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protecting exposed underground water supply main

dpare | Posted in General Questions on

In excavating under the front porch of my house for a basement walkout, my mason exposed the house’s water main which had previously been buried below the frost line (approx. 4 ft).   A footing and 8 in block retaining wall was built in such a way where  about 5 ft. of 1 in copper pipe is now exposed to the outside  air.  The pipe sits about 3 inches from the floor and 3 inches from the retaining wall in the bottom corner of  the excavated outside walkout area. My obvious concern is how to prevent this pipe from freezing in the cold New Jersey winters short of abandoning it and running a new main

I was wondering if I could safely insulate the pipe from freeze ups.  There is enough room where another 8 in block wall can be built in front of the main whereby enclosing it between the two block walls leaving a space of about 5 inches.   My thought was to wrap the main with flexible pipe insulation, build the secondary wall up three coarses and fill the remaining void with sand or spray foam.  I would fill the concrete block cells of the second (outside) wall with spray foam insulation and cap the top of the area with blue stone slab.  The pipe would be about 24 inches below the stone slab and 11 inches from the exterior of the secondary wall face. 

Would this allow for sufficient thermal protection to prevent the pipe from freezing?

(The pipe can be seen at bottom behind shovels in photo)

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  1. Expert Member
    NICK KEENAN | | #1

    It's common to put sheets of EPS foam over the pipe where it can't be buried deeply enough. The rule of thumb is one inch of foam equals one foot of dirt. The foam should extend past the pipe one foot for every inch of thickness.

  2. Jon_R | | #2

    > wrap the main with flexible pipe insulation

    Insulate from the cold above, but leave exposed to the heat from below (or interior). If there is any doubt, then consider electrical heat.

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