St. Louis County, MO Shrink-Swell Risk
St. Louis County, MO's soil, for shrink-swell risk
Moderate
St. Louis County, MO: USDA's soil survey rates 70.6% of the county "Moderate" for shrink-swell potential (3.3% linear extensibility). Conventional foundations are the reasonable expectation here, with routine moisture-control practice rather than special engineering.
What St. Louis County's reading doesn't cover
Two lots a mile apart in St. Louis County can carry different soil, even though they share one countywide reading. The real answer for one lot is still a site-specific geotechnical report, running about $1,000-$5,000 (typically near $2,700).
What it costs to find out, versus to ignore it
With St. Louis County, MO rating "Moderate", a geotechnical report is still worthwhile before a build, just less urgent than in a high-risk county. A geotechnical report runs $1,000-$5,000, typically around $2,700. Foundation repair, if a specific lot turns out to differ from the county average, runs $5,000-$15,000.
How St. Louis County, MO compares
Nationally, St. Louis County, MO is the 969-most-constrained of 3,085 rated counties for shrink-swell soil. Within Missouri alone it ranks 69 of 114. The county spans 509 square miles, home to 992,929 people.
See how another county compares
Orleans Parish, LA carries this site's most-constrained reading. Howard County, MD and Mountrail County, ND are worth a look for comparison.
How this reading is built, and its real limits · Moisture management: the cheap fix that works on any soil
More of Missouri
Every county in Missouri is on this site, including Newton County, MO and Chariton County, MO. The full underlying dataset is downloadable directly, one row per county.