Compare ADU zoning rules across 3 Colorado cities. Average ADU score: 7.7/10.
Gathered from the 3 cities 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 3 Colorado cities covered here, taken from each city's own ordinance rather than a state summary.
| Question | Across Colorado |
|---|---|
| Are ADUs permitted? | 3 of 3 permit them. |
| Detached size cap | Median 800 sq ft, from 750 to 864 sq ft across the 3 cities publishing a numeric cap. |
| Owner-occupancy | Required in none of them. |
| Build cost | $185,000 to $450,000 depending on city and unit type. |
| Easiest and hardest here | Boulder scores 8/10; Colorado Springs scores 7/10. |
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 |
|---|---|---|---|---|---|---|
| Boulder | 800 sq ft of floor area (BRC 9-6-3(n), Table 6-3); 1,000 sq ft for an affordable ADU (rent capped at 75% of area median income under a recorded declaration of use) or on a designated historic property. Floor area is measured to the outside of the exterior walls per Ch. 9-16 and includes stairways; space under a 6 ft ceiling is excluded. | Detached ADU (an accessory building) in RL-1, RL-2, RM-1, RM-2, RMX-1, RE and RR: 0 or 3 ft from the rear lot line (Table 7-1; a 0 ft setback needs a maintenance easement recorded with the neighbor unless the lot backs an alley or street), and 6 ft from any other building. Attached ADU: the principal rear setback can drop to 5 ft where only ADU floor area sits in the setback, that part is no taller than 20 ft and, in RR/RE/RL/RMX-1, covers no more than 500 sq ft (9-6-3(n)(2)(B), Ord. 8650). | Valuation-based (2026 schedule): $1,059 + $5.95 per $1,000 over $100,000, plus 25% plan check and $83.90 energy fee: about $1,700 for an 800 sq ft unit at the city's $170.80/sq ft floor, about $2,900 on a $300,000 contract. Use tax, trade permits, impact fees and excise tax are extra. | $200,000-$450,000 | $1,900-$2,400/mo | 8/10 |
| Colorado Springs | 50% of the principal dwelling's floor area or 1,250 sq ft, whichever is less; if the principal dwelling is under 1,500 sq ft the ADU may be 750 sq ft. ADU floor area does not count toward the lot's accessory-structure floor-area cap (7.3.304.E.2.a). | 5 ft for a detached ADU. The code caps the rear setback at the lesser of the district's accessory-building rear setback or 5 ft, so the City cannot require more (7.3.304.E.2.c(2)). | PPRBD permit is valuation-based ($45.65 per sq ft in 2025-26): about $345 for a 750 sq ft unit or $505 for 1,250 sq ft, plus a 28% plan-examination fee. City DRE plan review $180 (new structure) or $130 (addition) plus $25 IT fee (Res. 191-25, eff. Jan 1, 2026). No separate land-use application fee. | $185,000-$420,000 | $1,350-$1,800/mo | 7/10 |
| Denver | SU districts: ADU gross floor area 864 sq ft on lots of 7,000 sq ft or less, 1,000 sq ft on larger lots (DZC 11.8.2.1.B.2); the detached ADU building footprint is capped at the same 864/1,000 sq ft (e.g., DZC 5.3.4.5.A). Other districts: 1,000 sq ft footprint per unit, GFA not separately capped. | U- districts: 5 ft, or 0 ft where an alley abuts the rear line and no garage door faces it. E-SU: 5 ft where an alley or street abuts the rear; otherwise 5 ft (1-story) or 12 ft (2-story). S-SU: 10 ft (1-story) or 20 ft (2-story). The detached ADU must sit in the rear 35% of lot depth (U-, E-) or rear 50% (S-) (DADU building form tables). | Building permit is valuation-based: $770 + $5.60 per $1,000 over $100,000 (about $1,330 at $200,000) plus a 50% plan-review fee; zoning permit $150 + $0.50 per $1,000; SUDP $425 application + $150 inspection; Denver Water ADU system development charge $2,170 (from Jul 1, 2026). | $200,000-$450,000 | $1,650-$2,000/mo | 8/10 |
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