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davinciwanab 02-26-2013 04:15 PM

Basement insulation on pre-built walls
My question - I understand I'm not in the ideal scenario, but - what would be the best way to go from here?


My basement walls are already built (2x4 walls about 1/8th inch from the poured concrete - some areas are touching). Behind the 2x4 wall is 6mil plastic from floor to ceiling. Bottom 2x4 is treated lumber.

I realize this is not ideal, and have read a lot of things about how it would be much better to have the large EPS sheets THEN the wall, but - I really don't want to tear down all the walls to put that up behind.

I have not had any water problems, dampness...etc at all in my basement. I've done the plastic test on a few 3'x3' areas during very rainy days, and saw no moisture build-up (but have read that condensation can happen once you start insulating).

My current thoughts/questions/options:
  • do I pull the plastic or leave it? Or pull it and put plastic up over after the insulation? If I leave it, do I need to go around and make sure it's sealed better? (currently duct-taped together in overlapping spots)
  • do I use normal insulation, or buy 14.5" sheets of EPS to put between the studs? If I use EPS, so I need some kind of caulk between it and the studs?
  • if "normal" insulation, should have it have a paper face or no?
  • it seems like sheets of EPS put in-between the studs would help from an anti-mold perpsective, but... would that insulate well? Also cost a lot more I assume, but...

ANY suggestions/helpful hints/thoughts are welcome... there are MANY resources for "how to finish a basement", but very few (none) that would help on where to go once you've already started down the wrong path.

The goal is to finish the basement completely with nice rooms...etc as if it were a normal living area in the house.

My house is in Ohio - it gets very warm, very cold, and and wet - just about everything.

Thanks VERY VERY much for any help!

hyunelan2 02-26-2013 04:25 PM

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.

brockmiera 02-26-2013 05:13 PM

Pull the plastic and spray foam.

spring3100 02-26-2013 08:27 PM

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.

davinciwanab 02-27-2013 02:42 PM

@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)


Gary in WA 02-28-2013 07:10 PM



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