Crawl spaces get sub-membrane depressurization: a sealed plastic membrane over the dirt with a fan drawing from beneath it. Slab and basement homes get sub-slab suction through a hole cored in the floor. Plenty of Central Ohio houses need both.
More detail
Ohio's standards set the crawl-space minimums: a membrane of at least 6 mil polyethylene or 3 mil cross-laminated, heavier where the crawl holds storage or gets regular foot traffic; seams overlapped at least 12 inches and sealed; edges fastened mechanically to walls and piers; and access doors gasketed but never sealed shut. Depressurizing a crawl without a membrane is allowed only when the space is inaccessible. The EPA rates sub-membrane suction at 50 to 99 percent reduction, against 0 to 50 for simply venting the crawl. In split-levels and ranches with additions, common in Hilliard, Whitehall, and Reynoldsburg, one fan can often serve both areas when the layout allows. Crawl systems sit in the $1,800 to $3,500 tier. See crawl space radon mitigation.