Grand Prairie, TX Accessory Structures: ADU Rules (2026)

Article 30, Section 2 of the Unified Development Code defines an "Accessory Apartment" as a second dwelling unit, attached to or inside an existing single-family home or built as a separate accessory structure on the same lot, used as a complete independent living facility with its own cooking, eating, sanitation and sleeping provisions. Because it is classified as accessory to the main dwelling, the code cross-references the two-family/duplex use charts in Article 4 and imposes eight numbered conditions before the unit is allowed. The unit must have "a minimum size of 400 square feet covering no more than 35 percent of the original unit's total floor area," capping how large a garage apartment or basement unit can be relative to the primary house.

It is limited to "a maximum of two bedrooms," and must have a well-marked entrance so emergency responders and mail carriers can find it. The owner must certify adequate water and sewer service is available to the unit, and the property must provide one parking space for each adult resident of the accessory apartment, on top of parking for the main house. Street-facing appearance is controlled too: the code allows "no external evidence of the accessory apartment in the front of the structure, with the exception of an entrance," so a converted garage apartment cannot visibly announce itself from the street.

Occupancy is capped at four people in the unit. These standards apply citywide wherever an accessory apartment is a permitted accessory use; a homeowner adding one must satisfy every listed criterion, not just some, since the definition frames them as mandatory conditions on the use rather than optional design suggestions.