October 31: After the plumbing was roughed in, a 6” layer of clear stone was laid down. This gravel base is an important stop-gap between potentially saturated soil and the slab I want to stay high and dry. It functions as a capillary break by interrupting the upward movement of water. It also was to become my “radon bed”.
Radon is an invisible, odorless, radioactive gas and the leading cause of lung cancer in non-smokers. According to the Sauk County Health Department, homes in any geographic location can test high—even when their neighbors house tests clean. In my zip code, 68% of homes tested need to install some type of radon mitigation system. Homes built on sandy soils, and homes built on a slab (like mine) are less likely to test high, but the possibility remains. The EPA recommends testing every 5 years, but many experts say testing should be done more frequently—even continuously.
The plumber set a horizontal PVC “tee” fitting into the gravel bed and glued it to a vertical 4” PVC pipe stub. Later, I’ll seal the pipe where it passes through the slab and cap it tightly. Once I move in, I’ll get both a short-term and a long-term radon test kit (readily available online or through the Health Department). Should my home test high, I’ll extend the PVC pipe through the mechanical/storage room and out the north wall terminating just under the roof eave. Any radon gas that seeps up from the ground and into the air pockets between the gravel will be drawn through the pipe and out into the atmosphere where it dilutes to safe levels. Besides radon, any humidity, mold, mildew, methane, pesticide gases, and VOC’s (volatile organic compounds) can make a speedy escape.
This set-up is called a passive system. It relies on the natural air pressure differentials between the interior of a building and the soil below. The “draw” can be accelerated by routing the radon pipe through a warm room, by increasing its height, and by keeping it straight.After extending the radon pipe, I’ll run another test. Should my home continue show elevated levels, I’ll hire a radon mitigation contractor to connect a fan to the pipe terminus. This fan must be located outside the living space in case it malfunctions and leaks gas. In most homes it can be hidden from view in a vented attic. Because my home has a vaulted ceiling and no attic, the fan would have to be mounted on the outside of the house.
In my mind, planning for radon is “best practice” and not an extra cost. It’s consistent with my goals for resource-efficient and healthful construction. It takes the long view by employing a strategy with modest up-front costs as a hedge against later, more expensive interventions.