New construction radon mitigation with no attic
We are initially building a very small (16×24) studio cabin with a single slant shed roof. The plans for the ceiling/roof consist of a layered superstructure somewhat along the lines of cathedral ceiling …meaning no attic space.
The structure is on an unvented crawl space CMU block wall foundation (dirt floor, no slab). We’re working to get our ducks in a line for encapsulation and radon mitigation prior to installing floor joists.
Best I understand, the code requires passive radon mitigation and also requires an electrical outlet to be installed in a viable location in the event a fan is needed. A radon fan cannot be within or below the conditioned space.
So if I’m correct this means we would either have to have an electrical outlet on the roof if the pipe went inside the wall cavity up through the roof, or else we have to install all of the pvc along an exterior wall so that the fan could be installed at a regular lower exterior electrical outlet.
Questions:
1) am I understanding code correctly?
2) if we were to run the pipe along the exterior, am I correct that a hole would be cut through the rim joist (in our case it would be a double rim)? Or how/where would it be best run to the outside?
3) if we run the pipe outside, (and potentially an eventual fan) the pictures I have seen with that method are so unattractive- what are the most effective suggestions for disguising it all to keep a streamlined exterior?
Thank you very much.
heather
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Replies
1- Pretty much, yes. You have to provide an accessible outlet in an area where the fan might sometime be installed if needed (i.e. if the passive system alone isn't enough to get you under the action level of 4 pCi/L. The best collection system is perforted pipe (usually the cheap corrugated stuff) in the gravel bed under the slab, with a 3" or 4" PVC pipe tied into that that goes up and out for venting.
2- Generally you'd go through the rim joist, but it depends on how the structure is built exactly what you'd go through. You need to get outside, then up above the roof line. My preference is to go up through the interior and out the roof, leaving a spot in the attic for a fan, but that's not always possible, in which case you'd run the pipe up the exterior somewhere.
3- Most of the exterior systems are retrofits, since it's a lot more labor to do a retrofit that is enclosed in walls (although sometimes a pipe can be run up through something more accessible like a closet). I don't see how you could mount a typical radon fan above the roof line, but there might be some that can be mounted that way that I'm not aware of. The fans usually connect to the pipe with rubber couplers, and they need some protection against rain coming directly into the fan outlet, so you couldn't just put a regular fan on the top of a pipe venting out through the roof -- the fan would have to be mounted lower somewhere where the top and bottom of the fan can connect to pipe for support.
To conceal an exterior line new construction, you could bump out a wall someplace like you'd do for a chimney or other type of larger vent. You could leave an access for a fan, but BE SURE the space is large enough to accomodate a fan. You are correct that the fan has to be outside of the building envelope though, so you can't put it in the basement (even though I see that all the time in online DIY pics and videos). The idea is that you don't want the fan to be pressurizing anything INSIDE the home that could then leak radon out into the house somewhere. With the fan outside, ALL leads leak INTO the pipe, which avoids any issues of radon leaks within the home.
Bill
Can you run the passive pipe out of the sealed crawl, up an exterior wall for 4' or so, then back into an interior wall, so it goes out and up?
Bill's idea of an unconditioned exterior bump out to conceal the pipe is better.
Another option would be to select a closet or room such as the bathroom and have the area above that be air separated from the conditioned space. You could then put the radon fan in this space.