Houston | Second Units and Duplexes

Houston Second Units and Duplexes: Two Homes on a Single-Family Lot

Houston has no zoning map, so the question "is my lot single-family?" is answered by one definition in Chapter 42 of the City code and by the deed restrictions recorded on the subdivision. That definition allows two homes on a lot in two forms: a duplex, or a house with a detached second dwelling unit of up to 1,500 square feet. This page sets out the definition, the parking each home needs, and the driveway rules for narrow lots. The Houston overview gives the short version.

What Sec. 42-1 Counts as Single-Family

Sec. 42-1 defines "single-family residential" in three sentences. The first covers "a lot with one building designed for and containing not more than two separate" units. The second says: "A lot upon which is located a free-standing building containing one dwelling unit and a detached second dwelling unit of not more than 1500 square feet shall also be considered single-family residential." The third covers attached homes on their own lots: a building with one dwelling unit that is "connected by a party wall to another building containing one dwelling unit on an adjacent lot." A party wall is a wall shared by two buildings on the line between two lots.

The same section defines a dwelling unit as a structure, or part of one, with "independent living facilities including provisions for nontransient sleeping, cooking and sanitation." In plain words, a dwelling unit is a home with its own place to sleep, cook and wash.

Source: Houston Code of Ordinances, Sec. 42-1, as amended by Ord. No. 2023-801, effective November 27, 2023.

Two results follow from the table. A third home on the lot moves the project out of the single-family definition and into the rules on the three to eight units page. A detached second building larger than 1,500 square feet is outside the second sentence of the definition, so ask the Planning and Development Department how it classifies that layout before you draw it.

The Detached Second Dwelling Unit

The City's Livable Places user guide describes a second dwelling unit as "a detached unit allowed on a single-family residential lot" that is "typically located above a garage or within a separate structure from the first unit, and cannot exceed 1,500 square feet in size." The guide also uses the names accessory dwelling unit and ADU. The City's FAQ gives the garage apartment as its example.

The size cap changed in 2023. The City's September 27, 2023 press release says the amendments increase "the maximum size of the second dwelling unit from 900 to 1,500 square feet" and require "parking based on the unit size." City Council adopted them as Ordinance No. 2023-801 for Chapter 42 and No. 2023-802 for Chapter 26, and both took effect on November 27, 2023. The release says they apply "to development and redevelopment inside the Houston city limits."

The user guide adds two practical points. "Where feasible, a SDU should take vehicular access from an alley." The Planning Department's ADU|HOU program offers a design book with 26 schematic designs, three videos, and a set of construction drawings that the guide says has preliminary approval from Houston Public Works. Existing homes are unaffected: the City's Livable Places FAQ says "Nothing affects the construction or remodel of an existing home, unless the lot is split into smaller lots."

Duplexes

A duplex is one building with two homes. The first sentence of the Sec. 42-1 definition covers it, and that sentence sets no size cap on either home. The 1,500 square foot cap applies to the detached second unit only. The FAQ states the City's position in one line: "the City's development code allows duplexes on a single-family lot. However, the City does not allow construction of a duplex if deed restrictions prohibit more than one dwelling unit on a lot."

A duplex lot follows the same lot rules as a house lot. Under Sec. 42-181 the lot must be at least 3,500 square feet inside the city and 5,000 square feet in the extraterritorial jurisdiction (ETJ), the unincorporated land outside the city limits where the City applies its plat rules. Smaller lots are possible inside the city under the standards on the lot size and small lots page. On such a plat the density cap counts homes. Sec. 42-184 limits "the number of single-family residential dwelling units that can be constructed" to 27 per gross acre, or 35 when every lot takes vehicle access from the rear or side. A gross acre counts all land inside the plat boundary. The user guide's Second Dwelling Unit Concept 6 shows a 5,000 square foot site split into two alley lots, each with a house and a second unit, and lists it at 35 homes per acre.

Two duplexes on one tract are four homes. Sec. 42-1 names "multiple duplexes" as a form of multi-unit residential, which has its own site standards in Sec. 42-237.

Parking for Two Homes

Parking is set in two places that say the same thing: Sec. 42-186 in Chapter 42 and the Class 2 rows of the table in Sec. 26-492. Off-street parking means parking on private land, outside the public street.

Source: Houston Code of Ordinances, Sec. 42-186(a) and (b) and Sec. 26-492, as amended by Ord. No. 2023-801 and 2023-802.

