ADU Ledger
ADU Ledger / Colorado
State hub · 12 cities

Colorado ADU rules, city by city

HB24-1152 (2024): HB24-1152 (codified at C.R.S. 29-35-401 through 29-35-405) required every Colorado city or town of 1,000+ residents inside a metropolitan planning organization to allow one ADU wherever a single-family home is allowed, through administrative approval, by June 30, 2025 — banning ongoing owner-occupancy mandates (an at-application residency check is allowed), most new-parking requirements, and design standards that would block an ADU in the 500–750 sq ft range. Note the contrast with Washington: one ADU per lot, not two.

Adoption on the Front Range has been messier than Washington’s: several cities complied early and generously, one got a state extension and adopted late, one saw voters repeal its entire new zoning code, and several still carry code that appears to conflict with the statute — including cities the state formally identified as non-compliant in October 2025. Where a city’s code conflicts with state law, the statute controls, but a homeowner still faces the city’s counter. Every value below cites the code as written, with compliance flags where it collides with C.R.S. 29-35-403.

Statewide questions

What is HB24-1152? · Which Colorado cities are not complying with the ADU law? · Does Colorado allow two ADUs per lot? · What happened to Lakewood's zoning code? · How big can an ADU be in Colorado? · What is the 500 to 750 square foot size protection in Colorado's ADU law? · Do Colorado cities require ADU owners to live on the property? · Can Colorado cities require parking for an ADU? · What does home rule mean for Colorado's ADU law? · What do Colorado ADU permits cost? · How long does it take to get an ADU permit approved in Colorado? · Can I rent out my Colorado ADU short-term on Airbnb?

Compare cities

RuleArvadaAuroraBoulder
ADUs allowed per lotOne ADU per lot with a single-family detached home, in residential, OT, and MX districts — either Type A (detached) or Type B (interior/attached with separate access), not both.LDC §5-1-5-2.A, .C, .GAs codified: one detached ADU per single-family home — attached and internal ADUs prohibited — and only in the Original Aurora MU-OA subdistricts (OA-R1, OA-R2, OA-RMU) on alley-served lots, plus the Painted Prairie master-planned area under its own development plan. State law requires far more; the code hasn't caught up.UDO §146-3.3.6.G.1; Table 3.2-1; contrast C.R.S. 29-35-403(1)One ADU per lot — attached or detached, not both — on a lot with one detached home, by right in all zoning districts except RH-6, MH, BMS, BCS, IS-1, and IM.B.R.C. 9-6-3(n)(1)(A)(i); 9-6-1 Table 6-1
Maximum sizeThe lesser of 40% of the home's living space and a lot-size tier: 600 sq ft on lots up to 6,000 sq ft; 850 up to 12,499; 1,000 up to an acre; 1,200 beyond. The 600 sq ft tier sits inside the 500–750 sq ft range state law protects — an apparent conflict. In-footprint conversions may reach 50% of the home including basement.LDC §5-1-5-2.E, Table 5-1-5-2; contrast C.R.S. 29-35-402(18)650 sq ft — below the 750 sq ft the statute protects, one of several provisions in apparent conflict with state law.UDO §146-3.3.6.G.1.h; contrast C.R.S. 29-35-402(18)Attached: the lesser of half the house's floor area or 1,000 sq ft (750 if the house is under 1,500). Detached: 800 sq ft. Affordable ADUs (rent capped at 75% AMI) and designated historic properties get more: attached to 1,200, detached to 1,000. Areas under 6-ft ceilings, mechanical rooms, and below-grade parking don't count.B.R.C. 9-6-3(n)(1)(A)(ii), Table 6-3
Detached ADU height25 ft in most RN subdistricts; 30 ft in RN-32.5, R6, R13, R24, and MX districts.LDC Table 2-1-3-3A (rows added by Ord 4905)No taller than the principal dwelling, and never more than 24 ft.UDO §146-3.3.6.G.1.i, .p20 ft for a detached ADU; the manager may allow 25 ft with a roof pitch of 8:12 or steeper. Conversions of legal existing accessory buildings may keep their height and roof form.B.R.C. 9-6-3(n)(3)(A)
