A detached ADU is a second, freestanding home on your lot. In the City of Dallas it is not allowed by right on most single-family lots, as of October 2026. You need either an ADU overlay covering your neighborhood or a special exception from the Board of Adjustment before a building permit.
How big can a detached ADU be in Dallas?
Under the rules Dallas adopted in 2018, an ADU in an overlay district can be at least 200 sq ft and no larger than 700 sq ft or 25 percent of the main house's floor area, whichever is greater. A special exception granted by the Board of Adjustment can carry conditions of its own. We confirm the limit for your lot before drawing a floor plan.
Does the owner need to live on site?
Yes, under the 2018 rules. The owner must live in either the main house or the ADU, and the approval comes with a deed restriction recording that requirement. See can I rent out my ADU in Dallas?
What about the suburbs?
- Plano allows backyard cottages on many single-family lots with a building permit. See ADUs in Plano.
- Garland has a code section for ADUs, with size tied to the main house. See ADUs in Garland.
- Richardson zoning does not list a second dwelling as a permitted use. See ADUs in Richardson.
- Irving depends on your zoning district. See ADUs in Irving.
What drives the cost of a detached ADU?
- Foundation. North Texas clay soils call for engineered slab design.
- Utilities. The sewer run to the back of the lot and whether the electrical panel can carry a second home.
- Access. Alley access makes deliveries and equipment easier.
- Approval. A Board of Adjustment filing adds a fee, notice signs and a hearing.