Dallas County

Dallas County regulates construction in unincorporated areas through the Department of Unincorporated Area Services (DUAS), in partnership with the Dallas County Fire Marshal's Office and Public Works. Because the county has no zoning authority (see countyOrdinance), DUAS does not restrict whether an ADU may be built — it regulates only subdivision/plat compliance, residential building-code inspection, on-site sewage (OSSF) compliance, floodplain compliance, 911 addressing, and nuisance abatement. A detached secondary dwelling on an unincorporated parcel is permitted as an ordinary residential structure through DUAS's building-permit pathway; there is no separate 'ADU permit' because there is no county use category for accessory dwellings. Unincorporated Dallas County comprises under 10% of county land area, primarily in the southeastern corner of the county. Most ADU activity in Dallas County occurs in incorporated cities (notably the City of Dallas ADU Overlay at Dallas Development Code Sec. 51A-4.510), which are governed by city-level permitting, not this section.

Process overview: Typical workflow for a new accessory residential structure on an unincorporated Dallas County parcel: (1) confirm parcel is in unincorporated Dallas County (not inside any city or city ETJ with extra-territorial platting authority) using the DUAS unincorporated-area map; (2) submit via MGO Connect with complete application, authorization form, property deed, recorded plat, site plan, survey, scope-of-work description, and fees; (3) plan review by DUAS Residential Building Inspection and the Fire Marshal's Office; (4) OSSF review if not on public sewer (a new dwelling on a septic lot requires a separate OSSF permit under Texas Commission on Environmental Quality rules implemented locally); (5) floodplain review if within a mapped Special Flood Hazard Area per FEMA FIRM effective 2019-03-21; (6) 911 address assignment via Public Works; (7) permit issuance, construction, inspections, final approval.

Impact fees: Dallas County does not levy municipal-style impact fees on residential construction in unincorporated areas; there is no county school, park, or traffic impact fee schedule because the county does not operate schools or parks at the county level in the way Texas municipalities or Texas school districts do. Fees are permit-processing fees only. Applicants should confirm the exact fee at intake since DUAS does not publish a single flat fee schedule on the public-facing page.

Dallas County itself does not appraise real property. Under Texas Tax Code Chapter 6, property-tax appraisal is performed by a single countywide central appraisal district. For Dallas County, that body is the Dallas Central Appraisal District (DCAD), a political subdivision of the State of Texas serving 61 local governing bodies inside Dallas County (the county, incorporated cities, school districts, hospital district, community college district, and special districts). The Dallas County Tax Office handles collection but not appraisal. An ADU is assessed as an improvement to the host parcel: DCAD adds the ADU's appraised value to the parcel's total improvement value on the next revaluation cycle and the homestead cap under Texas Tax Code Sec. 23.23 (10% annual cap on homestead appraisal increases) applies to the parcel as a whole if the parcel carries a residence homestead exemption. Texas does not permit splitting a tax parcel to separately tax an attached ADU, and unlike condominium sale of ADUs available in some states, Texas has no statewide ADU-condominium statute; each municipality that allows ADU sale must do so through its own zoning mechanism.

Assessment policy: Texas property appraisal runs on an annual cycle (Tax Code Ch. 25). DCAD values all real property at market value as of January 1 each year. An ADU completed between January 2 and January 1 of the following year is captured on the next appraisal cycle. The homestead-cap under Tax Code Sec. 23.23 limits the annual increase in appraised value of a residence homestead to 10% (excluding new improvements), so the ADU's value is typically added on top of the capped primary-dwelling value in its first appraisal year and then becomes part of the capped base going forward. There is no statewide ADU-specific exemption. Owners who disagree with the appraisal file a Notice of Protest with the Appraisal Review Board by May 15 (or within 30 days of the Notice of Appraised Value, whichever is later).

Dallas County's county-level overlays apply only inside its small unincorporated footprint (under 10% of county land, primarily southeastern Dallas County). The two material overlays at county scope are FEMA-mapped Special Flood Hazard Areas administered by Dallas County Public Works under the county's floodplain ordinance, and the countywide Trinity Common Vision Program governing floodplain management along the Trinity River corridor. Inside incorporated cities — where the vast majority of Dallas County residents and ADU-candidate parcels sit — overlay administration is a city function (e.g., the City of Dallas administers its own Escarpment Zone at Dallas Development Code Art. V and its own Floodplain regulations at Div. 51A-5.100). There is no countywide WUI / wildland-fire hazard overlay of the kind seen in California or Washington; North Texas's fire-hazard regime is ESD-by-ESD rather than a county-administered WUI zone.

• Dallas County Floodplain Management (FEMA NFIP participation) — A new ADU in a Zone AE parcel must be elevated to or above the Base Flood Elevation per the county ordinance and is generally not permitted as a basement or ground-floor sleeping space.
• Trinity Common Vision Program — Structures including ADUs proposed within the Common Vision corridor face stricter review than FEMA NFIP alone and may require a No-Rise Certificate from a Texas-licensed engineer.
• On-Site Sewage Facility (OSSF) jurisdiction — An ADU counts as an additional dwelling for OSSF sizing purposes, which can trigger system expansion on undersized lots and may be infeasible on very small unincorporated parcels.