Detached ADU setbacksPrincipal-dwelling standards: RN interior side 5–15 ft, rear 10–15 ft by subdistrict — and zero rear setback where the lot abuts an alley. A detached ADU must sit at or behind the house's front plane (10 ft behind the façade on both frontages of a corner lot).LDC §5-1-5-2.B, .F; Table 2-1-3-3ARear yard only; 5 ft side, 5 ft rear, 3 ft from the alley. An ADU atop an existing garage may keep the garage's setbacks.UDO §146-3.3.6.G.1.o; §146-4.2.3.F.1Accessory-building setbacks: interior side and rear 3 ft; front 55 ft or behind the house's rear wall; 6 ft of separation from any other building. An attached ADU can extend into the rear setback under conditions (ADU-only space, 5 ft off the rear line, ≤500 sq ft, ≤20 ft tall).B.R.C. 9-7-1 Table 7-1; 9-6-3(n)(2)(B)
Off-street parkingOne on-site space required for the ADU, in addition to the home's parking (tandem allowed) — broader than the narrow case where state law permits requiring a new space.LDC §5-1-5-2.D.1–2; contrast C.R.S. 29-35-403(3)One additional alley-accessed off-street space — and alley service is itself a prerequisite for the use. Both likely exceed what the statute permits.UDO §146-3.3.6.G.1.a, .k; contrast C.R.S. 29-35-403(2)(a), (3)None — the parking chapter contains no minimum vehicle-parking requirements for ADUs (or anything else; only maximums in two districts).B.R.C. 9-9-6
Owner-occupancyStill required, ongoing: the owner must occupy the house or the ADU, enforced by a recorded deed restriction that ties the ADU's certificate of occupancy to continued owner occupancy and bars separate sale. State law has barred ongoing owner-occupancy requirements since June 30, 2025; Arvada's August 2025 amendment left this in place.LDC §5-1-5-2.K, .L; contrast C.R.S. 29-35-403(2)(b)Still codified: the owner must occupy the primary dwelling or the ADU. Preempted on paper by state law since June 30, 2025, but not repealed.UDO §146-3.3.6.G.1.l; contrast C.R.S. 29-35-403(2)(b)Not required since March 8, 2025 — the city's page says so explicitly, and no owner-occupancy standard survives in the code.City ADU page; B.R.C. 9-6-3(n) (absence verified)
Lot coverage / floor areaDistrict standards apply (RN lot coverage 25–40% by subdistrict); in the OT district the ADU footprint is capped at the lesser of 800 sq ft or 40% of the house's footprint.LDC §5-1-5-2.B; Table 2-1-5-10BLot must exceed 6,000 sq ft; the ADU may cover no more than 50% of the rear yard, and 360 sq ft of usable private open space (minimum dimension 10 ft) must remain.UDO §146-3.3.6.G.1.e, .gThe lot must still meet district FAR and building-coverage limits, and accessory buildings between the house's rear setback and the rear lot line are capped at 500 sq ft of cumulative coverage in the RR/RE/RL/RMX-1 districts.B.R.C. 9-7-1 Table 7-1; 9-7-8(a)
Permit path & timelineAdministrative building permit via eTRAKiT, with a licensed contractor required. Published review timelines — rare and welcome: about 3 weeks for a detached (Type A), 1–2 weeks for an interior/attached (Type B).City ADU page; LDC §3-1-2-1.BConditional use with a Planning Commission public hearing — the opposite of the administrative approval state law mandates. No published timeline.UDO Table 3.2-1; contrast C.R.S. 29-35-403(1)Building permit only — the prior administrative-review step was eliminated in September 2023. ADUs in old PUD areas are approved as minor modifications, and prior PUD ADU bans are void. No published timeline.City ADU page; B.R.C. 9-6-3(n)(1)(A)(viii)

Every city, rule by rule

The full corpus, one rule at a time — how all 12 cities answer each question.

