Foundation Soils (foundationsoils.com) is a reference site on the soil and water under US houses, launched in 2026 and built from USDA, NOAA, FEMA and Census data.
This repository holds the numbers behind the site as four CSV files: one row per US county, Texas city, Ohio city and soil series. The soil shares are computed from USDA's soil survey the same way on every row, so places can be compared with each other. Foundation Soils is not part of any foundation repair or waterproofing company. Articles titled "Foundation Soils" on contractor websites, including Foundation Recovery Systems and AquaGuard Foundation Solutions, belong to those companies.
| File | Rows | One row per |
|---|---|---|
counties.csv |
3,144 | county or county-equivalent in the 50 states and DC |
tx-cities.csv |
1,227 | active incorporated place in Texas |
oh-cities.csv |
922 | active incorporated place in Ohio |
soil-series.csv |
160 | soil series under the most US housing |
As of: soil survey versions to August 5, 2026; Drought Monitor map of September 29, 2026; FEMA flood records refreshed September 9, 2026; NOAA rain through August 2026; Census ACS 2020-2024 5-year.
page_url links the place's page on foundationsoils.com. It is filled for every place with a page; places without enough data to rate have none.
Shares are fractions from 0 to 1 of the place's mapped land (0.51 = 51%). A blank cell means the source has no value for that place, or the site doesn't show one (see the notes below).
Soil (all four files)
expansive_clay_share: share of mapped land where USDA's national interpretation "Dwellings without basements" lists shrink-swell as a limiting feature with a rating of 0.5 or more on its 0-to-1 scale.high_water_table_share: share of mapped land where USDA's "Dwellings with basements" interpretation lists depth to a saturated zone as a limiting feature with a rating of 0.5 or more (ground water about 2.5 to 6 feet down).septic_very_limited_share: share rated "very limited" for septic absorption fields.lep_weighted_avg_pct(places) andlep_median_pct(series): linear extensibility, the percent change in a soil's length between moist and oven-dry (USDA classes: under 3% low, 3-6% moderate, 6-9% high, 9% and up very high).top_soil_series,top_soil_series_share: the soil series covering the most land, and its share.soil_rated: false when USDA's soil survey maps too little of the place to rate it; the soil columns are blank.mapped_acres,soil_as_of: the land the shares are computed over, and the newest survey version used.
Drought: drought_d1_plus_pct is the percent of the county's area in D1 (moderate drought) or worse on the map of
drought_map_date; drought_weeks_d1_plus_last_52 counts the weeks in the last 52 with any D1 or worse. City files
carry the county's figure (county_drought_d1_plus_pct).
Flood losses (counties): flood_records_since_2016 counts NFIP loss records with a date of loss from January 1,
2016; flood_paid_records_since_2016 and flood_paid_usd_since_2016 count the records with a payment and the amount
paid for building, contents and compliance costs (gross, as reported); flood_records_per_10k_homes divides by
housing units; flood_latest_loss is the newest loss on record for the county.
Rain (counties): rain_normal_annual_in is the 1991-2020 average calendar-year total; rain_last12_in and
rain_last12_vs_normal_in are the 12 months ending rain_last12_end and their difference from that average.
Homes: housing_units, median_year_built, pre1980_share (built in 1979 or earlier) and median_home_value_usd
from the Census Bureau's American Community Survey. City figures are left blank for places with fewer than 100
housing units.
Soil series: mapped_acres and states where the series is mapped, clay_median_pct, drainage,
hydrologic_group and taxonomic_class from SSURGO, and a link to USDA's series description.
The Soil Survey Geographic Database (SSURGO), queried through USDA's Soil Data Access service. Each map unit's acres are weighted by each soil component's percentage of that map unit. Every component counts in the denominator, including urban land and water, which USDA doesn't rate, so a heavily built county can show lower shares than its soils alone would. County acres come from SSURGO's county overlap tables; where those can't be used (Connecticut's planning regions, split Alaska boroughs, survey areas without overlap acres) the Census county boundary is clipped against the soil map. City shares clip each Texas and Ohio city's Census boundary against the soil map with Soil Data Access spatial queries.
A soil rating describes the ground, not the condition of any house. No public dataset records foundation failures by place, and reinforced slab-on-ground construction has markedly reduced the shrink-swell limitation for small buildings (USDA Soil Survey Manual). Full method, checks against hand-confirmed values, and USDA's own wording: https://foundationsoils.com/sources/
- Soil: USDA NRCS SSURGO via Soil Data Access, https://sdmdataaccess.sc.egov.usda.gov/
- Drought: US Drought Monitor, https://droughtmonitor.unl.edu/. The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration.
- Flood losses: FEMA OpenFEMA, NFIP Redacted Claims v3, API endpoint https://www.fema.gov/api/open/v3/NfipClaims, refreshed by FEMA on September 9, 2026 and retrieved on September 28, 2026 at 21:10 UTC. This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
- Rain: NOAA NCEI county precipitation series (nClimDiv).
- Homes: US Census Bureau, American Community Survey (ACS 2020-2024 5-year).
- Boundaries: Census Bureau Gazetteer files and TIGERweb.
The federal source data (USDA NRCS, FEMA, NOAA NCEI and the Census Bureau) are works of the US government and in the
public domain in the United States. The Drought Monitor figures carry the credit line above. The compiled tables in
this repository are released under CC BY 4.0 (LICENSE): reuse them freely, with credit to Foundation Soils
(foundationsoils.com). CITATION.cff has the citation.
About the site and how it is paid for: https://foundationsoils.com/about/