If you are trying to figure out the rules for an ADU permit in Texas, here is the single most important thing to understand before you do anything else. There is no statewide ADU law. Texas does not zone at the state level, counties generally cannot zone unincorporated land, and that leaves the rules almost entirely up to individual cities. The result is that an accessory dwelling unit that is legal by right in Houston might need a special exception in Dallas, sit under a strict size cap in San Antonio, and qualify for up to two units on a small lot in Austin. Same state, four completely different rulebooks.
So when someone asks "do I need a permit for an ADU in Texas," the honest answer is yes, almost always, and the rules that govern it depend on which side of a city limit line your lot sits on. Below is the city by city breakdown for the four biggest markets, plus what happens out in the unincorporated areas where a lot of Texas land actually is.
The one rule that applies everywhere: the building code
Whatever your city allows, the structure itself has to be built to code. Texas has adopted the International Residential Code for one and two family dwellings, and your city enforces it through plan review and inspections. For an ADU, the IRC is what turns a shed into legal habitable space. It sets the minimums for ceiling height, light and ventilation, emergency egress windows in sleeping rooms, smoke and carbon monoxide alarms, insulation, and the electrical, plumbing, and mechanical systems. That last point matters for budgeting. A real ADU is not just a building permit. You will typically pull a building permit plus separate electrical, plumbing, and mechanical permits, and each carries its own inspections before you can get a certificate of occupancy.
Keep that framework in mind as we go, because the zoning rules below sit on top of it. Zoning tells you whether you can build and how big. The code tells you how.
Austin: the most permissive big city in Texas right now
Austin rewrote its rulebook with the HOME Initiative, a set of code amendments the City Council approved in December 2023 and rolled out in two phases through 2024. The headline for Austin ADU rules is dramatic. You can now build up to three homes on a single family lot, which in practice means your main house plus as many as two ADUs, on lots as small as 2,500 square feet. ADUs are allowed across the SF-1, SF-2, and SF-3 districts, not just SF-3 the way they used to be, so a lot of properties that were locked out before now qualify.
Two old barriers are gone. Austin removed the off street parking requirement for these units, and it dropped the owner occupancy requirement, so you no longer have to live on the property to build or rent one. Size is generally governed by a cap in the range of 1,100 square feet combined with floor area ratio and impervious cover limits that scale with your lot, and the binding constraint on a smaller lot is often impervious cover rather than the square footage cap itself. A detached ADU has to sit at least 10 feet from the main house, and rear and side setbacks vary by district. If you have large heritage trees, budget time for a separate tree review, because Austin protects critical root zones aggressively.
Two cautions. Short term rental of an ADU built after October 1, 2015 is capped at 30 days per year, so the Airbnb math does not work the way some owners assume, although standard long term leases of 30 days or more are unrestricted. And parts of the HOME Initiative have been challenged in court, so while the rules are in effect in 2026, the legal picture is still moving. Confirm current zoning and the live ruleset for your specific parcel before you commit to a design. Permits run through the Austin Development Services Department.
Houston: no zoning, but deed restrictions run the show
Houston is the famous exception in American land use. It has no zoning ordinance at all, which means ADUs, known locally as garage apartments or quarters, are allowed by right almost anywhere in the city. The catch is that the thing standing between you and your ADU is usually not the city. It is your deed restrictions. These are private, recorded covenants that bind every lot in a subdivision, and Houston courts enforce them over city rules. A deed restriction can prohibit secondary structures, ban rentals, or impose its own height limits. Pull your deed restrictions through the Houston Planning and Development Department before you hire anyone or pay for plans, because this is the step that most often kills a project after money has already been spent.