ADUs allowed per lot
  • ArvadaOne ADU per lot with a single-family detached home, in residential, OT, and MX districts — either Type A (detached) or Type B (interior/attached with separate access), not both.LDC §5-1-5-2.A, .C, .G
  • AuroraAs codified: one detached ADU per single-family home — attached and internal ADUs prohibited — and only in the Original Aurora MU-OA subdistricts (OA-R1, OA-R2, OA-RMU) on alley-served lots, plus the Painted Prairie master-planned area under its own development plan. State law requires far more; the code hasn't caught up.UDO §146-3.3.6.G.1; Table 3.2-1; contrast C.R.S. 29-35-403(1)
  • BoulderOne ADU per lot — attached or detached, not both — on a lot with one detached home, by right in all zoning districts except RH-6, MH, BMS, BCS, IS-1, and IM.B.R.C. 9-6-3(n)(1)(A)(i); 9-6-1 Table 6-1
  • Colorado SpringsOne ADU per lot with a single-family detached home — attached, integrated, or detached — in all districts where single-family homes are allowed. Wildfire (WUI-O) overlay: integrated only; R-2: detached only with a home on a 5,000+ sq ft lot.UDC 7.3.304E.1
  • DenverOne ADU per primary dwelling unit; in single-unit (SU) districts, one per zone lot, attached or detached. ADUs accessory to two-unit or multi-unit primaries must be detached.DZC §11.8.2.1.A.1–.2
  • Fort CollinsOne ADU per lot — attached or detached — accessory to a detached house, duplex, triplex, or mobile home, in every zone district since February 2025.LUC §3.1.8; Art. 2 zone tables
  • GreeleyOne ADU per lot, with a detached house or duplex/multi-unit building — detached or within the principal building (attic/basement). As codified, permitted only in the R-M, R-H, C-L, C-H, MU-L, and MU-H districts — not in R-E, R-L, or H-A, where single-family homes are permitted, an apparent conflict with the state statute.GMC §24-403.b; Table 24-4-2; contrast C.R.S. 29-35-403(1)
  • LakewoodOne ADU per lot, accessory to a single-family home — attached, detached, or over a garage. The old 9,000 sq ft minimum-lot rule was deleted in 2024. Allowed as a limited use in all R districts (and inside the permitted use's building in several mixed/commercial districts); prohibited in the industrial districts.§17.4.3.1.A.1, .3, .8–.11; Table 17.4.1
  • LongmontOne ADU per lot, accessory to a single-family detached home only — integrated, attached, or in a detached accessory structure (a garage works). No mobile homes, RVs, or trailers as ADUs.LMC 15.02.080.E.3.a–b
  • PuebloOne ADU — attached, detached, or integrated — accessory to a one-family residence, in any zone district (including PUDs) where one-family residences are allowed. Not permitted on lots with duplexes, townhouses, multi-family, mobile homes, or RVs.PMC 17-4-16(a), (b)(6)
  • ThorntonOne ADU per lot — interior, attached, or detached — accessory to a single-unit detached dwelling, permitted in the RE, RL, RM, RH, AG, and SFD-L districts.Dev. Code §18-339(b),(c),(e); Table 18-334.1
  • WestminsterOne ADU per lot — interior (basement/attic), attached, or detached — with any single-family detached home, in any zone where such homes are permitted.WMC 11-4-19(B)–(D)
Maximum size
  • ArvadaThe lesser of 40% of the home's living space and a lot-size tier: 600 sq ft on lots up to 6,000 sq ft; 850 up to 12,499; 1,000 up to an acre; 1,200 beyond. The 600 sq ft tier sits inside the 500–750 sq ft range state law protects — an apparent conflict. In-footprint conversions may reach 50% of the home including basement.LDC §5-1-5-2.E, Table 5-1-5-2; contrast C.R.S. 29-35-402(18)
  • Aurora650 sq ft — below the 750 sq ft the statute protects, one of several provisions in apparent conflict with state law.UDO §146-3.3.6.G.1.h; contrast C.R.S. 29-35-402(18)
