Professional
Home Inspection Service
Professional
Home Inspection Service
The home experts in Binghamton New York
Members of the American Society of Home Inspectors
by Keith Oberg, Professional Home Inspection Service
As installers of professional radon mitigation systems, we often find evidence of misguided
attempts by builders to prevent radon problems.
The most common builder strategy is to install drain tile below the basement floor with a tap
through the floor, available for the future installtion of a radon system, if necessary. This is not a
bad idea, however, a few pitfalls should be avoided.
Number one is don't tie this system to any drainage to daylight. This will prevent creation of
the vacuum necessary to successfully draw all radon from below the slab to the exterior.
Secondly, the tap should be compatible with 4" Schedule 20 PVC pipe and should be located in
an area that will allow a discrete exterior installation to above the roof line or a suitable route
through the house to above the roof line. Usually, locations in a mechanical room near the rear
wall or adjacent to the attached garage foundation work well. Remember to cap any tap through
the concrete floor or the radon levels will be even higher than otherwise.
Passive systems, where the builder installs piping from below the slab directly to the exterior,
or installs piping up through the house to the exterior, are almost never successful. They can't
overcome the stack affect which draws radon from the ground up through the living space. So,
the advice here is to make sure the passive system will easily allow the installation of a radon
fan. This means allowing enough space around the pipe in the attic or on the exterior to mount
the fan. The fan and couplings take up about 36" of vertical space and are roughly 12" in
diameter. The fan must be on a vertical section of pipe and should be above the living space or
on the exterior.
Another important point to remember is that any radon system requires a reasonably good
seal at the basement floor. Therefore, seal all floor penetrations, cracks, and any gaps at the
wall. A urethane caulk is preferable. This is especially important if finished materials are to be
installed on the lower level. Gaps left in the concrete floor for tub or shower drains, unsealed
sump pits and open floor drains to dry wells are common major radon entry points.
Ultimately, the only thing a builder really needs to do is provide adequate clean gravel (not
sand) below all portions of the slab and seal all penetrations, especially if finishing the lower
level.
Professional Home Inspection Service
1278 Vestal Avenue
Binghamton, New York 13903
