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.