  • BoulderAttached: the lesser of half the house's floor area or 1,000 sq ft (750 if the house is under 1,500). Detached: 800 sq ft. Affordable ADUs (rent capped at 75% AMI) and designated historic properties get more: attached to 1,200, detached to 1,000. Areas under 6-ft ceilings, mechanical rooms, and below-grade parking don't count.B.R.C. 9-6-3(n)(1)(A)(ii), Table 6-3
  • Colorado SpringsDetached: the lesser of 50% of the principal home's habitable area or 1,250 sq ft; if the home is under 1,500 sq ft, the ADU may still be 750 sq ft. ADU floor area is exempt from the accessory-structure area cap.UDC 7.3.304E.2.a
  • DenverSU districts: building footprint capped at 864 sq ft on lots of 7,000 sq ft or less, 1,000 sq ft on larger lots — footprint, not floor area, so a two-story unit can roughly double the space. Non-SU attached ADUs: up to the greater of 75% of the primary's floor area or 864 sq ft.DZC §11.8.2.1.B.2; §5.3.4.5
  • Fort CollinsNew detached: 750 sq ft if the home is under 1,667 sq ft, otherwise the lesser of 1,000 sq ft or 45% of the home. Converting an existing legal accessory structure: 800 sq ft. Attached: the greater of 750 sq ft or 45% (basement ADUs: up to the full floor).LUC §3.1.8 floor-area tables
  • GreeleyThe lesser of 60% of the home's living area or 1,200 sq ft; a detached ADU is additionally capped as a secondary building at 50% of the home's footprint (up to 1,200 sq ft). On small homes the 60% formula can block ADUs in the 500–750 sq ft range the statute protects.GMC §24-403.b.3; Table 24-5-2; contrast C.R.S. 29-35-402(18)
  • Lakewood1,400 sq ft of gross floor area — raised from 700 sq ft (with a one-bedroom cap, also deleted) by the June 2024 amendment. This generous cap predates the repealed rewrite and survives it.§17.4.3.1.A.6.a (O-2024-12)
  • Longmont500–800 sq ft regardless of the home's size — and larger is allowed up to 50% of the home's finished above-ground floor area, so 800 isn't a hard cap on bigger houses. Basement ADUs have no size limit at all.LMC 15.02.080.E.3.b.ii–iv
  • PuebloThe lesser of 100% of the residence's gross floor area or 800 sq ft.PMC 17-4-16(b)(7)
  • ThorntonThe greater of 1,000 sq ft or 50% of the home's gross floor area — garages, porches, and similar areas excluded from the calculation. Also exempt from the 5% accessory-use area cap.§18-339(k)(1)–(3)
  • WestminsterThe lesser of 1,200 sq ft or 50% of the home's gross floor area, minimum 190 sq ft, maximum two bedrooms — and where the home is under 1,500 sq ft, the ADU may still be up to 750 sq ft (codified March 2026 by Ordinance 4335).WMC 11-4-19(H); Ord 4335
Detached ADU height
  • Arvada25 ft in most RN subdistricts; 30 ft in RN-32.5, R6, R13, R24, and MX districts.LDC Table 2-1-3-3A (rows added by Ord 4905)
  • AuroraNo taller than the principal dwelling, and never more than 24 ft.UDO §146-3.3.6.G.1.i, .p
  • Boulder20 ft for a detached ADU; the manager may allow 25 ft with a roof pitch of 8:12 or steeper. Conversions of legal existing accessory buildings may keep their height and roof form.B.R.C. 9-6-3(n)(3)(A)
  • Colorado Springs16 ft for a detached ADU, regardless of roof type or pitch — council cut this from the prior 25/28-ft standard on the floor. Garage conversions: 25 ft. Attached/integrated: the zone maximum.UDC 7.3.304E.2.b (as amended 3/25/2025)
  • DenverUrban contexts: 2 stories / 24 ft with a side-lot-line bulk plane (12 ft on lots ≤40 ft wide, then 45°). Suburban: 1 story/17 ft, or 2 stories/24 ft with a 20-ft rear setback. The ADU must sit in the rear 35% (urban) or 50% (suburban) of the lot.DZC §5.3.4.5 form tables
  • Fort Collins1.5 stories / 28 ft, or the zone standard — Old Town caps at 24 ft or the house's height, whichever is less.LUC §3.1.8; §2.1.6
  • Greeley25 ft, but no taller than the principal structure — and larger secondary buildings also face a 9-ft wall / 22-ft roof-peak limit.Table 24-5-2; §24-502.c.2
