck.
 
 

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