Brownsville | ADUs and Duplexes

Brownsville Accessory Dwelling Units and Duplexes: Size, Districts and Parking

An accessory dwelling unit (ADU) is a second, smaller home on the same lot as a house, such as a garage apartment or a backyard cottage. A duplex is one building with two homes. Brownsville allows the first in most residential districts and the second in R-2, R-3 and four traditional districts. Texas has no statewide ADU law, so the City's Unified Development Code (UDC) sets every rule on this page. The Brownsville overview has the short version.

What the Code Calls an Accessory Dwelling Unit

Article 6 defines an accessory dwelling unit as "An independent dwelling unit on a lot zoned for Single-Family Residential operated concurrently with a primary dwelling unit." The Permitted Use Chart lists the same use as "Dwelling, Accessory" and describes it as "A dwelling unit that is attached or detached from the primary on-site structure, is used as a residence, is incidental to the main structure." So the unit may be inside or joined to the house, or a separate building in the yard.

In the traditional and downtown districts, Section 4.5.4 adds a building type for it. An "Accessory Building" is "A small self-contained structure located on the same lot as a detached house but physically separated. It may be used as a complete, independent living facility, with provisions for cooking, sanitation and sleeping or for a residential garage or for both." Section 4.5.3 says each lot has one building type, plus one accessory building where the district allows it.

The Accessory Dwelling Unit Rules

Source: Brownsville UDC Section 4.4.4.A, item 25 and the Permitted Use Chart, Supplement 26.

The size cap works from the house. Section 4.4.4 says the unit "shall be limited in size to not more than 50% of the total floor area of the principal dwelling's living space." By VanPlex arithmetic, a house with 1,200 square feet of living space allows a unit of up to 600 square feet, and a house with 2,000 square feet allows up to 1,000. In the traditional districts the accessory building type also sets a maximum depth of 28 feet, a maximum height of "2 Stories/30'," and a width no greater than the main building.

Setbacks are the distances a building must keep from the lot lines. The ADU rule says units "must meet the setbacks established for the principal dwelling." Under the June 2026 tables that means, in R-1, 10 feet from the front line, 5 feet from each side and 5 feet from the rear. The tables give a separate, smaller set of numbers for other accessory buildings, such as a shed or a detached garage: 10 feet from the main building, 5 feet from any other accessory building, and 5 feet from the side, rear and alley lines. For a unit people live in, follow the main house numbers.

The unit "may be rented or occupied by a guest," but "No more than one (1) household family unit" may live there at a time. Article 6 defines a household as people related by blood, marriage, adoption, fosterage or guardianship with "no more than 2 unrelated inhabitants," or a communal group of "no more than 8 inhabitants." The same definition refers to facilities "licensed by or contracted with the Oklahoma Department of Human Services," a reference that names another state's agency; ask the City how it reads that clause.

Which Districts Allow One, and a Numbering Problem

The use chart row for "Dwelling, Accessory" shows "P-24" in AG, R-1, R-2, R-3, TN, TN-MU, TN-C, DE, DG and DC, and "P-4" in RE. P means permitted by right, so the unit is allowed in all eleven. The MOD column and the commercial and industrial columns are blank. Each unit needs "1 : Dwelling unit," one parking space.

The numbers after the P are out of step with Section 4.4.4. The ADU standards are item 25 in that list; item 24 is the drive-thru rule and item 4 is the halfway house rule. The Article 6 definition also points to "Section 4.4.4A.24." The same shift shows on other accessory rows: carports read P-24 against item 23, and home occupations P-27 against item 28. The text of the standards is clear, so read the item titled "Dwelling, Accessory," and treat the RE cell as a permitted use with those same standards.

Duplexes

Ordinance No. 2026-235.127 added a new definition on June 16, 2026: a duplex is "A single principal building located on a single lot that contains exactly two dwelling units." The two units sit "side-by-side sharing one common wall, or stacked sharing a common floor/ceiling," and "each unit shall have a separate exterior entrance." The older chart definition, still printed on municode, describes two attached units "located on one or two lots." The June 2026 text is the later one. Two attached homes on two separate lots now fall under the townhouse definition, which the townhomes page covers.