  • LakewoodThe code conflicts with itself: Article 4 says 30 ft, Article 5's table says 20 ft (30 ft over a detached garage). The code's own rule that the more restrictive provision governs makes the effective answer 20 ft, or 30 ft over a garage — but get the city's reading in writing.§17.4.3.1.A.5.b vs. Table 17.5.1; §17.1.6.2.A
  • LongmontA detached ADU may not exceed the height of the principal structure.LMC 15.02.080.E.3.c.i
  • PuebloA detached ADU may not exceed the height of the residence on the lot; attached ADUs use the zone maximum (35 ft in most residential districts).PMC 17-4-16(b)(8)
  • ThorntonSame standards as the principal dwelling 'unless otherwise noted' — and the district tables note a split (e.g., RL: 35 ft for the house and for ADUs above a garage, 16 ft for other accessory structures), leaving ground-level detached ADU height ambiguous between the two numbers. Get the city's reading in writing.§18-339(f); Table 18-76.1 fn 7
  • WestminsterSame maximum height as the principal dwelling on the lot.WMC 11-4-19(G)
Detached ADU setbacks
  • ArvadaPrincipal-dwelling standards: RN interior side 5–15 ft, rear 10–15 ft by subdistrict — and zero rear setback where the lot abuts an alley. A detached ADU must sit at or behind the house's front plane (10 ft behind the façade on both frontages of a corner lot).LDC §5-1-5-2.B, .F; Table 2-1-3-3A
  • AuroraRear yard only; 5 ft side, 5 ft rear, 3 ft from the alley. An ADU atop an existing garage may keep the garage's setbacks.UDO §146-3.3.6.G.1.o; §146-4.2.3.F.1
  • BoulderAccessory-building setbacks: interior side and rear 3 ft; front 55 ft or behind the house's rear wall; 6 ft of separation from any other building. An attached ADU can extend into the rear setback under conditions (ADU-only space, 5 ft off the rear line, ≤500 sq ft, ≤20 ft tall).B.R.C. 9-7-1 Table 7-1; 9-6-3(n)(2)(B)
  • Colorado SpringsFront and side: same as the principal building. Rear: 5 ft. No detached ADUs in front yards; the old alley/above-garage setback rule was repealed.UDC 7.3.304E.2.c–d
  • DenverUrban: side 3 ft (lots ≤40 ft) or 5 ft; rear 5 ft without an alley — with an alley, 5 ft if garage doors face it, 0 ft if they don't. Suburban: side 3/5/7.5 ft by lot width; rear 10 ft (one story) or 20 ft (two). Vehicle access must come from the alley where one exists.DZC §5.3.4.5; §11.8.2.1.C.1
  • Fort CollinsAt least 5 ft from the house and 10 ft behind its front wall; side and rear per zone (RL example: side 5 ft, rear 15 ft — dropping to 5 ft along an alley).LUC §3.1.8; §2.1.4
  • GreeleySide and rear 5 ft; street side 20 ft; at least 12 ft behind the house's front building line and 6 ft from the house. No alley exception.Table 24-5-2; §24-502.c.1
  • LakewoodAnother internal wrinkle: the ADU section points at primary-structure standards (front 25 / side 15-10-5 / rear 15 ft in R districts), while the accessory-structure table gives 10 ft side/rear in the large-lot districts and 5 ft elsewhere, behind the front edge of the house. Large structures (any wall over 32 ft long or 12 ft high) take primary setbacks. The ADU can't sit in front of the house.§17.4.3.1.A.5; Table 17.5.1; §17.5.5.1
  • LongmontRear 5 ft, side 5 ft; no closer to the front line than the house (corner and multi-frontage lots get flexibility). An ADU inside an existing detached structure keeps its setbacks unless expanded.LMC 15.02.080.E.3.d
  • PuebloRear: 5 ft for ADUs up to 16 ft tall; taller units meet the zone rear setback. Front and side per zone standards.PMC 17-4-16(b)(9)
  • ThorntonSame as the principal dwelling unless noted. RL example: interior side 5 ft; rear 15 ft principal / 5 ft accessory on front-loaded lots; alley-loaded 10/0 ft (20 ft for an alley garage with driveway).§18-339(f); Table 18-76.1
  • WestminsterFront and side: same as the principal dwelling (per the applicable PDP/ODP). Rear: the greater of the district's accessory-building setback or 5 ft. No building over easements.WMC 11-4-19(F)
