Texas backyards are getting busier. From garage conversions in East Austin to detached cottages in Houston Heights and casitas tucked behind San Antonio bungalows, accessory dwelling units have become one of the fastest-growing residential projects in the state. Some homeowners want rental income. Others need a place for aging parents or a college-age kid who’s not quite ready to fly the nest. A few just want a quiet home office that isn’t ten feet from the laundry room.
Whatever your reason, building an ADU in Texas comes with real rules, real costs, and real risk if you hire the wrong builder. Here’s what you need to know before you break ground.
What Counts as an ADU in Texas?
An accessory dwelling unit is a secondary, self-contained living space on the same lot as a primary single-family home. To qualify as an ADU, it generally needs its own kitchen, bathroom, and sleeping area, plus a separate entrance. In Texas, you’ll see them in three main forms:
- Detached ADUs — standalone backyard cottages or casitas
- Attached ADUs — additions that share a wall with the main house
- Conversion ADUs — garages, basements, or attics converted into living space
Texas doesn’t have a single statewide ADU law. Rules are set by city and county, which means the same backyard cottage Texas project can be straightforward in Austin and a permitting nightmare two hours away.
ADU Rules by City: What to Expect
Austin
Austin is the most ADU-friendly major city in Texas. Recent code changes allow ADUs on most single-family lots, with relaxed setbacks and no owner-occupancy requirement in many cases. Maximum size is typically 1,100 square feet or 0.15 FAR, whichever is less. Short-term rental rules apply if you plan to list on Airbnb.
Houston
Houston has no formal zoning, which makes ADUs surprisingly accessible. Deed restrictions in your subdivision are the real gatekeeper — check those before you spend a dime on plans. Permits go through the city, and detached ADUs must meet standard residential building codes.
Dallas and Fort Worth
Both cities permit ADUs, but with more restrictions than Austin. Dallas requires owner-occupancy on the primary lot and limits ADU size based on the main house. Fort Worth has similar rules and tends to be stricter on detached units in older neighborhoods.
San Antonio
San Antonio allows ADUs in most residential zones, often up to 800 square feet or 40% of the main home’s size. The city has actively encouraged ADUs as part of its affordable housing strategy.
Smaller Cities and Unincorporated Areas
If you’re outside a major metro, expect to deal with county rules, septic requirements, and sometimes HOA covenants that flatly prohibit secondary units. Always pull your deed restrictions first.
What Does an ADU Cost in Texas?
Costs vary wildly depending on size, finish level, site conditions, and your city’s permit fees. Here are realistic 2025 ranges:
- Garage conversion: $60,000 – $130,000
- Attached addition ADU: $150,000 – $300,000
- Detached backyard cottage (400–800 sq ft): $180,000 – $350,000
- Larger detached ADU (800–1,100 sq ft): $250,000 – $450,000+
On a per-square-foot basis, most Texas ADUs land between $300 and $500/sq ft — often more than a kitchen or bathroom remodel because you’re building an entire small home from scratch, including foundation, roof, HVAC, plumbing, and electrical.
Hidden Costs to Budget For
- Utility connections — separate water, sewer, and electric service can add $10,000–$30,000
- Impact fees — some cities charge $3,000–$8,000 for new dwelling units
- Survey and engineering — $2,000–$6,000
- Foundation work — Texas clay soils can push costs up, especially if you have any existing foundation issues
- HVAC — a properly sized mini-split or small system for an ADU runs $6,000–$12,000 (see our HVAC replacement guide for context)
Timeline: From Idea to Move-In
Plan on 9 to 14 months for a detached ADU, broken down roughly like this:
- Design and engineering: 6–10 weeks
- Permitting: 6–16 weeks (Austin and Dallas are slower right now)
- Site prep and foundation: 3–5 weeks
- Framing through finish: 4–6 months
Garage conversions are faster — usually 4 to 7 months total — because the shell already exists.
How to Find the Right ADU Contractor
Not every general contractor is set up to build ADUs. You want someone who has actually delivered finished units in your city and understands the local permit process. Here’s how to vet them.
Ask for ADU-Specific References
Don’t settle for “we’ve built additions.” Ask for three completed ADUs in the last two years, ideally in your city. Call those homeowners. Ask about timeline, surprises, and how the builder handled change orders.
Verify Licensing and Insurance
Texas doesn’t license general contractors at the state level, but trades like plumbing, electrical, and HVAC are licensed. Your ADU contractor should carry general liability (at least $1M) and workers’ comp, and should pull all permits in their name — not yours. Our guide on how to hire a contractor in Texas walks through the full vetting checklist.
Get Detailed, Line-Item Bids
A real ADU bid is 8–15 pages, not one. It should break down site work, foundation, framing, MEP (mechanical, electrical, plumbing), finishes, and allowances for items like cabinets and flooring. Vague bids are how budgets blow up.
Understand the Payment Schedule
Avoid contractors who want more than 10% upfront. A health