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Vapor Barrier- in Crawl Space Insulation

guzda's Avatar

Join Date: Aug 2001
Posts: 19

10-06-03, 07:31 PM   #1  
Vapor Barrier- in Crawl Space Insulation

Argument ensued over vapor barrier placement in floor joists over crawl space. No vapor barrier over bare earth. Insulation placed between joists with paper facing down-(ie) away from floor with paper flanges stapled to bottom of joists. Contractors said it's always done this way. I say paper goes next to floor- toward the heated side. Please advise proper method.
Ol' Guz

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resercon's Avatar

Join Date: Nov 2001
Posts: 1,873

10-06-03, 08:57 PM   #2  

This is a Dept.of Energy brief on vapor barriers. It clearly states that the vapor barrier in your area should face the warm side of the house, which means when installed in a crawlspace, the paper faces the subfloor. This also means you cannot staple the vapor barrier to the floor joists.

The ground cover for your dirt floor in this crawl space is known as a moisture barrier. The difference between a moisture barrier and a vapor barrier is vapor barriers deal with diffusion and moisture barriers deal primarily with capilliary action. In other words, moisture barriers do not have to be vapor barrier rated.

Ed Imeduc's Avatar

Join Date: Aug 2002
Posts: 18,389

10-08-03, 11:08 AM   #3  
crawl way

Like resercon said. That builder you have sure has it wrong. You want a good 6 mil poly down on the ground over lap 2' and tape the seams. go up the wall 2' with it. Put a 2" polystyrene on the walls up to the joist. In the joist space there on the sill plate put cut blocks of R 19 all around the home. If you have the duct work down there we put small outlets in it ED

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