Page 249 - Masonry and Concrete

Footings, Foundation Walls, Basements, and Slabs
248 CHAPTER SIX

In areas where radon gas from the soil is a potential problem, most
building codes require that basements, crawl spaces, and slabs-on-
grade be designed to resist radon entry and that the building be pre-
pared for post-construction radon mitigation, if necessary. Figure 6-51
shows CABO requirements for basement construction. Similar details
apply to crawl space and slab-on-grade foundations. One of the pri-
mary considerations is sealing the walls and slab to prevent gas entry.
Dampproofing, perimeter caulk, and a below-grade air barrier are
important elements. A 6-mil polyethylene sheet or a 3-mil cross-lami-
nated reinforced polyethylene sheet is acceptable for this use. The top
course of hollow concrete masonry foundation walls must be grouted
solid to prevent air leakage to the interior space above, and a 4-in.
layer of gravel below the slab acts as a gas-permeable layer which can
be mechanically vented if needed. All control joints, construction
joints, and isolation joints in concrete and masonry must be caulked.

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