Radon travels in the soil gas under your foundation. A heated house sits at slightly lower pressure than the ground, so it draws that gas in through the floor-wall joint, cracks, sumps, drains, pipe openings, crawl-space dirt, and joints in block or stone walls.
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Central Ohio adds two local twists. First, most of the region is covered in glacial deposits, and the USGS found that the permeability of those deposits is the strongest control on how much radon reaches the surface: dense clay till slows it, while sand and gravel outwash along valleys like the Scioto and Olentangy lets it move freely. Second, the housing stock offers plenty of doors. A 1920s Clintonville basement may have mortared stone walls and a floor poured in sections, a postwar Whitehall ranch may sit over an open crawl, and a newer Hilliard split-level often has a slab and a crawl under one roof. Ohio's mitigation standards require the floor-wall joint, cracks, and utility openings to be sealed during an install, but sealing supports the fan; it never replaces it. See how a sump pit fits in.