Score 34 · moderate · #1 of 8 in NH

Crawl space moisture in Coos County, NH

Coos County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 75% of acres — it averages 2 ft below grade.

Size venting or encapsulation

1Water table 2 ft
2Wet soils 18%
3Moisture score 34
4EPA radon zone 2

Share of mapped soil acres in Coos County, NH by NRCS drainage class (dominant condition), bars to scale; wetter classes highlighted. Covers 98% of mapped acres.

Dominant drainage

Well drained

50% of acres

Group D soils

41%

slow infiltration

Flood-prone acres

any flooding frequency

Ponding

0.4%

acres where water ponds

Reading the Coos County soil survey

The score of 34 combines four parts, each from the USDA survey: wet drainage classes contribute 27.2 points of 100 on their own scale, group D soils 40.4, a shallow water table 51.9, and flooding 1.9; the weights are on the methodology page. The dominant hydrologic group is C (32% of acres): slow infiltration (clay layers).

Hydrologic soil groups in Coos County by share of acres, columns to scale. Group D and dual groups (x/D) shed water slowly and hold it near the surface.

At 2 ft the seasonal water table is usually below a crawl-space floor, but the 75% 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.

Coos County against the rest of New Hampshire

Coos County ranks 1 of 8 New Hampshire counties, 11 points above the state median of 23. Only no other county in the state scores higher. Statewide, 14% of mapped soil is in the wet drainage classes; here it is 18%. After well drained, the next most common class is moderately well drained at 27%.

Flooding. 1.5% of acres with a flooding class are rated frequent; 0.7% of acres with a flooding class are rated occasional. 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. EPA radon zone 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.

Near Coos County by score

Rockingham County 27 Strafford County 27 Carroll County 23Cheshire County 19

All 8 New Hampshire counties

Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area NH607; drainage covers 98% of 937,533 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.