Q. I currently work in a mountain region where the winter temperatures go well below freezing. Water lines are set 4 feet below grade. In this climate, how would you recommend bringing a water line through a crawlspace and into a house? Code here requires a ventilated crawlspace.

A.Felix Marti responds: We have had to deal with this exact situation. We work in a mountain region with elevations between 8,000 to 10,000 feet, and frost depths from 4 to 5 feet. We detail the pipe as follows, and so far we have not been called back to repair a burst waterline.

While the trench is open and the water line is being plumbed into the house, we insulate the pipe all the way to the bottom of the trench. There are several pipe insulations available. We typically use Rubatex — a rubber-based, closed-cell foam insulation (Rubatex, 906 Adams, Bedford, VA 24523; 800/782-2839), or Owens-Corning SSL-2 fiberglass pipe insulation (Owens-Corning Fiberglas, Toledo, OH 43604; 419/248-8000). Then we slip PVC pipe over the insulated pipe, making sure that we leave at least on inch of air space between the pipe wall and the insulation. We extend this pipe from the subfloor down to the bottom of the trench, which is below frost depth.

The plastic conduit allows warm, below-grade air to rise, warming the insulated pipe in the crawlspace. In one case where we wanted added insurance, we installed a PVC elbow at the bottom of the stack and extended the plastic conduit back about 30 feet along the trench. Then, before backfilling, we laid 1-inch rigid foam on top of the PVC. In theory, the added length of conduit enhances the convection of ground-temperature air in the PVC stack.

For additional peace of mind, it would be a good idea to wrap the outside wall of the PVC sleeve within the crawlspace to keep the rising air from cooling the air in the pipe. However, we have not done this, and have not had any problems.

Felix Marti is a builder and remodeler in Ridgway, Colo.