Why Do Foundations Crack in Collin County?
Collin County has the highest share of high shrink-swell soil of the seven, and one soil name covers nearly half of the rated land.
Foundations crack in Collin County because 74.5% of its rated soil, by acre, is high or very high shrink-swell clay, the highest share of the seven counties, and 65.5% is in the very high class. HGS Engineering, PLLC (Texas Firm #21268) finds that Houston Black alone covers 210,429 acres of that. Plano is the city the firm has a page for.
Reviewed by Heath Salmon, PE, October 16, 2026. Soil data downloaded 2026-10-16, drought data downloaded 2026-10-16.
What Does the Soil Survey Say About Collin County?
Collin County splits 3.9% low, 21.6% moderate, 9% high and 65.5% very high, so about two thirds of the rated ground is in the most active class. Almost nothing is in the low class. A Collin County house has the highest chance in the study of sitting on clay that moves a great deal.
The survey lists only 85 components in the county, the fewest of the seven, against 300 in Tarrant. That is a much more uniform county: one clay, Houston Black, covers a very large part of it, and its behaviour is the county's behaviour.
The effect is on the whole structure. A brick veneer cracks at corners and above windows, doors begin to stick, and a floor develops a dish or a ridge as the middle of the slab moves against the edges. Those are what the report records and measures.
| Class | Rated acres | Share of rated acres |
|---|---|---|
| Low | 18,141 | 3.9% |
| Moderate | 100,439 | 21.6% |
| High | 41,887 | 9% |
| Very high | 304,383 | 65.5% |
| High plus very high | 346,270 | 74.5% |
| Not rated (urban land, water, pits) | 102,292 | 18% of all acres |
| Rank among the seven counties, high plus very high | 1 of 7 | |
Which Collin County Soils Carry the High Ratings?
Houston Black accounts for 210,429 acres of high or very high rating, the most for any single soil in the study. The next are Heiden (45,880), Tinn (35,997) and Burleson (13,738). The table shows the top five.
18% of the county is unrated. The ratings cover most of what is under a Collin County house, but not fill brought in for development.
| Soil name | High or very high acres |
|---|---|
| Houston Black | 210,429 |
| Heiden | 45,880 |
| Tinn | 35,997 |
| Burleson | 13,738 |
| Lewisville | 12,044 |
How Dry Has Collin County Been Since 2021?
Collin County had the fewest drought weeks of the seven. Some of its land was in D2 or worse in 51 of 262 weeks between 2021-10-12 and 2026-10-13, half or more in 36 weeks and half or more in D3 or worse in 14 weeks. The mean share in D2 or worse was 13.5%.
The calendar counts were 24 weeks with any D2 in 2022, 18 in 2023 and 8 so far in 2026. On the 2026-10-13 map, 48.09% of the county is in D2 or worse. With this much active clay, the ordinary seasonal swing is enough to move a slab, drought or not.
| Weeks counted | 262 |
|---|---|
| Weeks with any land in D2 (severe) or worse | 51 |
| Weeks with half or more of the county in D2 or worse | 36 |
| Weeks with half or more in D3 (extreme) or worse | 14 |
| Mean share of the county in D2 or worse | 13.5% |
| Latest week (2026-10-13): in D2 or worse, in D3 or worse | 48.09% and 4.19% |
| Weeks with any D2 in 2021 | 0 |
| Weeks with any D2 in 2022 | 24 |
| Weeks with any D2 in 2023 | 18 |
| Weeks with any D2 in 2024 | 1 |
| Weeks with any D2 in 2025 | 0 |
| Weeks with any D2 in 2026 | 8 |
What Does an Inspection Do With This Information?
On a Collin County house the engineer looks first at moisture management: grade, gutters, irrigation near the wall, trees and plumbing. Floor level readings and crack patterns show what the clay has already done. The sealed report states what was seen and recommends drainage changes where they apply.
The firm repairs nothing, and the fee for a Collin County inspection is quoted by email on request.
See the foundation inspection service page or use the request form.
How Were These Numbers Made?
Method: for each soil component in the Collin County SSURGO survey, the script averages linear extensibility over the top 100 centimeters, weighted by horizon depth. The average puts the component in an NRCS class: low under 3 percent, moderate 3 to under 6, high 6 to under 9, very high 9 or more. Acres are the map unit's acres times the component's percent of the unit, and components with no reading are left out of the percentages. The Drought Monitor figures are weekly county statistics. Both raw pulls are committed with the scripts, and a gate re-runs them before each build. A soil survey describes a county, never a single lot.
Where Does the Firm Work in Collin County?
- Foundation inspection in Plano, TX
- Foundation inspection service
- Other counties: Tarrant, Dallas, Johnson, Ellis, Parker, Denton
Frequently Asked Questions
Why do foundations crack in Collin County?
Because 74.5% of rated acres are high or very high shrink-swell clay and 65.5% are very high. A slab on that clay moves whenever its water content changes unevenly.
Is Collin County really the worst of the seven?
On this measure, yes: 74.5% against 71.7% in Ellis County and 63.9% in Dallas County. The measure is acres of soil, not houses with problems.
Does the firm serve Plano?
Yes. The firm has a Plano page and takes requests across Collin County by email.
What is the Houston Black soil?
It is one of the named soils in the NRCS survey, and the data shows it rated high or very high on 210,429 acres in Collin County. The firm takes no position on a soil name beyond the rating.
Sources
- USDA Natural Resources Conservation Service, Soil Data Access web service (SSURGO tabular data)Linear extensibility (lep_r), map unit acres and component percent for the seven counties, queried on 2026-10-16.
- National Drought Mitigation Center, University of Nebraska-Lincoln, U.S. Drought Monitor data services, county statisticsWeekly percent of each county in D2 (severe) or worse and D3 (extreme) or worse, October 2021 to October 2026.
- Texas Board of Professional Engineers and Land Surveyors, Engineering Firm RegistrationThe firm registration number and the licensed engineer seal.
- Texas Section, American Society of Civil Engineers, Guidelines for the Evaluation and Repair of Residential Foundations, Version 3Foundation evaluation practice, drainage away from the foundation and North Texas soil movement.
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