Published on January 31st, 2013 | by Henri


Insulating a basement when remodeling

Q.    I am remodeling my basement. I live in the northern part of Illinois where temperatures get fairly cold in the winter (approximately 30 F. to minus 10 F.).

I am replacing the paneling on the walls with wallboard. The 2-inch by 4-inch wall structure is in place with a 6mil plastic sheeting between the wall studs and the concrete foundation. I never get any water in the basement.
My questions are:

1. Should I leave the plastic sheeting in place and put batt insulation with paper backing facing the inside of the basement?

2. Should I put the batting all the way to the floor or leave a couple of feet for the warm air to penetrate to the outside to prevent freezing along the wall?

A.    In answer to your questions:

1. Cut off the plastic at the grade line and hold it in place with a few tabs of duct tape. You only want the plastic to prevent any leakage from wetting the insulation but there should be some exhaust for any condensation, however minor it may be, to dissipate instead of remaining trapped against the foundation walls where mold could develop.

Use unfaced insulation and staple 6-mil plastic to the studs to provide the best vapor retarder possible. Any moisture in the room will easily bypass the Kraft paper, migrate through the insulation and find a plastic film in contact with a cool foundation wall. Condensation is likely to occur on the room side of the remaining plastic, where it will be trapped and wet the insulation.

2. Unless you know that there is a functioning footing drain and that the foundation was backfilled with stones and coarse material, and you make sure that the grade against the foundation is sloping away for good drainage, you should not insulate any lower than three feet below the outside grade level. This is to allow some heat loss through the foundation to keep frost at bay so it won’t crack your walls.

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