Corpus Christi | ADUs and Duplexes

Corpus Christi ADUs and Duplexes: Size Caps, Owner Rules and Two-Family Lots

Corpus Christi gives a house lot two ways to reach a second home. The first is a detached accessory dwelling unit (ADU), a small second home on the same lot as a house, allowed in every residential district under Section 5.3.2.A of the Unified Development Code (UDC). The second is a two-family house, which the code also calls a duplex, allowed by right in RS-TF and the four RM districts. This page sets out the size, owner, meter and lot rules for each, and the narrow overlay route for a duplex in RS-6 or RS-4.5. The Corpus Christi overview gives the short version.

The Detached ADU Rule

Section 5.3.2.A is short, and each line matters. It says a detached ADU "may be permitted in any residential zoning district," that "the unit may include a full kitchen," and that "only one accessory dwelling unit shall be permitted per lot or parcel." Section 4.1.1 defines "residential zoning district" as every district under the "Residential Districts" heading of Table 4.1.1, which runs from FR to R-MH, so the rule covers the two-family and multifamily districts as well as the house districts.

The section then sets five limits:

• Owner on site: "The property owner shall occupy either the principal dwelling or the accessory dwelling unit."
• Size: the lesser of the main house's total gross floor area or the district cap in the table below.
• Coverage: the house and ADU together "shall not exceed the maximum zoning district building coverage."
• Yards and height: "All principal structure yard requirements shall be met," and the ADU may not exceed the district's height limit.
• Meters: "Separate meters are prohibited except for irrigation purposes."

The rule names only a detached unit. It says nothing about an ADU inside or attached to the house, so ask the Development Services Department how it treats one before you design it.

ADU Size by District

Source: Corpus Christi UDC, Section 5.3.2.A, items A to D, and Table 4.3.3. In every district the ADU may not exceed the main house's total gross floor area.

The garage rule is the largest opening. Item D says "an existing garage built prior to 1980 may convert to one accessory dwelling unit with no maximum on floor area if the garage is a legally conforming structure. The conversion can include an upper story Accessory Dwelling Unit over the garage." For such a garage on an RS-6 or RS-4.5 lot, the 500 square foot cap does not apply. The UDC does not define "legally conforming," so ask the City to confirm the garage's status, and its year of construction, before you design the unit.

Two Places Where the ADU Rules Disagree

First, the general accessory rule in Section 5.3.1 says detached accessory buildings "shall be located behind the front face of the main principal structure and the total square footage of all accessory buildings shall not exceed 50% of the main principal structure total square footage," or 75 percent in FR. Section 5.3.2.A allows an ADU up to the main house's full floor area within its district cap. On an RS-22 lot with a 1,600 square foot house, the ADU cap is 1,000 square feet under 5.3.2.A and 800 under the 50 percent rule, by VanPlex arithmetic. The code does not say which controls. A written interpretation from the City, listed at $665.50 in the FY 2026 fee schedule, settles it for one lot.

Second, the ADU rule caps the house and ADU at "the maximum zoning district building coverage," which Section 4.2.7 defines as the share of the lot covered by buildings. Table 4.3.3 for the house districts prints no building coverage limit; it sets a minimum open space of 30 percent in RS-22 to RS-4.5. Ask how the City applies the coverage line before you size an ADU.

Meters, Garages and Parking for an ADU

The one-meter rule appears twice. Section 5.3.2.A bars separate meters except for irrigation, and the Section 1.11 definition of dwelling says "single-family residential dwelling units shall only have one meter per utility; an additional meter shall be allowed only for agricultural/irrigation uses." For a rental ADU, that means the owner divides one water bill and one electric bill between two households.

Garages have their own limits in Section 5.3.2.D. A garage for a single-family residence "must not exceed 49% of the main building," a garage facing a street keeps the district street yard and never less than 20 feet, and a garage facing an alley is set back at least 3 feet. Section 5.3.1 adds that no accessory building may be built until work on the main structure has started.

Parking is less clear. Table 7.2.2.B has no row for an ADU. The household living rows require 1 or 2 spaces for a caretaker's quarters or upper-story unit, and "2 per unit" for "all other uses." Ask the City which row it applies to an ADU, because the answer sets how many spaces the lot needs in all.

