What goes wrong in a Central Ohio house: soils, water, radon, termites and weather

What goes wrong in a Central Ohio house is already written down, county by county, by agencies that mapped this ground before the subdivisions went up. The word they repeat is wetness: the federal soil survey of Franklin County rates the county's two most extensive soils somewhat poorly drained and very poorly drained, names the building limitation as wetness and low strength, and rates their shrink-swell potential moderate. This page takes the causes one at a time in each agency's own category names, and sets beside each what the Residential Code of Ohio requires because of it. Every rating here is of mapped ground, a state or a county, never of a house.

Last updated September 2026 · Federal soil surveys and series descriptions, the state geological survey's karst map, the federal radon zone map and the 1988 to 1989 radon survey, the Residential Code of Ohio, FEMA's flood zone definitions and the Ohio hazard mitigation plan were read September 2026 · No prices on this page; the Estimate Builder carries those · Part of the knowledge base

What these ratings are, and what they are not

Every category name below belongs to an agency, and each rates ground, weather, a state or a county, never a house. The federal soil survey of Franklin County says of its own tables that the information is not site specific and does not eliminate the need for onsite investigation of the soils. Severe, in its definitions, means soil properties so unfavorable or so difficult to overcome that special design, significant increases in construction costs and possibly increased maintenance are required; it does not mean a house cannot stand there. Nothing here counts houses either: no source read counts how many Central Ohio houses have a wet basement, a sump pump, a radon system or termite damage.

The incidents behind particular Ohio rules are on the fires, floods and collapses page; dating a house standing in this ground is the field guide to era and style.

The ground the glaciers left, and the soil on top of it

The federal soil survey of Franklin County says the county was glaciated in at least two glacial periods, the Wisconsin ice sheet advancing twice, about 50,000 and about 16,000 years ago, each leaving a layer of till. The Ohio Division of Geological Survey defines till as material deposited directly by a glacier, unsorted sand, gravel, silt and clay; its sorted counterpart, outwash, forms Ohio's largest deposits along the Great Miami and Mad Rivers between Bellefontaine and Cincinnati and along the Scioto between Columbus and Portsmouth. The county's surface, the federal survey says, is mostly ground moraine, averaging about 50 feet of till over bedrock, a county-wide average and not a depth at any address.

In its acreage table the county's two most extensive soils are Kokomo silty clay loam, 10.6 percent of the county, and Crosby silt loam on 0 to 2 percent slopes, 9.4 percent. The Natural Resources Conservation Service classes Crosby and Bennington somewhat poorly drained, Kokomo very poorly drained and Miamian well drained. The survey's building site development table rates Crosby severe for dwellings with basements, for wetness and low strength, and puts its seasonal high water table between 12 and 36 inches down late in winter, in spring and in other extended wet periods, with potential frost action high.

The survey does not say what is most often said about this ground. It rates shrink-swell potential, the potential for volume change in a soil with a loss or gain in moisture, moderate in the subsoil of Crosby and moderate in Kokomo, on a scale whose higher classes are high and very high. The foundations chapter does reach the swelling case: section 401.4 lets the building official require a soil test where accepted soil science data indicate expansive soils are likely, and section 403.1.8 sends a foundation on soil the code's own tests call expansive to the Ohio Building Code. Central Ohio's mapped soil problem, in the survey's words, is wetness and low strength, not swelling clay, and the remedy its 1980 survey prints is written for the outside of the house: building sites should be landscaped for good surface drainage away from foundations. What Ohio's own clay and stone became is on the page about what Ohio made for houses.

Water at the foundation, and what the residential code requires

Section 405.1 of the Residential Code of Ohio, which prints its sections without the model code's R prefix, requires drains around concrete or masonry foundations that retain earth and enclose habitable or usable spaces below grade, at or below the top of the footing or below the bottom of the slab, on not less than 2 inches of washed gravel or crushed rock and covered with not less than 6 inches of the same. Its one exception is written for a soil type rather than a place, excusing the drain only on the clean gravels and sands its Table 405.1 calls Group I, which the silt loams, silty clay loams and clay loams mapped across most of Franklin County are not.

Section 406.1 then requires foundation walls enclosing spaces below grade to be dampproofed from the top of the footing up to the finished grade, and section 406.2 raises that to waterproofing in areas where a high water table or other severe soil-water conditions are known to exist, listing eight materials that satisfy it. The code names no Ohio place as such an area; that is the local building department's call. Both sections excuse an existing house where a supplemental interior foundation drainage system is installed and connected to a sump pump. Foundation drains, sump discharge and Blueprint Columbus belong to the sewer lateral page and the Columbus sewers page.

Karst, and where the state survey puts it

The Ohio Division of Geological Survey defines karst as a landform that develops on or in limestone, dolomite or gypsum by dissolution, marked by sinkholes, drainage through solution-enlarged fractures, and caves. On its map of known and probable karst it names the Scioto and Olentangy River gorges as one of Ohio's five most significant karst regions and says the uplands beside them, in northern Franklin and southern Delaware counties, include areas of well-developed, active karst terrain.