Off-street parking
  • ArvadaOne on-site space required for the ADU, in addition to the home's parking (tandem allowed) — broader than the narrow case where state law permits requiring a new space.LDC §5-1-5-2.D.1–2; contrast C.R.S. 29-35-403(3)
  • AuroraOne additional alley-accessed off-street space — and alley service is itself a prerequisite for the use. Both likely exceed what the statute permits.UDO §146-3.3.6.G.1.a, .k; contrast C.R.S. 29-35-403(2)(a), (3)
  • BoulderNone — the parking chapter contains no minimum vehicle-parking requirements for ADUs (or anything else; only maximums in two districts).B.R.C. 9-9-6
  • Colorado SpringsOne off-street space per ADU, in addition to the home's parking — council restored this after staff proposed zero. Stricter than the state statute's narrow parking allowance.UDC Table 7.4.10-A; contrast C.R.S. 29-35-403(2)(a), (3)
  • DenverNone. Denver repealed all minimum vehicle parking requirements citywide effective August 11, 2025.CB25-0684; DZC Div. 10.4
  • Fort CollinsNone for the ADU — only the home's own minimums apply, and a tandem space can count.LUC Div. 5.9; city ADU page
  • GreeleyAs codified: one space per bedroom for a 'secondary dwelling' (the term is undefined; applying it to ADUs is the plain reading), confined to the garage, driveway, or street directly in front — well beyond what the statute permits a city to require.Table 24-7-3; §24-403.b.4; contrast C.R.S. 29-35-403(2)(a), (3)
  • LakewoodConditional: parking applies only if on-street parking is 'legally or practically unavailable' (arterial/collector frontage, streets under 28 ft, or posted no-parking) — then one space per unit. Since June 30, 2025, the state statute further limits when a new space can be demanded; treat the statute as controlling where more permissive.§17.4.3.1.A.6.e; Table 17.8.1; C.R.S. 29-35-403(3)
  • LongmontNone required, and no more than two spaces may be provided. (The city's guide describes a statute-shaped one-space exception for lots with no off-street parking and no on-street option — not yet visible in the codified text.)LMC 15.02.080.E.3.f
  • PuebloOne space only if all three statutory conditions apply (no existing usable off-street space; the zone required parking as of January 1, 2024; the block prohibits on-street parking) — otherwise an existing surplus space is simply designated to the ADU. Statute-verbatim.PMC 17-4-16(b)(10)–(11)
  • ThorntonOne space per ADU, on the same lot and shown on the development-plan site plan. The statute only allows requiring a new space in a narrow three-condition case; how Thornton applies this is untested.Table 18-650.1; §18-339(h); contrast C.R.S. 29-35-403(3)
  • WestminsterNone in most cases — the home keeps its own minimum. One new space only if no existing off-street spot could serve the ADU AND on-street parking is prohibited on the block. Statute-verbatim.WMC 11-4-19(I)
Owner-occupancy
  • ArvadaStill required, ongoing: the owner must occupy the house or the ADU, enforced by a recorded deed restriction that ties the ADU's certificate of occupancy to continued owner occupancy and bars separate sale. State law has barred ongoing owner-occupancy requirements since June 30, 2025; Arvada's August 2025 amendment left this in place.LDC §5-1-5-2.K, .L; contrast C.R.S. 29-35-403(2)(b)
  • AuroraStill codified: the owner must occupy the primary dwelling or the ADU. Preempted on paper by state law since June 30, 2025, but not repealed.UDO §146-3.3.6.G.1.l; contrast C.R.S. 29-35-403(2)(b)
  • BoulderNot required since March 8, 2025 — the city's page says so explicitly, and no owner-occupancy standard survives in the code.City ADU page; B.R.C. 9-6-3(n) (absence verified)
