Radon Pipe vs Wastewater Pipe – GreenBuildingAdvisor

Hello All:

We will be breaking ground in 2 months (May 2026) for our 1,500 sq ft, 2 story home in western NY State. But we have an issue with the radon mitigation system to be installed under the basement floor slab.

We intend to put in a 5-inch layer of washed stone (grains approx 1/2″ to 3/4″) with 4-inch perforated pipe to collect radon and exhaust out through a vent pipe in the roof. We intend to use passive venting since we live near the top of a hill and have plenty of wind for Bernoulli effect.

But we have an issue with the under-slab wastewater drainpipe, which will extend across the entire width of the foundation (see images). The septic tank is off to the right side of the foundation, and we need a floor drain all the way over on the left side. The drainpipe blocks the path of a radon collection pipe for most of its length, thus cutting off the upper part of the foundation.

(note that I can’t get images to attach to this post so I have included links to external images below)

It seems there are 2 possible arrangements:

Confine the radon collection pipe to the region below (in the image) the wastewater drainpipe, relying upon the permeability of the stone to allow radon to flow from the upper region to the collection pipe.

Cross the radon collection pipe over the wastewater drainpipe at its lowest point, just before it exits the foundation. Due to the incline of the wastewater pipe, there should be enough room here between the underside of the slab and the top of the wastewater pipe for the radon pipe to fit through. Then the radon pipe can be extended into the area in the upper part of the foundation.

We are wondering if it’s worth the extra effort to extend the radon pipe all the way into the upper part of the foundation, especially since it will be a long way around the pipe circuit for the gas to travel to the vent? Or would it be effective to just put collection pipe in the lower part of the foundation only, and rely upon the gas flowing through the permeable layer of stone to get to the collection pipe?

Any thoughts on this question are much appreciated.