What Drives the Scope of Residential Structural Design in Texas

What Decides the Scope of a Residential Structural Design Job?

Start with the ground. Section R401.4 of the 2021 International Residential Code leaves it to the building official to require a soil test where accepted soil science says a site is likely to have expansive, compressible or shifting soil. Section R403.1.8 then sends foundations and slabs on expansive soil to the International Building Code's engineering provisions, with one way out: a system that has performed well in similar soil, if the building official accepts it. That is why soil causes the widest swings in how much design work a lot needs.

Next, what you are building. A new house needs a whole foundation plan. An addition has to meet a foundation that either moved or did not, and the design has to deal with whichever it is. Footprint and load path come third: a one-story slab with short spans raises fewer questions than a two-story house with a long open room. Last is the permit office. It decides how many sheets must be sealed, which code edition governs, and whether an engineer of record has to return to the site.

Those four are why two quotes for two lots on one street can differ, and they give you something to ask when a number shows up with no reasons attached.

Does Texas Law Make You Hire an Engineer for a House?

Less often than people assume, and in a way worth reading yourself. Occupations Code § 1001.056 exempts a person from the licensing requirement when they are drawing plans or specifications for a private dwelling, as long as they do not represent that engineering services are offered to the public. So a designer or builder can draw a house without an engineer in the loop, in general.

Then comes subsection (c)(2), which pulls the exemption back for one case: engineering design of a residential slab on soil that the International Residential Code, as the city applies it, calls expansive. Unless the work meets that city's code requirements, the exemption is gone. So when the lot sits on that kind of clay, the slab stops being a drafting job. How your city wants it answered is a question for the permit office.

Cities answer in different ways. The City of Waco's permit page says foundations on expansive soil are to be investigated and designed by a registered engineer. It adds that an addition needs an engineered foundation plan when its foundation system differs from the existing one, when the existing foundation has failed, and for any foundation of 500 square feet or larger on a shop, storage building or residential addition. And it says an engineer of record must inspect an engineered foundation before the pour and then file a sealed, signed and dated letter before the final building inspection. We cite Waco because its page states the rules plainly. It is outside the North Texas area where HGS Engineering does inspections, and the city you build in may write them differently.

How Expansive Is the Ground Where You Are Building?

The code's test for expansive soil is a plasticity index of 15 or greater, together with fine-particle and clay-size thresholds, or a swell test. The USDA reports a related measure, linear extensibility, for every mapped soil. We pulled it from the Soil Data Access service for seven North Texas counties on October 16, 2026. In 6 of the 7, more than half of the rated soil acres fall in the high or very high shrink-swell classes. Collin County is highest at 74.5% and Parker County is lowest at 9.3%.

Your lot is not a county. Soil can change in a few hundred feet, and the survey leaves a share of acres unrated. But with numbers like these, a design engineer in this region starts with the clay. Got a soil report for your lot? Send it along. Don't have one? Say so up front, and find out whether the office takes presumptive values or wants a test.

What Does Texas-Based Mean on the State Roster?

The board's firm roster gives each registered firm an address, and you can filter on the state. Of 12,617 active registrations in the file saved on October 16, 2026, 7,390 (58.6%) have a Texas address. Narrow it to firms with "structural" in the registered name and the picture changes: 413 active, of which 192 (46.5%) are in Texas and 221 are not. CA has 39, FL has 16, AZ has 13.

Austin and Houston together hold 52 of the registrations charted. Waxahachie, with 4, is the only charted city that has a service-area page on this site, so a firm's presence on the chart says little about whether it works in your county.

The counts rest on one field, the registered address. That tells you where a firm is registered. It says nothing about quality, and nothing about who holds the individual license. Ask for the sealing engineer's name, then look it up on the individual roster linked from the Rosters page in Sources.

What Should Any Texas Engineer Put in Writing Before You Pay?

Rule 137.33(f) of the board requires the seal, original signature and date on the final version of engineering work before it leaves the engineer's control, including the title sheet of bound reports and each original sheet of plans or drawings. Row 7 follows from that rule, and the other seven rows are our reading of what lets two quotes be compared.

1. The deliverables, sheet by sheet. Foundation plan, details, framing plan, calculations if the permit office wants them. A quote that says "structural package" has not told you what you are buying. A foundation-only set and a foundation plus framing set are different jobs, so name which sheets each quote covers before you set two side by side.
2. The city and the code edition. Texas cities adopt codes and amendments locally, so the design is for a named jurisdiction.
3. Where the soil data comes from. A report you supply, a test the engineer orders, or an assumed value the permit office accepts. Each changes the scope.
4. What is excluded. Grading, drainage design, a site visit, a separate retaining wall, an architect's drawings.
5. Plan-review comments. Whether answering the permit office's comments is part of the job, and how many rounds.
6. Field follow-up. Whether an engineer of record inspects before the pour or writes a letter afterward, if your city asks for one.
7. The engineer who seals. A name, a Texas license and a signature on the sheets, not only a firm name.
8. The format you receive. Sealed PDF, paper set, or both, and who files with the permit office.

How Does HGS Engineering Handle a Design Request?

Read this part as a firm describing itself. HGS Engineering has been registered with the board since 2019, in Arlington, and its registration runs to January 31, 2029 on the roster saved October 16, 2026. Heath Salmon, PE seals the structural drawings. Design work covers foundations, framing, retaining walls and plot plans across Texas and Oklahoma, and it is independent of any repair contractor.

The design request page asks for the client and contractor details, the project address and a link to whatever you already have: CAD files and drawing sets, soil and geotechnical reports, site plans and surveys, architectural plans and photos of existing conditions. It takes a link rather than file uploads, and nothing on the list is required to start. The firm replies with a quote and availability. You can also write to projects@hgsengineering.com with the project type, location and scope.

For how to compare firms on a foundation repair report rather than on design, see the guide to comparing residential structural engineers in Texas. The structural design page lists the four design areas, and the North Texas soil data shows the county figures behind the section above.

How Were These Numbers Made?

Method: a script reads the board's roster file and the saved USDA county summary, both committed to this site's repository, and writes the counts to a summary file. Active means the expiry date is after October 17, 2026. A Texas address means the state field reads TX. Structural in the name means the registered name contains the word. The soil classes are the depth-weighted linear extensibility classes described on the soil data page. Each cited page was fetched with curl on October 17, 2026 and saved with its HTTP status. A gate reruns the script before each build.