The water pipes in my crawl space freeze every winter. Are there any really effective steps I can take to keep this from happening?
Solving Water Pipes Freezing Problems
Most houses with crawl spaces are located in the Southeast and Far West, regions with lower than average heating requirements and somewhat higher humidity levels. With a few exceptions, less than 20 percent of the houses in the rest of the country use such perimeter foundations. Because a crawl space is somewhat exposed to the environment, even brief cold spells can freeze water in the plumbing beneath the house with pipes freezing.
The simplest solutions — allowing the faucets to trickle constantly, or wrapping the pipe runs with electrical-resistance heat tape — are also the most wasteful and not always 100 percent effective for pipes freezing. A better remedy would be to insulate the plumbing with foam wrap made for this purpose, and close the perimeter vents during the coldest months. In higher-humidity areas, however, this might encourage floor-joist and structural decay, especially if the wood moisture content exceeds 28 percent.
Since water tends to freeze at the points of maximum restriction, a low-wattage light bulb placed near a chronic tight spot (an elbow or reducer, for example) might solve the problem. Also, if you're replumbing, consider routing the runs alongside heating ducts where possible—and keep in mind that plastic pipe is a better insulator than conductive copper.
Probably the best permanent fix is to apply extruded polystyrene insulation board to the perimeter wall with construction adhesive. (If it's placed outside, protect it with a parge coat or some other material.) It should set you back about half the cost of floor insulation and will protect both the crawl space and the living space above it. If under-house moisture is a concern, consider laying sheets of 6-mil polyethylene over the earth in the crawl space and holding the plastic down at the edges with bricks or cap blocks.
— Dennis Burkholder, research staffer