Q: When you’re mitigating radon gas, is there a way to prep a house to avoid running an ugly pipe up the exterior façade?
A: Josh Girard, who owns and operates North Country Construction, in Jericho, Vt., responds: In retrofit situations, it’s sometimes hard to avoid using an exterior pipe, but with new construction, it’s fairly easy and inexpensive to do.
I build in northwestern Vermont in Radon Zone 2 where radon levels can vary widely, even from one lot to another within the same development. The predicted average indoor radon screening levels can range from 2 to 4 picocuries per liter (pCi/L)—meaning houses have a “moderate potential” for the presence of radon gas, according to the EPA. So as a matter of course with all new construction, I rough in a dedicated radon stack in every house I build in case a house tests positive for radon.
I tie the radon stack into the under-slab drainage system from the get-go. This beats a future retrofit situation of having to core through the concrete floor and install a single pipe down into the sub-slab gravel—that approach will mitigate radon gas, but it will be far less effective than tying the stack into the drainage system.
From the perforated sub-slab piping, I stub up a 4-inch piece of pipe into the basement (the poly vapor barrier is taped to the pipe and the slab is poured around it).
The plumbers take it from there and reduce the pipe down to a 3-inch PVC schedule 40 vent pipe. The pipe is then typically run through the exterior wall into the attic space. From there, it’s run through the roof and flashed with a standard roof vent boot.
A radon fan can be easily cut into the stack, if needed; I typically install the fans in the basement.
Although it’s another roof penetration I have to account for, a dedicated stack is cheap radon-mitigation insurance. A ready-to-go remedy beats an ugly pipe run up the exterior façade every time.
Photos and illustration: Tim Healey
