I have 2 questions. Hey George. Very valid question. We hear it all the time. Sure. Radon is roughly 7 times heavier than air. However, we are talking on such a small scale, that any slight breeze or natural air current will wisk it away. The main reason we want the vent stack to be up above the eve line more has to do with natural pressures of the structure. The lower on any building you go, the more air wants to get pulled in to said structure through what’s called the stack effect. Imagine any building as a piping system for radon. Where at the top, hot air is forcing itself out through the roof, and then to replace that air, the bottom is actively pulling air in from the surrounding soil. The whole point of a radon system (active of passive) is to try to give that air a path of least resistance so the radon (and moisture and other soil gases) is mitigated to a safe distance. That’s why they don’t call it radon removal, because we aren’t really removing it. We’re just giving it a nice path to dissipate outside. After that natural pressures prevent re-intrusion.
Prettiest option is always to put in the pipe during building so I applauded you know that. An ounce of prevention is worth a pound of cure.