Texas / Montgomery County
Score 45 · elevated · #14 of 209 in TX
Crawl space moisture in Montgomery County, TX
Montgomery County scores elevated because several moderate signals stack up rather than one dominant one. Where a seasonal water table is reported — 75% of acres — it averages 1.9 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.9 ft
- 2Wet soils 47%
- 3Moisture score 45
- 4EPA radon zone 3
Reading the Montgomery County soil survey
The score of 45 combines four parts, each from the USDA survey: wet drainage classes contribute 49.6 points of 100 on their own scale, group D soils 43, a shallow water table 53.2, and flooding 9.2; the weights are on the methodology page. The dominant hydrologic group is D (32% of acres): very slow infiltration, high runoff (clays, high water table).
A water table under two feet is the single most important number here. A crawl-space floor is usually 18 to 36 inches below the joists and often below outside grade, so in a wet season groundwater can stand at or above the crawl-space floor across much of Montgomery County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Montgomery County against the rest of Texas
Montgomery County ranks 14 of 209 Texas counties, 27 points above the state median of 18. That puts it in the wettest quarter of the state. Statewide, 6% of mapped soil is in the wet drainage classes; here it is 47%, half again the state figure or more. After moderately well drained, the next most common class is somewhat poorly drained at 29%.
Flooding. 8.7% of acres with a flooding class are rated frequent; 0.9% of acres with a flooding class are rated occasional; 0.2% of acres with a flooding class are rated rare. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods. Ponding — water standing at the surface with nowhere to go — affects 5.8% of acres.
What it means for a crawl space here
In an elevated county the soil supplies more moisture than average, but a vented crawl space can work if the ground is covered: the code lets vent area drop from 1 sq ft per 150 to 1 per 1500 with a Class I vapor retarder on the ground, which is an admission of how much moisture comes from below. Grading, gutters and a ground cover usually decide whether a crawl space here stays dry before any decision about sealing it.
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 Montgomery County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area TX339; drainage covers 94% of 688,742 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.