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 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). Details: None. No residential district in Richardson's Comprehensive Zoning Ordinance of 1956 lists an accessory dwelling unit, garage apartment or guest house among its permitted uses, and the lists are closed by Art. II, Sec. 3. In R-1500-M and R-1100-M — and in the same form across the R-2000-M through R-850-F districts — the permitted uses are single-family detached dwellings, accessory buildings (detached garage, carport, other accessory buildings), church, construction field office, farming, gardening, home-based business (no-impact), home occupation, public building, "rental rooms in a single-family dwelling, maximum of two individual renters or tenants," servants' quarters, parochial school on a church lot, antennas and rainwater harvesting (Art. IV, Sec. 1; Art. VII, Sec. 1). See our full Richardson ADU rules page for the narrow exceptions and what may change.
ADU construction in Richardson typically costs $120,000-$240,000. The cost per square foot averages $140-$265. Garage conversions are more affordable at $55,000-$140,000, while prefab ADUs cost $85,000-$190,000. Permit fees add Confirm with Richardson Building Inspection (972-744-4180) — the accessory building permit fee schedule is not published on the accessory building page 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. A detached accessory building is 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 residence. Attached ADUs are limited to N/A — no attached ADU category. An addition is simply part of the principal dwelling and is bound by the district's 30%-40% total building lot coverage. Junior ADUs (JADUs) have a cap of Not a category in Texas — Richardson's ordinance has no junior ADU designation. Maximum height is N/A for ADUs. Accessory buildings are limited to one story: 12 feet for a building of 150 sq ft or less, 25 feet for anything larger (Art. IV, Sec. 3(b); Art. VII, Sec. 3(b)). You are allowed up to 1 dwelling unit per lot. Richardson's residential districts permit "single-family detached dwellings" and nothing that would add a second unit; a duplex requires D-1400-M, D-2400-M or D-3000-M zoning, and anything else requires a PD planned development district with its own enumerated uses on a qualifying lot.
Rear setback: N/A for ADUs. For an accessory building, the district rear setback is 25 feet, but a detached garage, carport or other accessory building may extend into the rear setback with a minimum 3 feet from the rear lot line, or 18 inches where the rear lot line adjoins an alley (Art. IV, Sec. 4(g)(2); Art. VII, Sec. 4(g)(2)). Side setback: N/A for ADUs. An accessory building must meet the principal building's side setback — 7 feet on a lot under 80 feet wide, 10 feet at 80 to under 120 feet, 15 feet at 120 feet or more, and 20 feet on a corner lot adjacent to a side street — except that within the required rear setback a 3-foot side setback is allowed (Art. IV, Sec. 4(f); Art. VII, Sec. 4(f)). Note that the city's Building Inspection accessory-building page states 5 feet from the side property line for a building entirely within the designated rear yard, reducible to 3 feet with a UL-rated 1-hour firewall on both sides — check which figure your plan reviewer will apply with Building Inspection at 972-744-4180. Front setback: N/A for ADUs. The district front setback is 30 feet, and no accessory structure may sit forward of it (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)). Enclosing or converting a garage triggers a requirement to replace it with a detached garage built of brick, stone or cementitious materials architecturally compatible with the house (Art. IV, Sec. 2(b)(2)). 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 of the premises, 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)). 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 Confirm with Richardson Building Inspection (972-744-4180) — no published review timeline was found in a city source, and no ADU timeline exists. Plan check: Scaled drawings are required for any accessory building over 150 sq ft, and each exterior wall of an accessory building over 150 sq ft must be at least 35 percent masonry (Art. IV, Sec. 2(b)(2)). Richardson has adopted the 2021 International Codes and the 2020 National Electrical Code. All contractors must be registered with the city before work starts. 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 $1,150-$1,500/month, 2-bedroom units for $1,500-$1,950/month. Short-term rentals: Moot for an ADU, since none may lawfully exist — but Richardson does regulate short-term rentals of the house itself. Registration is required for any residential property rented wholly or partly for under 30 consecutive days, including a room within the house. Ordinance 4597, passed August 10, 2026, added a 500-foot separation requirement between single-family short-term rentals and raised the annual registration fee from $100 to $300; a property within 500 feet of a registered STR is ineligible. Hotel Occupancy Tax is remitted directly to the city through the registration system from October 1, 2026. Renting for 30 days or more instead requires long-term single-family rental registration. 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 are 9,000 sq ft in R-1500-M and 8,000 sq ft in R-1100-M, with minimum lot widths of 72 and 64 feet (Art. IV, Sec. 4(a)-(b); 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 $55,000-$140,000. 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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