The three tests for the zero-space row are in Sec. 42-186(a)(2): the lot has less than 33 feet of public street frontage, the whole street side of the home is occupiable space (a term the City Construction Code defines), and driveway access from the public street is barred and shown on the plat and the building permit.

The user guide gives worked examples on a 50 by 100 foot lot. Its Second Dwelling Unit Concept 4 pairs a house of 1,600 square feet with a second unit of 1,000 square feet and provides two off-street spaces. The house needs two and the second unit adds none. The guide reads the first-unit condition this way: one more space is required "if the first unit does not meet the parking requirements," or if the second unit is between 1,001 and 1,500 square feet.

Two more parking rules from Chapter 26 affect a small site. Sec. 26-582(c) allows tandem parking, one car behind another, only when both spaces are reserved for the same home. Sec. 26-585 bars compact-car spaces in any building or tract designed for residential use. Sec. 26-472 defines a parking space as a marked area "wholly within private property that is all-weather surfaced."

Driveways on Narrow Lots

Sec. 42-1 defines a narrow lot as one with less than 44 feet of frontage on a street. Frontage is the length of the lot along the street. The driveway rules for such lots are in Sec. 42-188 and apply when land inside the city is subdivided. A property that touches an alley maintained by the City or a homeowners association must take vehicle access from the alley. In the middle of a block with no usable alley:

• a lot 44 feet wide or more must leave at least 20 feet of its frontage as open curb space;
• a lot 33 feet wide or more but under 44 feet, on a property of 15,000 square feet or less, may have one driveway from the street of no more than 12 feet;
• a narrower new lot must use a flag staff, a shared driveway or a permanent access easement.

A flag staff is the narrow strip that connects a rear lot to the street. A shared driveway is a private roadway that serves two or more lots. A permanent access easement is a privately owned and maintained street easement. Lots that were already under 33 feet wide before September 27, 2023 may have a direct driveway of no more than 12 feet when they meet all six standards in Sec. 42-188.5.

The FAQ explains when these rules apply: "these rules apply only when someone splits a residential lot into two or more lots to sell separately after the effective date of the ordinance." It also says a home on a lot at least 33 feet wide "can still have their own driveway from the street that can hold as many as four cars in the garage and driveway combined."

The front of the home is regulated too. Under Sec. 42-157(b), when the garage faces the street, at least one third of the structure along the street must be occupiable space with the front door facing the street. A narrow lot that cannot meet the one-third rule must provide a functional balcony on the second floor, or at least 36 square feet of windows facing the street with one window of 3 feet by 5 feet or more.

Building Lines for the Second Building

A building line is the required distance between a building and the street. For a lot restricted to single-family use on a local street, Sec. 42-156(b) sets 20 feet along the front and 10 feet along a back or side that adjoins a local street, or 10 feet when the plat shows a typical lot layout and the matching notes. Inside the city, Sec. 42-157(b) allows 10 feet for the main structure and 19 feet for a garage or carport that faces the street. Sec. 42-157(c) allows a 5-foot front building line when vehicles reach the lot only from the rear or side and each home on the street has a front door with an entry feature, such as a porch or stoop.

Deed restrictions can require more. Sec. 42-150(b) says: "Where deed restrictions provide for a greater building line or setback, the deed restrictions shall control over the provisions of this chapter." The parking and building lines page has the full table.

Deed Restrictions Decide First

Deed restrictions are private rules recorded with the county for a subdivision. The City's FAQ says: "The City has no authority to override or supersede active, private deed restrictions." It says the larger second dwelling unit is available if "your deed restrictions allow it."

The City also enforces these restrictions. Chapter 10, Article XV of the City code defines a restriction to include a limit that "affects the size of a lot or the size, type, and number of structures that may be built on the lot." Sec. 10-552(a) sets civil penalties of up to $1,000 per day for an owner who fails to comply after notice. Sec. 10-552(b) makes it unlawful to build under a permit when the work violates a recorded restriction and the applicant swore in a required affidavit that it complied. The deed restrictions page explains how to find and read them.

Flood rules apply to a new second building as new construction. In flood zones A, AE, AH, A99 and X Shaded, Sec. 19-33 requires the lowest floor and all utilities of a new home to be at or above the 500-year flood elevation plus 2 feet. See the flood rules page. For state law on accessory units, see ADUs in Texas.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)