Crawl space moisture in Union County, OR

Union County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 23% of acres — it averages 2.6 ft below grade.

Size venting or encapsulation

1Water table 2.6 ft
2Wet soils 11%
3Moisture score 20
4EPA radon zone 2

Share of mapped soil acres in Union County, OR by NRCS drainage class (dominant condition), bars to scale; wetter classes highlighted. Covers 99% of mapped acres.

Dominant drainage

Well drained

79% of acres

Group D soils

29%

slow infiltration

Flood-prone acres

14%

any flooding frequency

Ponding

acres where water ponds

Reading the Union County soil survey

The score of 20 combines four parts, each from the USDA survey: wet drainage classes contribute 10.7 points of 100 on their own scale, group D soils 47.5, a shallow water table 13.9, and flooding 7.7; the weights are on the methodology page. The dominant hydrologic group is C (62% of acres): slow infiltration (clay layers).

Hydrologic soil groups in Union 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 2.6 ft the seasonal water table is usually below a crawl-space floor, but the 23% 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.

Union County against the rest of Oregon

Union County ranks 13 of 34 Oregon counties, 2 points above the state median of 18. That places it in the middle range, nationally and for the state. Statewide, 7% of mapped soil is in the wet drainage classes; here it is 11%, half again the state figure or more. After well drained, the next most common class is somewhat poorly drained at 11%.

Flooding. 2.2% of acres with a flooding class are rated frequent; 7.8% of acres with a flooding class are rated occasional; 4.2% of acres with a flooding class are rated rare; 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. 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 Union County by score

Benton County 20 Columbia County 21Clackamas County 19Jackson County 19

All 34 Oregon counties

Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area OR625; drainage covers 99% of 651,646 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.