About Crawl Space Map

Crawl Space Map reads the USDA soil survey for every county — drainage class, hydrologic group, water-table depth, flooding — and turns it into a crawl-space moisture score, alongside the IRC R408 rules for venting and encapsulating.

How the site works

Every county figure comes from the USDA NRCS soil survey, read through Soil Data Access and weighted by acreage, with EPA's radon zone joined by county; the building-code figures are the International Residential Code's Section R408 as published by state agencies. The score's weights and every exclusion are on the methodology page.

Who it is for

Homeowners and buyers trying to judge whether a damp crawl space is the house or the ground; and anyone deciding between venting and sealing one. It sells nothing and gives no prices.

Corrections

If a figure is wrong or a source has changed, email hello@crawlspacemap.com with the page and a link. Corrections go into the data file and the check date updates with the next build.

Data version 2026-10-23.