North Dakota / Nelson County
Score 39 · moderate · #10 of 53 in ND
Crawl space moisture in Nelson County, ND
Nelson County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 88% of acres — it averages 2.2 ft below grade.
- 1Water table 2.2 ft
- 2Wet soils 41%
- 3Moisture score 39
- 4EPA radon zone 1
Reading the Nelson County soil survey
The score of 39 combines four parts, each from the USDA survey: wet drainage classes contribute 44.3 points of 100 on their own scale, group D soils 26.1, a shallow water table 59, and flooding 2; the weights are on the methodology page. The dominant hydrologic group is B (38% of acres): moderate infiltration.
At 2.2 ft the seasonal water table is usually below a crawl-space floor, but the 88% 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.
Nelson County against the rest of North Dakota
Nelson County ranks 10 of 53 North Dakota counties, 15 points above the state median of 24. That puts it in the wettest quarter of the state. Statewide, 23% of mapped soil is in the wet drainage classes; here it is 41%, half again the state figure or more. After well drained, the next most common class is moderately well drained at 27%.
Flooding. 1.7% of acres with a flooding class are rated frequent; 0.4% of acres with a flooding class are rated occasional; 0.1% of acres with a flooding class are rated very rare. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods.
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. Nelson County is in EPA radon zone 1, the highest predicted potential. A sealed crawl space and a radon system share most of their parts — the liner, the sealed seams, a fan — so if you are encapsulating, test for radon first and design both together. EPA itself says the zone map is not a reason to skip testing in zones 2 and 3.
Near Nelson County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area ND063; drainage covers 98% of 648,320 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.