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Knollwood, Texas
Inside Knollwood's city limits, shrink-swell clay limits houses without basements on 76% of mapped land, higher than 80% of Texas cities. A shallow water table limits basements on 0%.
That clay share is above Grayson County's 60%. FEMA's flood data list 39 flood losses since 2016 in ZIP code 75092 overlapping the city. Of its 418 homes, 3% were built before 1980; the median dates from 2007.
Data as of October 13, 2026 · sources · in Grayson County
expansive clay: shrink-swell limits slab homes
high water table: limits basements
flood losses since 2016 in 1 overlapping ZIP
of homes built before 1980
Foundation repair in Knollwood
Foundation repair in Knollwood: shrink-swell clay limits slab homes on 76% of Knollwood's mapped land, more than in 80% of Texas cities.
| Who designs the repair | The ASCE Texas Section's repair guidelines say a Texas-licensed engineer should evaluate the foundation and design the repair (2022 guidelines) |
| Prices | Cost guide ranges compared |
Soil under Knollwood city limits
| Expansive clay (limits slab homes) | 75.6% |
| High water table (limits basements) | 0.0% |
| Septic fields very limited | 88.0% |
| Clay swell (LEP, by area) | 9.2% |
| High-swell land (LEP 6%+) | 54.6% |
| Mapped soil | 206 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Heiden | 39% | 80% |
| Austin | 21% | 93% |
| Houston Black | 14% | 91% |
| Fairlie | 10% | 70% |
| Howe | 6% | n/a |
| Whitewright | 4% | n/a |
What the numbers mean here
Clay swell averages a linear extensibility of 9.2% by land area here, and 55% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 76% of the mapped land.
Clay shrinks as it dries: 100% of Grayson County is in drought on the latest map, and 76% of Knollwood's mapped land has shrink-swell clay.
USDA rates 88% of the land very limited for septic absorption fields.
Drought in Grayson County
100% of Grayson County is in drought (D1 or worse) on the October 13, 2026 map. County detail.
Flood losses by ZIP code
FEMA flood records since 2016 in the ZIP codes that overlap Knollwood. ZIP areas reach past city limits.
| ZIP | Share of city land | Flood losses | Paid |
|---|---|---|---|
| 75092 | 100% | 39 | $1.5 million |
Homes in Knollwood
| Housing units | 418 |
| Median year built | 2007 |
| Built before 1980 | 3% |
| Built 2000 or later | 78% |
| Owner-occupied | 31% |
| Single-family detached | 1% |
Nearby cities
Sources: USDA SSURGO (August 5, 2026) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · Census ACS 2020-2024. Methods · Data status