Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Richardson ADU cost →Building an ADU in Richardson costs between $140,000-$350,000 for new construction, with per-square-foot costs averaging $250-$400. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $30,000-$100,000, while prefab/modular ADUs fall in between at $150,000-$300,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | 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). |
| Impact Fees | None found. The Master Fee Schedule (Appendix B, as amended through Ord. 4560, Oct. 13, 2025) lists no development impact fee for residential work; the only impact-related charges are traffic impact analysis reviews filed with a zoning request ($500 without modelling, $1,500 with). Water and sewer connection charges are billed per the schedule; confirm with Development Services |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Richardson, where we have them — free, no obligation.
Get Richardson builder quotes →Permit fees in Richardson are 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).. The review timeline is 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., with 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). Impact fees are None found. The Master Fee Schedule (Appendix B, as amended through Ord. 4560, Oct. 13, 2025) lists no development impact fee for residential work; the only impact-related charges are traffic impact analysis reviews filed with a zoning request ($500 without modelling, $1,500 with). Water and sewer connection charges are billed per the schedule; confirm with Development Services. Pre-approved plans: None. No city pre-approved plan library exists, and none would be usable while ADUs are not a permitted use.
| 1-Bedroom Rent | $1,450-$1,950/month |
| 2-Bedroom Rent | $1,850-$2,300/month |
| Annual Rental Income (est.) | $20,400/year |
| Payback Period (est.) | 12.0 years |
| Short-Term Rental | 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. |
| Overall ROI Estimate | 5-8% annual return (hypothetical: ADUs are not a permitted use in Richardson) |
A typical ADU in Richardson generates approximately $20,400 per year in rental income based on average 1-bedroom rents. At an average construction cost of $245,000, the estimated payback period is 12.0 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Richardson and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Richardson: $30,000-$100,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $150,000-$300,000.
3. Pre-approved plans — available in Richardson, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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