Duplexes in RS-TF and the RM Districts

Section 4.4.4 defines a two-family house as "two attached dwelling units under single ownership, in a single structure and on a single lot (often called a duplex). The two units may be located on separate floors or side- by-side." Table 4.4.2 permits one by right in RS-TF, RM-1, RM-2, RM-3 and RM-AT. The RS-TF purpose statement adds that "a minimum of two-unit townhouse structures is permitted per platted property provided each townhouse unit is in compliance with the current Building Code," so two townhouses on their own lots are a second option there.

Source: Corpus Christi UDC, Table 4.4.3.A, two-family column, and Table 7.2.2.B.

The RS-TF numbers allow a taller and more open building than a house: 45 feet against 35 for a detached house in the same district, and 40 percent open space against 30. In the RM districts, Table 4.4.3.B sets a 6,000 square foot lot and 50 feet of width in RM-1 to RM-3, with 5-foot side yards for one- and two-family homes. In RM-AT a two-family lot needs 10,000 square feet and 85 feet of width, or 5,000 square feet and 50 feet on Padre Island, Mustang Island and North Beach.

The two-family rules in Sections 4.4.2 to 4.4.4 set no owner-occupancy rule. The owner rule in Section 6.14.5 applies to overlay duplexes on one lot, covered below. Yards, height and parking for a duplex are compared with other home types on the parking, setbacks and height page.

Duplexes in RS-6 and RS-4.5: the Overlay Route

Section 6.14, "Alternative Housing Options," lists vertical and horizontal duplexes among housing types that are permitted "within the following development concepts": the Mixed Use, Uptown-Downtown Mixed Use, Target Area Redevelopment, Clustered Development, Traditional Neighborhood and Transportation-Oriented Development overlays, and adaptive reuse projects in two of them. A development concept is a planned project with its own standards. Section 6.6 says a concept applies by right in the districts its standards list, and requires a rezoning where its densities could harm neighboring uses.

Section 6.14.5 then narrows the house districts: "Duplex and Live-Work units are only permitted in the RS-6 and RS-4.5 districts" when the duplex "is an infill project on a nonconforming lot," when it provides "a transitional density buffer" between a higher density use and a house, or when it is part of a listed development concept. The same section sets these terms:

• On a single lot, "the lot and both units within the duplex must be owned by the same owner, and the owner must reside within one of the two units."
• "A maximum density of one vertical or horizontal duplex dwelling unit per lot is permitted."
• "The conversion of an existing home to a horizontal duplex is prohibited" outside a neighborhood mixed use or live-work project.
• A front porch covering at least 50 percent of the front of one unit, matching materials, roof pitch and windows on both units, and no exterior stair on the front of the building.
• All parking and garages for a duplex on one lot must sit behind the units (Section 6.14.8).

Table 6.14.3.2, for neighborhood mixed use, marks one vertical duplex per lot in RS-4.5, RS-TF, RM-1 to RM-3 and several commercial districts. It also lists an "RS4" row, a district that Table 4.1.1 does not contain. Ask which district the City reads that row to mean.

Building Code, Modular Homes and Permit Fees

Section 14-291 of the Code of Ordinances adopts the 2021 International Residential Code, the building code for houses and duplexes, with City changes. In the City's text, section R313.2, which would require fire sprinklers in one- and two-family dwellings, is struck through, so a duplex or ADU needs none under the City code. Section R322 on flood-resistant construction "is deleted in its entirety" and replaced by the City's flood code.

A modular duplex or ADU is "industrialized housing" under Section 4.3.7. For single- and two-family homes it must have "a value equal to or greater than the median taxable value" of the single- and two-family homes within 500 feet, siding and roof pitch compatible with them, and a permanent foundation.

Fees are set in Section 14-1313 and printed in the FY 2026 schedule for October 1, 2025 to September 30, 2026: a residential building permit of $0.461 per square foot with a $146.41 minimum, plan review of $0.146 per square foot, and electrical, plumbing and mechanical permits of $0.075 per square foot each, all with a 4.5 percent administration surcharge. The code raises them each October 1 by a construction index, so ask for the current amount.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)