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Post date: Apr 30, 2015 2:53:58 AM
New Mexico has radon in the ground. We don’t want this radioactive, inert gas in our houses because it is one cause of lung cancer. While not a problem in the deep South or the West coast north of San Francisco, in the Rockies and across the northern states it is a serious problem.
So we ventilate under the floor and install a barrier so the gas does not come in through the floor. Today we laid four inches of one-inch round rock on top of the compacted fill that supports the house. This rock gets compacted now so it won’t settle after the house is built.We have been running the skid loader inside the foundations previously (see Utilities Started) but now is the time to leave the machine outside the foundation walls so that we can complete the foundation. So Eli brought in bucket loads of rock, which we spread, leveled, and compacted, then buckets of pea gravel (the darker material in the photo - to make the top of the rock smoother and better support the insulation), working from the east end of the house towards the road, where we had left nine feet of foundation to be formed at the end. The end is here.
We also had to form for a curb around the shower (visible on the right of the photo), so if there is a leak in the shower pan the escaped water will not rot the sills of the wall. This required higher forms and some cutting of holes in the foundation walls (made of styrofoam) to bond the floor of the shower to the foundation stem wall.
This layer of rock will have a pipe installed that runs up through the roof and draws the radon gas (or any gas, for that matter) up and out. Above the rock will be a four inch layer of styrofoam insulation, then two layers of polyethylene film, then another layer of four inch insulation. The drain pipes will be in the upper layer of insulation.
Why so much insulation? I’m not sure. The walls have R-40. Under the slab will also be R-40. But the coldest temperature outside the walls is normally 30°F, while the coldest temperature beneath the slab is about 50°F. So just one layer of R-20 insulation beneath the slab would lose the same amount of heat as the wall.
We expect the plumber tomorrow to install the drain pipes and the radon vent pipe. I plan to mark on my set of plans the location of each pipe the comes out of the foundation, and how deep it is.
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