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Plastic vapor barier for ground crawl space

Cynthia Jones's Avatar

Join Date: Apr 2006
Posts: 22

04-21-06, 08:59 AM   #1  
Plastic vapor barier for ground crawl space

I have a 1939 brick bunglow that I want to put a plasic vapor barier on the ground crawl space. What do I tack it down with?

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majakdragon's Avatar

Join Date: Jul 2003
Posts: 7,827

04-21-06, 11:00 AM   #2  
You do not need to tack it down. Use at least a 6 Mil plastic and overlap each piece by one foot. You can tape the overlapped pieces if you wish. Ideally, it should also go up the walls one foot and can be taped at the top to hold it there. Good luck.

Concretemasonry's Avatar

Join Date: Mar 2005
Posts: 6,125

04-21-06, 01:08 PM   #3  
Plastic vapor barier for ground crawl

You may want to consider something thicker considering the minimal extra cost and the durability in a ground application.

A 6 mil poly is techically an adequate vapor barrier for walls, but something like 10 mil is better. Your vapor barrier may be subjected to being crawled on, abrasion and other hazards during the life on the ground.

Just a thought since you only want to do it once.


twelvepole's Avatar

Join Date: Aug 2000
Posts: 15,834

04-21-06, 01:26 PM   #4  
Thicker the better. The National Oak Flooring Manufacturer's Association recommends 8 mil minimum if installing hardwood over crawlspace.

XSleeper's Avatar
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Join Date: Dec 2004
Posts: 19,343

04-21-06, 05:48 PM   #5  
If the poly needs to be secured for some reason- such as to keep it from moving as you install it, or if it's frequently crawled on- you can use 6" galvanized spikes and oversized washers. Duct tape and mastic brushed over the patch will help ensure the poly does not tear at those fasteners.

You could also consider laying some carpet remnant runners in areas of the crawlspace that are frequently travelled, to avoid ripping the poly in the future. Rather than just covering the floor, running the poly up the foundation walls is recommended. Mastic serves as the glue to hold the poly in place on the foundation walls, and can also be used to cover any taped seams. Just do not nail the poly to the wood sill plate, for fear of causing moisture damage or impeding future termite inspectors.

The best article I've even seen on sealing crawlspaces was in the 10/2003 Journal of Light Construction.

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