  • Colorado SpringsApplication-time only: an owner-residency affidavit when applying, with an exception for ADUs built simultaneously with a new home. The old ongoing owner-occupancy and recorded declaration were repealed.UDC 7.3.304E.1.a
  • DenverNo ongoing occupancy requirement. In SU districts, both units must stay under common ownership, and an owner must occupy the primary home at the time of permit application when adding an ADU to an existing house (waived for simultaneous new construction and DHA properties) — the exact carve-out state law allows.DZC §11.8.2.2.A–.B; C.R.S. 29-35-403(2)(b)
  • Fort CollinsNone — no owner-occupancy language anywhere in the code.LUC (verified absence); C.R.S. 29-35-403(2)(b)
  • GreeleyNone — the ADU section contains no owner-occupancy condition.GMC §24-403.b
  • LakewoodPermit-issuance only: an ADU permit issues to an owner-occupant or their designee — no ongoing occupancy requirement and no recorded covenant (the 2024 amendment deleted both). Consistent with the state statute's application-time allowance.§17.4.3.1.A.4 (O-2024-12); C.R.S. 29-35-403(2)(b)
  • LongmontNo ongoing requirement — but the applicant must prove City of Longmont residency at application (Colorado ID plus two supporting documents), waived when the ADU is built together with a new home. Note the statute's carve-out is residency on the parcel; Longmont's city-wide version reads more broadly.LMC 15.02.080.E.2; C.R.S. 29-35-403(2)(b)
  • PuebloApplication-time only: proof of occupancy (a utility or medical bill, first-class mail, or bank statement within 12 months) when applying. No ongoing requirement.PMC 17-4-16(b)(1)
  • ThorntonStill required, ongoing: the owner of record must occupy either the house or the ADU, and a recorded deed restriction ties the ADU's certificate of occupancy to continued owner occupancy. This directly conflicts with C.R.S. 29-35-403(2)(b), which bars ongoing owner-occupancy requirements for subject jurisdictions — Thornton is one, and the state listed it as non-compliant in October 2025.§18-339(l), (n)(1)(c); DOLA Oct 2025 determination
  • WestminsterNone — the city's own FAQ confirms you may live in the ADU and rent out the main house.WMC 11-4-19 (full section); city ADU guide FAQ
Lot coverage / floor area
  • ArvadaDistrict standards apply (RN lot coverage 25–40% by subdistrict); in the OT district the ADU footprint is capped at the lesser of 800 sq ft or 40% of the house's footprint.LDC §5-1-5-2.B; Table 2-1-5-10B
  • AuroraLot must exceed 6,000 sq ft; the ADU may cover no more than 50% of the rear yard, and 360 sq ft of usable private open space (minimum dimension 10 ft) must remain.UDO §146-3.3.6.G.1.e, .g
  • BoulderThe lot must still meet district FAR and building-coverage limits, and accessory buildings between the house's rear setback and the rear lot line are capped at 500 sq ft of cumulative coverage in the RR/RE/RL/RMX-1 districts.B.R.C. 9-7-1 Table 7-1; 9-7-8(a)
  • Colorado SpringsADU exempt from the combined accessory-structure floor-area cap; zone lot-coverage and dimensional tables still apply.UDC 7.3.304E.2.a; Part 7.4.2
  • DenverA detached ADU counts toward the primary form table's maximum building coverage (Urban House: 60/45/40% by lot width). No ADU-specific bonus.DZC §5.3.4.5; Art. 5 form tables
  • Fort CollinsADU floor area is excluded from Old Town's rear-lot floor-area caps and from the RL district's minimum-lot-area ratio — deliberate carve-outs that keep ADUs from eating the lot budget.LUC §2.1.6; §2.1.4
  • GreeleyGreeley uses minimum lot open space per building type rather than a maximum coverage; the detached ADU also lives under the 50%-of-footprint secondary-building cap.Table 24-5-1; §24-503
  • LakewoodAccessory structures combined: at most 50% of the rear/side/non-primary-front yard area and 10% of the total lot; zone minimum open space runs 25–65% by district.§17.5.5.1.B.1; Table 17.5.1
