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Split basement needs vapor barrier

Keeping ground moisture at bay
Published on Nov 6, 2007

Q: My 1920s home has part basement and part crawlspace underneath it, with a partial wall that separates the two sections. Is it a good idea to cover the dirt portion with plastic? Should I extend the wall all the way up so the two sections are separated? --Dan A. A: It's fine to lay plastic over the dirt portion of the basement -- in fact, it's required by most building codes. The plastic acts as a vapor barrier to prevent ground moisture from getting up onto the wood members and insulation. The recommended material is 6-mil black plastic, which you can get at any home center or lumber yard. The only reason to raise the wall between the basement and the crawlspace areas would be if you want to turn the basement area into living space. In that case, the crawlspace areas need to be blocked off from the basement, insulated, lined with a vapor barrier, and have cross ventilation to the outside. If all of the basement and crawl areas are nonliving space, then you can leave the partial wall...

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