The survey says sinkhole concentrations of up to one sinkhole per acre are not uncommon in Concord, Scioto and Radnor Townships of Delaware County, the sinkholes ranging from about 10 to 100 feet across. It adds that because these uplands are among the most rapidly developing areas of the state, karst should be a consideration in site assessments for commercial and residential construction projects.

Radon, exactly as the agencies state it

The federal Environmental Protection Agency's Map of Radon Zones, developed in 1993, defines Zone 1 as counties with a predicted average indoor screening level greater than 4 picocuries per liter, Zone 2 as counties between 2 and 4, and Zone 3 as counties less than 2. Its own names for the three are highest, moderate and low potential.

Ohio's assignment is printed only as a color, and the agency publishes no county list; its own state document gives the assignment as a map image too. Read from the map's colors, 53 of Ohio's 88 counties are Zone 1 and 35 Zone 2, none Zone 3, and every county of the central band is Zone 1: Franklin, Delaware, Licking, Fairfield, Union, Madison and Pickaway. That is a reading of a map, not a sentence the agency wrote.

The map's own instruction: the Map of Radon Zones should not be used to determine if individual homes need to be tested, and all homes should be tested regardless of zone designation. The Ohio Department of Health's radon program says the same in its own words, that radon testing is the only way to know the radon levels in a home.

In the federal and state Residential Radon Survey of Ohio conducted in 1988 and 1989, 64 percent of the 170 screening measurements taken in Franklin County were above 4 picocuries per liter. The same table gives 72 percent of 29 measurements in Licking County, 61 percent of 31 in Fairfield, 57 percent of 7 in Pickaway, 55 percent of 20 in Delaware, 20 percent of 10 in Madison, and none of the 6 in Union County. Those were 2 to 7 day charcoal canister tests taken from the lowest level of each home, and the report warns that the samples may not be sufficient to statistically characterize the counties.

The state code says nothing. Neither the building planning chapter nor the foundations chapter of the Residential Code of Ohio contains a radon provision, and the code as printed in the Ohio Administrative Code has no appendix chapter at all, so the model code's optional radon appendix is not part of Ohio's. Radon-resistant construction here is a choice, not a requirement.

Termites and decay, in the code's own designations

The Residential Code of Ohio fills in the termite column of its climatic and geographic design criteria table with the words moderate to heavy. The state prints that in Table 301.2(1) rather than leaving it to a jurisdiction, and the table's footnote says the entry indicates the need for protection depending on whether there has been a history of local subterranean termite damage. It is a designation for a state, not a finding about a county or a house. Section 318.1 then requires protection by one or a combination of six methods: chemical termiticide treatment, a termite baiting system, pressure-preservative-treated wood, naturally durable termite-resistant wood, approved physical barriers, and cold-formed steel framing.

One well-known rule does not reach Ohio. Section 318.4's ban on foam plastic below grade applies where the probability of termite infestation is very heavy on the code's Figure 301.2(7), whose categories are very heavy, moderate to heavy, slight to moderate and none to slight. It shades Ohio moderate to heavy, matching the state's table; very heavy covers the Gulf and South Atlantic states and coastal California.

Decay is a separate rule, keyed to position rather than geography. Section 317.1 requires naturally durable or preservative-treated wood at seven locations, among them sills and sleepers on a slab in direct contact with the ground, and wood furring attached directly to the inside of a below-grade wall. That last, item 7, has an exception where an approved vapor retarder is applied between wall and framing, and it governs a finished basement wall built against masonry.

The weather, the flood maps and what the state's plan counts

Table 301.2(1) of the Residential Code of Ohio has eleven columns. Four carry a value for the whole state: an ultimate design wind speed of 115 miles per hour, a severe weathering classification, the termite entry of moderate to heavy, and ice barrier underlayment required, yes. Six are blank for the jurisdiction to fill in: ground snow load, seismic design category, frost line depth, flood hazards, air freezing index and mean annual temperature. The eleventh, winter design temperature, comes from the table's own footnote, a nine-station table giving Columbus 5,660 heating degree days a year and a design temperature of 5 degrees.

The 115 is an ultimate design wind speed, and the qualifier matters: section 301.2.1.3 converts it to about 90 nominal, so an older document showing 90 for the same place is not a different wind; the two should never be printed side by side without naming the convention. What Columbus fills into three of those columns, with the footing rule, is on the page on how these houses were built; the severe weathering classification beside them is the state's.

Footnote h to the same table says all jurisdictions in Ohio have a history of local damage from the effects of ice damming. The Department of Energy's Building America program gives the mechanism: snow is present on a roof, the roof deck under the snow reaches above freezing, and the melt water runs down the slope of the roof until it reaches the roof eave, where the deck is cold enough for it to refreeze. The dam backs meltwater up under the roofing, and escaping heat from the home is usually the source of the warming.

