c. Vapor barrier needed/Incomplete:
Crawl spaces or basements that have dirt floors should have a vapor barrier (Fig. c1, Item A) laid over the dirt to prevent the rise of moisture from the earth (Fig. c1, Item B). It is surprising how much moisture can rise from the earth, especially from what appears to be relatively dry earth. Many crawl spaces will have old roofing fells laid over the dirt to act as a vapor barrier. These often deteriorate and become worthless within 10 years. Other crawl spaces will have only a minor section covered with a vapor barrier. Vapor barriers should extend over 100% of the earth, and cover the lower portion of the foundation wall as well.
WARNING: Vapor barriers in direct contact with wood members can cause those wood members to get wet and rot out. This is why vapor barriers are usually kept back about 2 inches from wooden posts, etc.
What to: How to:
A good and relatively inexpensive vapor barrier is polyethylene plastic sheet in 6 mil or greater thickness. This material comes in 12 foot widths (folded four times, rolled and packed in boxes 3 feet long that covers 500 to 1,000 sq. ft. for around $30.00). The black material won’t deteriorate in sunlight. Clear plastic will.
Simply spread the plastic over the dirt. Make sure any wood or trash is removed first. Once the plastic is on the floor, people are more likely to enter a crawl space since they won’t get so dirty. This tends to increase the acceptability of entering the space to perform maintenance inspections. |
