Fort Worth ADU Cost 2026: $120K–$240K for a Detached Build

A new detached ADU in Fort Worth typically costs $120,000–$240,000 all-in, with an 800 sq ft unit averaging $185,000–$240,000. Garage conversions run $55,000–$135,000. These are secondary-source estimates (aduzoning.org, local DFW builder data) — no official City of Fort Worth cost dataset exists, so treat these as planning ranges and get a site-specific bid.

Yes. Accessory dwelling units are permitted as an accessory use on one-family residential lots (zoning districts A-5, A-7.5, A-10, A-21, A-43, and AR) under Fort Worth Zoning Ordinance §5.301, "Accessory Uses on Residential Lots." A standard building permit is required — Fort Worth does not have a blanket by-right approval process, and lot-specific zoning should be confirmed with Development Services before you design.

Fort Worth's code does not publish one clean citywide square-footage cap the way Austin or Dallas do. The clearest rule in the ordinance: ADUs of 800 sq ft or less are exempt from floor-area-ratio, structure-coverage, and landscape-coverage calculations, which is why 800 sq ft is the size builders design toward by default. Height cannot exceed the primary residence, and non-habitable accessory structures are separately capped at 10–12 ft. Confirm your lot's exact allowance with Development Services (817-392-2222) before finalizing plans.

Fort Worth doesn't publish an ADU-specific permit-fee line item. Based on the general residential building-permit fee schedule, expect roughly $2,000–$8,000 in combined building permit, plan review, and impact fees for a typical detached ADU, plus separate water and sewer impact fees. Fort Worth's published water impact fee is $1,796 and sewer impact fee is $4,490 per unit (fee-schedule period through 12/31/26) — verify current amounts and get an address-specific estimate at the city's permitting portal (cfwpermit.fortworthtexas.gov) before budgeting.

This is genuinely unresolved from public sources. Fort Worth's ordinance bars an ADU from functioning as "a separate, independent residence," which several secondary sources read as an implied owner-occupancy requirement, while others state no such requirement exists in most zones. Because the answer directly affects whether you can rent out both units, confirm in writing with City of Fort Worth Development Services before you commit to a rental-income business plan.

Fort Worth has no published official turnaround-time page for ADU-specific reviews. Simple accessory-structure permits (sheds, small additions) commonly clear in 1–3 weeks; a full ADU requiring plan review across multiple trades more commonly takes 4–9 weeks from complete submittal to issuance, based on third-party permitting-guide estimates rather than a city SLA. Fort Worth ranked #1 of 500 U.S. cities in the 2025 Labrynth Red Tape Index for permitting speed and transparency, which is a real, independently reported signal that the city's process runs faster than most metros — but it is not a guaranteed timeline for your specific project.

Much of Tarrant County sits on expansive clay (Eagle Ford and Austin Chalk formations) that shrinks and swells with moisture, the same soil condition that drives up foundation costs across the Dallas–Fort Worth metroplex. A standard slab that might run $3,000–$12,000 for a 600 sq ft unit can require a post-tension slab or drilled piers instead, adding roughly $8,000–$25,000 depending on the geotechnical report's findings. Budget for a $500–$1,500 soil report before finalizing your foundation design.