The Federal Emergency Management Agency defines the Special Flood Hazard Area as the area that will be inundated by the flood event having a 1-percent chance of being equaled or exceeded in any given year, also called the base flood or the 100-year flood. Shaded Zone X, the areas between the limits of the base flood and the 0.2-percent-annual-chance flood, sits outside the zone that triggers the federal flood insurance purchase requirement and inside a mapped flood; unshaded Zone X is areas outside the Special Flood Hazard Area and higher than that flood's elevation.

Section 301.2.4 of the Residential Code of Ohio refers buildings in flood hazard areas to its own flood section, and the climatic table leaves each jurisdiction to enter its flood insurance program dates and flood map panel numbers, so the rule for a particular house is local. The 1913 flood and the Franklinton floodwall are on the Franklinton page. Of the flood of January 1959 the United States Geological Survey records that at Columbus a levee along Dry Run, a small tributary of the Scioto River, was overtopped by the flood waters of the river, releasing water into the west side of the city, while Alum and Big Walnut Creeks were at unprecedented stages. The gage crests behind that record, the dams built after it and the flood maps' own dates are on the floods, dams, levees and floodwalls page.

The Ohio Emergency Management Agency's hazard plan maps 1,414 tornado touchdowns in Ohio between 1950 and 2023 and puts Franklin County second among the state's counties with 34, behind Van Wert at 39. For winter it counts days: 127 days with a severe winter weather event in Franklin County between January 1, 2003 and January 1, 2023, the second highest in its Region 2 behind Montgomery County's 132, against 104 in Delaware, 100 in Licking and 87 in Madison. The National Weather Service's Wilmington office puts Columbus's snowiest season at 67.8 inches in 1910 and its heaviest day of snow at 15.5 inches on March 8, 2008, in a record running from 1884 to the present.

What all of this asks of a bathroom

A basement bathroom sits in ground the federal survey rates severe for wetness and low strength, so drainage comes before plumbing, and the furring against a below-grade wall is on the code's own decay list. What goes under the finished floor is on the floors and subfloors page, the pipe that brings the water in on the supply pipes page, what hard water does on the water hardness page, hot water on the hot water page, the receptacles and the fan on the bathroom electrical page, and rain in a sanitary sewer on the sewer lateral page. Nothing here says what any one house needs.

Sources

Every figure, date and quotation on this page comes from one of these documents, read on the date given. Where two of them disagree, the page says so.

• U.S. Department of Agriculture, Soil Conservation Service, Soil Survey of Franklin County, Ohio, issued February 1980; read September 2026.
• Ohio Administrative Code, Ohio Laws (codes.ohio.gov), Rule 4101:8-3-01, Building planning (Residential Code of Ohio, chapter 3), effective July 1, 2019; read September 2026.
• Ohio Administrative Code, Ohio Laws (codes.ohio.gov), Rule 4101:8-4-01, Foundations (Residential Code of Ohio, chapter 4), effective March 1, 2024; read September 2026.
• Ohio Department of Natural Resources, Division of Geological Survey, Ohio Karst Areas (Known and probable karst in Ohio, Map EG-1), 1999, revised 2002 and 2006; read September 2026.
• United States Environmental Protection Agency, OHIO - EPA Map of Radon Zones, 1993 map; read September 2026.
• Federal Emergency Management Agency, Flood Zones, undated; read September 2026.
• Ohio Emergency Management Agency, State of Ohio Enhanced Hazard Mitigation Plan, Section 2.4, Winter Storm, revised February 2024; read September 2026.
• Ohio Emergency Management Agency, State of Ohio Enhanced Hazard Mitigation Plan, Section 2.3, Tornado, revised February 2024; read September 2026.
• Ohio Department of Natural Resources, Division of Geological Survey, GeoFacts 19: Sand and Gravel, revised 2023; read September 2026.
• U.S. Department of Agriculture, Natural Resources Conservation Service, Official Series Description: CROSBY (with MIAMIAN, KOKOMO and BENNINGTON), undated, maintained series; read September 2026.
• United States Environmental Protection Agency, EPA's Map of Radon Zones: Ohio (EPA 402-R-93-055), 1993; read September 2026.
• Ohio Department of Health, Radon Education Program, Radon Data (Ohio radon maps), page dated April 21, 2026; read September 2026.
• United States Geological Survey, Preliminary Geologic Radon Potential Assessment of Ohio (Open-File Report 93-292-E), 1993; read September 2026.
• Ohio Administrative Code, Ohio Laws (codes.ohio.gov), Ohio Administrative Code 4101:8 chapter index (Residential Code of Ohio), undated; read September 2026.
• U.S. Department of Energy, Building America Solution Center (Pacific Northwest National Laboratory), Construct Roofs and Attics for Ice Dam Prevention, last updated December 6, 2022; read September 2026.
• United States Geological Survey, Floods of January-February 1959 in Ohio (Geological Survey Circular 418), 1959; read September 2026.
• National Weather Service, Wilmington, Ohio forecast office, Columbus Snowfall Climatology: yearly and seasonal snowfall records for Columbus, last updated August 1, 2023; read September 2026.

Common questions