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.