ADU rules in Brownsville

The UDC's Permitted Use Chart lists Dwelling, Accessory as a use that may be attached or detached, permitted by right ('P') in the AG, RE, R-1, R-2, R-3, TN, TN-MU, TN-C, DE, DG, and DC districts; blank cells mean it is prohibited in CC, RC, LI, HI, and MOD. The RE and R-1 district descriptions expressly say those districts accommodate accessory dwellings. Only one ADU is allowed per lot, and a detached ADU must meet the setbacks of the principal dwelling, not the reduced accessory-building setbacks.

The chart definition of Dwelling, Accessory explicitly covers units attached to the primary structure, under the same by-right district permissions as detached units. Article 6 defines an ADU as an independent dwelling unit operated concurrently with a primary dwelling, so an attached ADU is a full separate dwelling, not just a spare room. The same one-per-lot, occupancy, and 50 percent size standards apply regardless of form.

The only size limit is relative, so a larger house allows a larger ADU. District lot-coverage maximums count all accessory buildings (50 percent total coverage in R-1, 60 percent in R-2, 40 percent in RE, 30 percent in AG), which can constrain a detached unit on a small lot. The ADU must meet the setbacks established for the principal dwelling.

The ADU standards, read in full, impose no requirement that the owner live in either unit, and a search of UDC Articles 1 through 6 found no owner-occupancy language for ADUs; the code instead states outright that ADUs may be rented. The one exception is short-term rental use: to operate an ADU as a rental of under 30 days, the STR ordinance's accessory-dwelling category requires the legal owner to reside on the property. Long-term rental of an ADU carries no owner-occupancy condition in the text.

The Permitted Use Chart assigns Dwelling, Accessory a ratio of 1 space per dwelling unit, and §4.6.2 makes the chart ratios the minimum, summed across all uses on the lot, so a typical house-plus-ADU lot needs 3 spaces. Residential parking areas and driveways must be concrete, and spaces generally cannot sit in the front setback in R districts.

ADUs are a by-right ('P') use in every district where they are allowed at all; no Specific Use Permit or other discretionary zoning approval attaches to them anywhere in the chart. The P entries cross-reference the additional use standards (one per lot, size, setbacks), which are objective conditions, not a hearing process. Construction still requires a standard building permit under §4.2.8.

The UDC states outright that ADUs may be rented. Since November 2024, renting any dwelling, including an ADU, for under 30 days is unlawful without a city STR registration and permit, a 24-hour local contact, the permit number on all listings, and hotel occupancy tax registration; violations are Class C misdemeanors with graduated fines up to $500 per day.