When the deed allows it, the city rules are straightforward. Houston caps an ADU at 900 square feet, and every unit needs its own kitchen and bathroom. Rear and side setbacks are at least 5 feet, raised from the older 3 foot standard. You will need one dedicated off street parking space for the ADU on top of the two required for the main house, so plan for three total, and a garage conversion has to account for the parking it removes. One ADU is allowed per single family lot, and you cannot add one to a lot that already has two or more dwellings. Houston does not impose a citywide owner occupancy rule, though again your deed restrictions might. Accessory structures under 200 square feet and 15 feet tall are exempt from a building permit, but any habitable ADU is well past that and always requires one.
Dallas: allowed, but not by right
Dallas is where a lot of homeowners get tripped up, because an ADU is permitted in concept but not automatic. In most single family zones you cannot simply build one by right. You either need your neighborhood to carry an ADU Overlay, which is a zoning designation applied area by area, or you have to win a special exception from the Board of Adjustment for your specific lot. That is a discretionary, public process, and it is the single biggest difference between Dallas and Houston or Austin.
Once you have the right to build, Dallas caps the unit at 800 square feet. The city ties ADUs to owner presence. Either the main house or the ADU has to be owner occupied, and the unit that is not owner occupied has to be registered every year under the city's single family rental program, whether your tenant is a stranger or your own mother. The ADU cannot be sold separately from the main home. Setbacks depend on which approval path you took, so check your lot against the City of Dallas ADU requirements before you draw anything. Permits go through Dallas Development Services.
San Antonio: clear rules, smaller footprint, free plans
San Antonio sits in the middle. ADUs, widely called casitas here, are allowed in selected residential zoning districts under the city's Unified Development Code, and the city has actively encouraged them as a tool against the housing shortage. The detached size cap is 800 square feet, and the city does not impose an owner occupancy requirement. Setback and parking specifics vary by district and have shifted recently, so verify the current numbers for your zoning before designing, rather than trusting a blog figure.
The standout perk is practical. San Antonio's Development Services Department publishes a set of pre approved, permit ready casita plans, including compact designs in the range of 500 to 600 square feet. Building from a city approved plan can shorten review and cut design cost, which is a genuine head start most Texas cities do not offer. If your lot fits one of those designs, it is worth a serious look.
Outside city limits: the unincorporated areas
A surprising amount of Texas land sits in unincorporated county territory, and the rules there are almost the inverse of a city. Texas counties generally have no zoning authority, so there is usually no ordinance that specifically permits or prohibits an ADU. In Nueces County, for example, the county does not enforce zoning in unincorporated areas, so there is no county wide ADU rule at all. If your land falls inside Corpus Christi or another municipality, you follow that city's ordinance instead.
That sounds like freedom, and in some ways it is, but it comes with its own homework. Counties have only limited authority to enforce building codes in unincorporated areas, and many do not inspect residential construction or issue a certificate of occupancy. What you almost certainly will need is an on site sewage facility, or septic, permit if there is no public sewer, and you should still build to the IRC for the sake of financing, insurance, and resale. You should also check whether the property sits in a city's extraterritorial jurisdiction, because that can pull some municipal requirements onto land that looks fully rural on a map. The practical move is to call the county building or development office and the nearest city before assuming you can build with no oversight.
What this means for your project
The throughline across all four cities is that the answer is never generic. It is specific to your lot, your zoning district, and, in Houston especially, your deed restrictions. Two identical backyards a mile apart can have completely different rights. That is exactly why the costly mistakes happen during design rather than construction, when an owner pays for plans that the setback, the size cap, the overlay requirement, or a recorded covenant will not allow.
The right sequence is to confirm what you can build, then design to it. A focused zoning and code research report pins down your district's size limits, setbacks, parking, and approval path, and flags whether you are looking at a by right build or a Dallas style special exception. From there, a complete ADU permit package gets you a code compliant, submission ready set of drawings, and for a simpler backyard build an accessory structure permit may be the cleaner path. You can see the full scope of what we draft across the state on our residential services page.
Tell us your Texas city and lot, and we will confirm what you can build. One quick check now saves you from designing something your zoning was never going to approve.