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I have been helping my aunt excavate her back yard, in order to expose
hot water pipes, that run about 30 feet from the house to the garage.
Both the hot water heater and the natural gas boiler are in the garage.
The pipes are not insulated and are just about 18 inches below grade,
in Cambridge, Maryland (8 feet above sea level). Last year's heating
bills were astronomical, and my Aunt thinks that a lot of heat was
radiated into the frozen ground, before it ever reached her house.

My question is, once I expose the pipes completely, what is a good
method of insulating pipes in sandy and wet soil. Cutting the pipes are
not an option, thus we need something to retrofit. The insulation must
withstand backfilling, vast temperature changes, and moisture. What can
be used on this job?

Note: The house was built in the 1940's. In addition to fixing the
pipes, my Aunt is also insulating the house's ceilings and walls.


Will the ground on top be subject to heavy loads like parked cars or an
occasional delivery truck or is it strictly foot traffic or garden area.

For the lighter loads I might try expanding foam mixed from a 2 part mix and
poured right on the pipes with minimal form around it to control the
expansion. May even be insulation contractors who can dispense the stuff
from a truck.

Simple closed foam (cell pipe) insulation would be better than nothing but
may compress a bit. Maybe two concentric layers.

Here is an idea: Take a piece of 4" PVC pipe and use a router to cut a slit
along it wide enough to get the hot water pipe into. Fill the pipe with
expanding foam insulation (or whatever you want) and seal the slit with
mastic or aluminum duct tape and bury slit side down.




I think you might also be able to cut a long section of 4" PVC pipe (along
the long axis or maybe just a slit wide en