Crawl spaces use sub-membrane depressurization: a sealed 20-mil liner over the exposed earth with a fan drawing soil gas from beneath it. Slab-on-grade homes use standard sub-slab depressurization, usually the simplest install of the three.
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Foundation type changes the method, the price, and how long the work takes, which is why any quote given before someone knows your foundation is a guess. A full basement is the common case in the Greater Columbus and Central Ohio housing stock and gets sub-slab depressurization: one or more suction points cored through the slab, pipe routed up and out, and a fan mounted outside the living envelope discharging above the eave line. A crawl space cannot be depressurized the same way, because there is no slab to draw through. The method is sub-membrane depressurization: a 20-mil polyethylene liner laid over the exposed earth, sealed to the crawl walls and around every pier, with the fan drawing from beneath the membrane. ANSI/AARST CCAH-2020-0523 requires the membrane sealing and a manometer verifying continuous negative pressure across it. The membrane work is why crawl-space mitigation is its own pricing tier at $1,800 to $3,500 rather than the $1,200 to $2,400 typical of a basement. Slab-on-grade is usually the least complicated and the cheapest, particularly on newer homes where an exterior wall is unobstructed and the pipe has a short clean route. Mixed foundations are common in the mix of pre-war stock in the older Columbus neighborhoods, mid-century ranches in the inner suburbs, and large 1990s-onward subdivisions in the outer counties and they need honest scoping. A house with a basement under half the footprint and a crawl space under the rest may need both methods, or a single system with a tie-in, depending on whether the two areas are connected below grade. That is a site visit question, not a phone question.