Crawlspace detailing is important in every home. When you’re building in Teton Valley Idaho, like I do, it is even more critical to get the details right. Our valley floor is at the foot on the Teton, Big Hole, and Palisades Mountain Ranges. The homes on the valley floor are in Climate Zone 6, while the hillside homes in the mountains are in Climate Zone 7. Besides harsh elements, and temperatures that drop below -30°F, we also have some of the highest radon levels in Idaho; and Idaho has some of the highest levels in the U.S. The average national indoor radon level is 1.3pCi/L. The average in Teton County is 10.5 pCi/L, which is over double the EPA’s recommended limit of 4.0 pCi/L.
Radon gas is produced as granite rock decomposes below the surface. A properly detailed passive radon mitigation system will create a barrier that will not allow these gases into the house and provides a path for gas to escape in a vent pipe exiting the roof of the house.
We begin this process before pouring footings. At interior footing locations, we must hand-dig for a 6-in. sleeve to be placed under the footing, near the exterior foundation wall. This will allow our 6-in. perforated radon gas collection pipe to be run around the entire perimeter of the crawlspace, after the foundation walls are poured. Then we cover the pipe with clean gravel or pea stone.
The next step is to install a vapor barrier to completely seal the crawlspace from the layer below, which is where the radon gases will accumulate. We run 2-ft. strips of 10-mil. polyethylene over the interior footings before framing the pony walls on top. This way, the vapor barrier…
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