# Basement insulation on pre-built walls



## hyunelan2 (Aug 14, 2007)

From what I can recall, your plastic vapor barrier is on the wrong side of the wall - it should be on the "warm" side. The water that rots your studs is not from the wall, it's from the moist air. As the warmer moist air encounters the cold air, condensation occurs. The point of the plastic vapor barrier being on the inside of the insulated wall, is to keep the moist air from being able to enter the stud cavities. 

IIRC, it's also not a good idea to put plastic on both sides of the wall, as any moisture that does get in, will be trapped.

Wait for someone who has better knowledge of the older insulating (Pre-EPS) methods to come give you some advice.


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## brockmiera (Oct 9, 2012)

Pull the plastic and spray foam.


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## spring3100 (May 6, 2011)

Vapor barrier should be on the warm side,if at all.

If you can't afford spray foam,and XPS between cavities won't give you a vapor barrier,I would recommend using ROXUL between studs,it will give you R-15 versus R-13 for batt insulation,doesn't itch,cuts very easily for a perfect fit.

Its available at Lowes,and a few Home Dpot.

As regards a Vapor barrier on top of that,you will get 800 different opinions on whether to do it or not.

Remember,if you're going ultra cheap and use fiberglass,use unfaced batts,as paper on regular insulation will promote mold growth.


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## davinciwanab (Feb 26, 2013)

*Thanks!*

@spring3100 - I've not heard of that Roxul, but that seems to be the way to go! Even with my ~1700 sqft basement, it looks like Roxul will only cost around $400 - certainly more expensive than fiberglass, but - seems worth it.

Also, on their website, it suggests building the walls, putting in the insulation, then adding the vapor barrier on top of that (similar to what everyone online including hyunelan2 and yourself say)

Thanks!!


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## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/documents/published-articles/pa-built-wrong-from-start

http://www.buildingscience.com/docu...merica-high-r-foundations-case-study-analysis

http://www.buildingfoundation.umn.edu/OCBasementSystem/ProjectReview.htm

Gary


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