The use chart allows a duplex by right in R-2, R-3, TN, TN-MU, TN-C and DE. In R-2 and R-3 the minimum lot is 2,000 square feet and 35 feet wide for a detached building, with a 0-foot side setback where fire separation rules are met, and a height of 35 feet in R-2 or 45 feet in R-3. In the Supplement 26 tables, R-2 also carried a cap of 22 homes per acre, which by VanPlex arithmetic needed 3,960 square feet for two homes. The June 2026 tables print no such cap, so confirm with the Planning Department whether any density limit still applies to your lot.

For R-1 and RE lots the path is a rezoning to R-2. The City made that change for a duplex on six sets of land between March and September 2026, including Ordinance No. 235-2026-004, which rezoned 0.87 acres at 1005 Robindale Road "TO ALLOW A DUPLEX AND ADU." The zoning districts page explains the hearings and the protest rules.

Parking changed in June 2026. Exhibit H of Ordinance No. 2026-235.127 sets "1 : Dwelling Unit" for the duplex, single-family and townhouse rows, where Supplement 26 shows "2 : Dwelling Unit." A duplex now needs two spaces in all. Each space must be at least "nine (9) feet wide by eighteen (18) feet deep," and residential parking areas and driveways "shall be concrete."

A Worked Example on an R-1 Lot

Take an R-1 lot at the district minimum of 50 by 100 feet, or 5,000 square feet, with a house of 1,600 square feet of living space. The numbers below are VanPlex arithmetic on the rules quoted on this page:

• The ADU may have up to 800 square feet, half of the house's living space.
• All buildings together may cover up to 3,500 square feet, the 70 percent coverage cap in the June 2026 table.
• The ADU keeps the house setbacks: 10 feet from the front line and 5 feet from each side and the rear.
• The lot needs two parking spaces: one for the house under the June 2026 chart and one for the ADU. Parking spaces stay out of the front setback; the table allows an exception for driveways and porte-cocheres, a roof over the drive at the door.
• A front garage or carport sits at least 25 feet from the front property line.

A wider R-1 lot changes the picture. Splitting a lot into two needs a plat, and each new lot must meet the R-1 minimums of 5,000 square feet, 50 feet of width and 70 feet of depth, or the small lot rule on a qualifying tract. The lot size page gives those numbers.

Permits, Design Credit and Fees

Section 4.2.4.C.2 says "Residential development that is platted and consists of three (3) or fewer units is exempt from the requirement to Site Plan and may apply for a building permit by submitting a Plot Plan." A site plan is a full drawing of buildings, parking, landscaping and drainage reviewed by staff. The plot plan is simpler: under Section 4.2.8 it shows property boundaries, easements, setbacks, "Proposed grading and drainage to the street," and the footprint, driveways, sidewalks and patios. The Building Official checks the application for completeness within ten business days and decides within thirty calendar days after it is complete.

Section 4.6.1.B offers a voluntary design score for houses and duplexes. At 60 points a project gains "an additional ten (10) feet of maximum height," ten percent more building coverage and a ten percent smaller minimum lot; at 80 points the gains are twenty feet, twenty percent and twenty-five percent. Points come from items such as clay tile or metal roofs (10 points) and a rainwater system that holds at least 1,000 gallons (15 points).

Source: Exhibit A, FY 2027 Master Fee Schedule (Ordinance No. 2026-1761-B), Planning and Redevelopment Services rows, in the agenda packet of September 22, 2026.

One plat rule needs a check before you design. Brownsville applies the state's Model Subdivision Rules to plats that create two or more lots of five acres or less for homes, and Section 3.1.6.J requires those plats to carry the note "No more than one single family detached dwelling shall be located on each lot." The note is written on the plat and in deeds, and it sits beside zoning that allows a duplex or an ADU. Read the recorded plat for your lot and ask the Planning Department how it applies the note to a second unit.

Where to Go Next

Related on VanPlex: the Brownsville overview, ADUs in Texas and building codes from duplex to fourplex.

Frequently Asked Questions

Official sources (checked October 2026)