New York / Nassau County
Score 21 · moderate · #55 of 62 in NY
Crawl space moisture in Nassau County, NY
Nassau County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 27% of acres — it averages 2 ft below grade.
- 1Water table 2 ft
- 2Wet soils 16%
- 3Moisture score 21
- 4EPA radon zone 3
Reading the Nassau County soil survey
The score of 21 combines four parts, each from the USDA survey: wet drainage classes contribute 18.9 points of 100 on their own scale, group D soils 29.2, a shallow water table 18.6, and flooding 14.9; the weights are on the methodology page. The dominant hydrologic group is A (33% of acres): high infiltration, low runoff (sands, gravels).
At 2 ft the seasonal water table is usually below a crawl-space floor, but the 27% of acres that report one are by definition the wettest parts of the county; on those lots, a wet spring can bring water close to the footings.
Nassau County against the rest of New York
Nassau County ranks 55 of 62 New York counties, 18 points below the state median of 39. That places it in the middle range, nationally and for the state. Statewide, 28% of mapped soil is in the wet drainage classes; here it is 16%, below the state figure — the score here comes from flooding and ponding rather than drainage class alone. After well drained, the next most common class is very poorly drained at 13%.
Flooding. 2.6% of acres with a flooding class are rated rare. That is a large flood-prone share; a crawl space in the floodplain needs flood vents under most local floodplain ordinances, which is a separate rule from R408 and can rule out a fully sealed design.
What it means for a crawl space here
In a moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those first.
Radon. EPA radon zone 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Nassau County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area NY059; drainage covers 34% of 209,900 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.