Compare ADU zoning rules across 1 District of Columbia cities. Average ADU score: 7.0/10.
Gathered from the 1 city below, with the bill or ordinance each one names. Statewide measures are listed once with the cities they reached, rather than repeated for each.
Statewide law sets a floor; the numbers that decide your project are local. Here is the spread across the 1 District of Columbia city covered here, taken from each city's own ordinance rather than a state summary.
| Question | Across District of Columbia |
|---|---|
| Are ADUs permitted? | 1 of 1 permit them. |
| Detached size cap | Median 450 sq ft, from 450 to 450 sq ft across the 1 cities publishing a numeric cap. |
| Owner-occupancy | Required in 1 of 1. |
| Build cost | $150,000 to $550,000 depending on city and unit type. |
Recomputed whenever a city page changes, so this and the city pages below cannot disagree.
| City | Max Size | Setbacks | Permit Fees | Build Cost | 1BR Rent | Score |
|---|---|---|---|---|---|---|
| Washington | Accessory-building footprint: the greater of 650 sq ft or 30% of the required rear yard in R-1/R-2, 550 sq ft in R-3 and the RF zones (D §5003, E §5003; raised from 450 sq ft on 7/10/2026). It counts toward the 40% lot occupancy (60% for an R-3 row house, D §210.1), may hold one dwelling unit and no roof deck (U §253.8(e)). | Accessory building: at least 7.5 ft from the centerline of any alley, 3 ft from a rear lot line that does not abut an alley or street, and no more than 30% of the required rear yard may be occupied by accessory buildings (D §5004.1, as amended 7/10/2026). The house itself needs a 25 ft rear yard in R-1 and 20 ft in R-2/R-3 (D §207.1). | New construction: $0.03 per cu ft of building plus a 10% enhanced fee and a $0.002/sq ft Green Building Fee. Alterations such as a basement conversion: $30 + 2% of construction value plus 10%, and a 0.13% green fee; a 50% filing deposit is paid up front (DOB Building Permit Fee Schedule). | $150,000-$550,000 | $1,500-$3,300/mo | 7/10 |
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