Fairfax County, Virginia
A shallow water table limits basements on 33% of Fairfax County's mapped land, a higher share than 52% of US counties. Shrink-swell clay limits houses without basements on 6%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 340 flood losses here since 2016, 53% of them in buildings with basements. 44% of homes were built before 1980, against 50% nationally; the median home dates from 1983.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Fairfax County
| Expansive clay (limits slab homes) | 5.8% |
| High water table (limits basements) | 32.8% |
| Septic fields very limited | 67.1% |
| Clay swell (LEP, by area) | 2.5% |
| High-swell land (LEP 6%+) | 6.3% |
| Urban land, not rated | 15.1% |
| Mapped soil | 259,200 acres |
| Soil series | Share here | Series nationally: high water table |
|---|---|---|
| Glenelg | 18% | 0% |
| Wheaton | 13% | n/a |
| Codorus | 4% | n/a |
| Chantilly | 3% | n/a |
| Kingstowne | 3% | n/a |
| Sassafras | 3% | n/a |
How we count · survey areas VA059 (2025-09-05)
What the numbers mean here
On 33% of Fairfax County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 33.34 in, 9.90 in below the 1991-2020 average year of 43.24 in.
USDA rates 67% of the land very limited for septic absorption fields.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 43 of the last 52 weeks; the most was 100% of its area, in 32 weeks, most recently on the July 28, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 44.5% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
340 flood losses since 2016, $4.2 million paid. The worst year was 2019, with 100. Foundations of the buildings, where recorded: 53% basements, 10% slabs, 8% crawl spaces, 29% elevated. Median water depth outside the building: 7 in.
| Year | Flood losses |
|---|---|
| 2016 | 20 |
| 2017 | 20 |
| 2018 | 76 |
| 2019 | 100 |
| 2020 | 38 |
| 2021 | 47 |
| 2022 | 12 |
| 2023 | 5 |
| 2024 | 12 |
| 2025 | 8 |
| 2026 to date | 2 |
Rain
| Average year, 1991-2020 | 43.24 in |
| 12 months to August 2026 | 33.34 in (-9.90) |
| 2025 | 33.89 in (-9.35) |
| Wettest year since 1895 | 2003: 63.82 in |
| Driest year since 1895 | 1930: 20.28 in |
| Days with 1 inch or more, normal at VIENNA (4 mi away) | 10.2 |
Homes
| Housing units | 430,047 |
| Median year built | 1983 |
| Built before 1980 | 44% |
| Built 2000 or later | 20% |
| Owner-occupied | 69% |
| Median value, owner-occupied | $732,800 |
| Single-family detached | 46% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Fairfax city, VA | 2 mi | 2% | 10% |
| Falls Church city, VA | 6 mi | 0% | 13% |
| Arlington County, VA | 10 mi | 0% | 3% |
| Manassas Park city, VA | 10 mi | 0% | 16% |
| Alexandria city, VA | 10 mi | 3% | 44% |
| Manassas city, VA | 13 mi | 0% | 26% |
| Prince William County, VA | 14 mi | 9% | 35% |
| District of Columbia, DC | 15 mi | 0% | 9% |
Sources: USDA SSURGO (September 5, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status