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mark2741 12-23-2011 10:18 PM

Crawl Space Questions
I'm in the process of finishing a section of my basement to turn it into a home office. This house was built in 1959 and about 10 or so years ago had an extension added to it. The extension is a family room and master bedroom. The family room on the lower level sits atop a vented crawl space. I say 'vented' because it has two small grate vents that are embedded in the block foundation of the crawl space.

In a corner of the basement that adjoins the crawl space (i.e., the original house basement) is a ~3 foot wide x 2 foot tall rectangular access cut out of the poured concrete foundation that leads to the addition's crawl space. Based on the metal frame that is in it, I'm guessing that it is just what was originally a well window frame where they took the original window out once the addition/crawl space was put in.

My questions:

a. Since the crawl space has the two small vents, one on each side of it, in the winter it lets in a lot of cold air and makes the basement cold. Since I'm now finishing a portion of the basement (it will be insulated), I'd like to cover up the access to the crawl space to block the cold air from coming into the basement.

b. Currently, the crawl space is uninsulated. The family room that sits above it is always colder than the rest of the house in the winter. There are two ducts running heat/AC from the basement to through the crawl space to vents feeding the family room, but with a constant, unfettered stream of cold air coming into the crawl space via the vents it makes for a very cold crawl space in the winter and thus a cold floor (doesn't help that the floor is laminate wood!). I did some reading and it sounds like the way to help with this would be to put bat insulation on the floor joists in the crawl space, with the paper side 'up' against the underside of the floor, and also to lay down 6 mil plastic along the entire floor of the crawl space. While I'm a bit claustrophobic and don't look forward to crawling around (the crawl space has about 3 feet of 'headroom'), this sounds doable over a weekend. Does the plan make sense?

I could snap pics if it would help.

Gary in WA 12-23-2011 11:20 PM

I would insulate the duct work after taping or mastic on the joints to more than minimum (Code) requirements for your area. Build an insulated/weatherstriped door between spaces. Foamboard and air seal the rim joists in both addition/basement. Insulate the floor if going with vented: Amount and type depends on location. Lay plastic on dirt first:


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