ADU size and setback standards depend on which approval pathway your property follows — and that depends on ADU Overlay status. The Dallas City Council approved a framework for ADU construction and rental in 2018, but unlike Austin’s by-right approach in many residential zones, Dallas requires clearing additional approval steps. Properties within an established ADU Overlay follow the setback rules written into that specific overlay — rules that were negotiated between the city and the neighborhood’s planning committee, and which can differ meaningfully from one overlay to the next. Properties not within an ADU Overlay go through a city action process, where setbacks and size limits are determined during that approval and often align with standard single-family or duplex zoning requirements rather than overlay-specific figures. The size limit commonly cited — 1,000 square feet or 30% of the primary dwelling’s floor area, whichever is less — applies in some contexts; an 800 square foot cap applies in others. Which figure governs depends on the pathway, and the pathway depends on whether the specific parcel sits inside an ADU Overlay. This is the single detail most likely to produce a mismatch between what a homeowner researched online and what their specific property is actually subject to.

PD districts and Conservation Districts override base zoning entirely — and Dallas has a lot of them. Many Dallas neighborhoods are governed by Planned Development (PD) districts or Conservation Districts (CD), each with custom standards for setbacks, height, lot coverage, and architectural requirements that supersede the citywide base zoning code. A site plan drafted from Dallas’s general residential zoning standards — without checking whether the specific parcel falls within a PD or CD — may apply setback figures that simply don’t govern that property. The Dallas GIS Interactive Map identifies PD and CD status, zoning district, floodplain designation, and historic district status by address, and checking it is the first step for any Dallas parcel, not an optional refinement.

Garage setback from an alley depends on which direction the garage faces. The standard accessory structure setback in Dallas is 5 feet from any other building on the same lot and 5 feet from an alley line. But when the entrance to an accessory building — typically a garage — faces the alley for automobile access, that structure must be set back at least 20 feet from the alley line, not 5. This is a fourfold difference triggered entirely by which direction the garage door faces, and it’s a detail that’s easy to miss when a site plan is drawn without specifying door orientation relative to the alley.

The Trinity River Corridor has its own permit — separate from standard floodplain development permits. Article V of the Dallas City Code establishes the Trinity River Corridor — the floodplain of the West Fork, Elm Fork, and mainstem segments of the Trinity River within Dallas city limits, as delineated on the Corridor Development Certificate (CDC) Regulatory Map. Any floodplain alteration within this corridor — construction, grading, filling, excavation — requires a Corridor Development Certificate from the Director of Water Utilities, in addition to whatever standard floodplain compliance otherwise applies. For properties near the Trinity River specifically (as opposed to other Dallas waterways), this is an additional permit layer beyond the general Article V floodplain requirements that apply citywide.

Standard floodplain rules require 2 feet of freeboard above BFE, and substantial improvement triggers full compliance regardless of project type. Outside the Trinity River Corridor, Article V (Flood Damage Prevention) still applies citywide: flood zone verification against current FEMA maps and the city’s regulatory floodplain maps is required for all permits, new residential construction must be elevated at least 2 feet above Base Flood Elevation, no development is permitted within the regulatory floodway, and improvements exceeding 50% of the property’s market value trigger full floodplain compliance — meaning even a “small” remodel can trigger floodplain requirements if its cost crosses that 50% threshold relative to the property’s value.