Everything homeowners ask about building an ADU in Richardson — answered with 2026 data.
No — under current zoning Richardson does not allow ADUs. Richardson's Comprehensive Zoning Ordinance of 1956, codified through Ord. No. 4590 (June 15, 2026) with nothing in the ten ordinances adopted since, lists no accessory dwelling unit, garage apartment or guest house as a permitted use in any residential district, and Art. II, Sec. 3 closes the use lists. The one accessory living space it recognises, Servants' quarters, is by definition not rented, not a separate dwelling, and may not have kitchen facilities or separate utility connections (Art. I, Sec. 2). Council began a zoning-ordinance modernisation in February 2026; no ADU text has been published. Details: None. No residential district lists an accessory dwelling unit, garage apartment or guest house, and Art. II, Sec. 3 closes every use list. In R-1500-M (Art. IV, Sec. 1) and R-1100-M (Art. VII, Sec. 1) the uses are single-family detached dwellings; accessory buildings (detached garage, carport, other); church; construction field office; farming; gardening; home-based business; home occupation; public building; rental rooms (max two renters); servants' quarters; parochial school; antennas. See our full Richardson ADU rules page for the narrow exceptions and what may change.
ADU construction in Richardson typically costs $140,000-$350,000. The cost per square foot averages $250-$400. Garage conversions are more affordable at $30,000-$100,000, while prefab ADUs cost $150,000-$300,000. Permit fees add Accessory building permit: $100 for a structure of 150 sq ft or less, $200 for one larger than 150 sq ft; a room addition is $200 up to 500 sq ft, then $200 plus $0.10/sq ft (Appendix B, Master Fee Schedule, Ord. 4559, Sept. 15, 2025). to your budget. See our detailed Richardson ADU cost guide.
Detached ADUs in Richardson can be up to N/A: a detached second dwelling is not a permitted use. Detached accessory buildings are capped instead: all detached structures together, garages included, may occupy no more than 8% of the lot area and may not exceed 40% of the floor area of the principal dwelling. Attached ADUs are limited to N/A: no attached ADU category exists. An addition is part of the principal dwelling and counts toward total lot coverage: 40% of the lot in R-1500-M. Junior ADUs (JADUs) have a cap of Not a category in Texas, and Richardson's ordinance has no junior ADU designation. Maximum height is N/A for ADUs. Accessory buildings are limited to one story: 12 ft for a building of 150 sq ft or less, 25 ft for anything larger (Art. IV, Sec. 3(b); Art. VII, Sec. 3(b)). The principal house may be two stories, first story 25 ft and second 15 ft (Sec. 3(a)). You are allowed up to 1 dwelling unit per lot. The residential districts permit "single-family detached dwellings" on a qualifying lot.
Rear setback: N/A for ADUs. The district rear setback is 25 ft, but a detached garage, carport or other accessory building may extend into it with a minimum 3 ft from the rear lot line, or 18 in where the rear lot line adjoins an alley (Art. IV, Sec. 4(g)(2); Art. VII, Sec. 4(g)(2)). Building Inspection measures these to the roof overhang. Side setback: N/A for ADUs. An accessory building must meet the principal building's side setback: 7 ft on a lot under 80 ft wide, 10 ft at 80 to under 120 ft, 15 ft at 120 ft or more, 20 ft on a corner lot beside a side street; within the required rear setback 3 ft is allowed (Art. IV, Sec. 4(f)(1), (f)(3)). Building Inspection's accessory-building sheet applies 5 ft for a building entirely within the rear 25 ft, or 3 ft with a UL-rated 1-hour fire wall both sides; confirm at 972-744-4180. Front setback: N/A for ADUs. The district front setback is 30 ft (up to 50 ft where an established building line governs), and no accessory structure may sit forward of it; unenclosed porches and similar appendages may project 5 ft (Art. IV, Sec. 4(e); Art. VII, Sec. 4(e)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
N/A for ADUs: no ADU standard exists. The residential baseline is two off-street spaces in an enclosed garage behind the front building line for each dwelling unit, attached or detached (Art. IV, Sec. 4(h)(1); Art. VII, Sec. 4(h)(1)). Converting a garage to living space requires a replacement detached garage of brick, stone or cementitious materials compatible with the house (Art. IV, Sec. 2(b)(2)), and any front-yard driveway must be removed or reconfigured (Sec. 4(h)(4)). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Moot for ADUs, since none may be built. Servants' quarters must be occupied by persons employed full-time on the premises as domestic help by the occupant, and may not be rented (Art. I, Sec. 2). Renting rooms inside the house is allowed to a maximum of two individual renters or tenants (Art. IV, Sec. 1(j); Art. VII, Sec. 1(j)). Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Richardson is typically Not published. Building Inspection (972-744-4180) posts no review time for accessory-building permits, and no ADU timeline exists because no ADU use exists. Plan check: Scaled drawings are required for any accessory building over 150 sq ft, and each exterior wall of a building over 150 sq ft must be at least 35% masonry (Art. IV, Sec. 2(b)(2)); 150 sq ft or less may be wood or metal. The building must be permanently anchored, and the approved permit must be posted on site before work starts. Richardson has adopted the 2021 International Codes and the 2020 National Electrical Code, and every contractor must be registered with the city ($100, Sec. 6-116). Pre-approved plans availability: None. No city pre-approved plan library exists, and none would be usable while ADUs are not a permitted use.
Average ADU rental income in Richardson: 1-bedroom units rent for $1,450-$1,950/month, 2-bedroom units for $1,850-$2,300/month. Short-term rentals: Moot for an ADU, but the house is regulated: any rental under 30 days, even a room, needs registration (Ch. 6, Art. XIII). Ord. 4597 (Aug. 10, 2026): no new single-family STR within 500 ft of a registered one; $300/yr. Expected ROI: 5-8% annual return (hypothetical: ADUs are not a permitted use in Richardson).
The minimum lot size for an ADU in Richardson is N/A for ADUs. District minimums for the lot itself: 9,000 sq ft, 72 ft wide and 125 ft deep in R-1500-M (Art. IV, Sec. 4(a)-(c)); 8,000 sq ft and 64 ft wide in R-1100-M (Art. VII, Sec. 4(a)-(b)). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Richardson, a garage conversion typically costs $30,000-$100,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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