  • LongmontAll accessory structures combined may not exceed 75% of the home's floor area — which can force removing or shrinking existing sheds and garages to fit an ADU. ADUs are excluded from density calculations.LMC 15.04.040.B.1; 15.03.070.B.3.e
  • PuebloADUs are exempt from the accessory-building chapter entirely — including its 15%-of-lot / 1,500 sq ft caps. The zone's general lot coverage (50% in most residential districts) still applies.PMC 17-4-23(a)(7); 17-4-2(d)
  • ThorntonAll accessory buildings combined, ADU included, must stay within the district's maximum lot coverage (RL 85%, RE 45%).§18-336(b)(2); Tables 18-75.1/76.1
  • WestminsterThe combined footprint of the home and ADU must stay within the principal dwelling's maximum lot coverage; where PUD documents are silent, no maximum applies.WMC 11-4-19(E)
Permit path & timeline
  • ArvadaAdministrative building permit via eTRAKiT, with a licensed contractor required. Published review timelines — rare and welcome: about 3 weeks for a detached (Type A), 1–2 weeks for an interior/attached (Type B).City ADU page; LDC §3-1-2-1.B
  • AuroraConditional use with a Planning Commission public hearing — the opposite of the administrative approval state law mandates. No published timeline.UDO Table 3.2-1; contrast C.R.S. 29-35-403(1)
  • BoulderBuilding permit only — the prior administrative-review step was eliminated in September 2023. ADUs in old PUD areas are approved as minor modifications, and prior PUD ADU bans are void. No published timeline.City ADU page; B.R.C. 9-6-3(n)(1)(A)(viii)
  • Colorado SpringsAdministrative — site plan plus building permit, decided on objective standards; utility ability-to-serve determination required, plus a 14-day posted public notice before the permit issues. No land-use application fee. No published review timeline.UDC 7.3.304E.1.i–j
  • DenverUse by right citywide where single-unit dwellings are allowed — no rezoning since December 2024. Zoning permit + building permit + sewer use & drainage permit; a licensed contractor is required (homeowners can't self-permit). No fixed timeline — the city publishes only a live average-review-times dashboard.CB24-1302; Denver CPD ADU permits page
  • Fort CollinsBasic Development Review — a staff decision — in every zone, then a building permit; a free conceptual design review is offered first. The BDR flat fee is $6,925, and the city itself pegs typical total fees at $20,000–25,000. No published day-count for review.LUC Div. 4.2; city ADU page
  • GreeleyPermitted accessory use — staff review and/or site plan approval, then a building permit via eTRAKiT. Published plan-review times: 20 working days for new construction, 10 for additions and remodels.§24-402.a.1(a); city building-permits page
  • LakewoodAdministrative Review of Supplemental Standards (no hearing, no public input) — and the director must decide within 15 days of a complete application, one of the fastest codified clocks anywhere — plus residential design standards and the building permit.§17.4.3.1.A.7; §17.2.12.2.B.2
  • LongmontBuilding permit through the Chief Building Official — a five-step checklist process with multi-department plan check. No published timeline; typical city fees run $5,000–$10,000, plus school fees.LMC 15.02.080.E.1; city ADU guide
  • PuebloAdministrative approval plus a building permit via the regional building department. The state reviewed the draft for statutory compliance before adoption. No published timeline.PMC 17-4-16; TA-22-03 staff packet
  • ThorntonAdministrative development plan (director-approved) plus building permit; the ADU's certificate of occupancy requires the home's CO first, and water/sewer capacity verification is required. Small or non-visible projects (≤500 sq ft, or not visible from the right-of-way) skip the development plan. No published timeline.§18-339(g)–(j); §18-41(b)
  • WestminsterAdministrative only — staff-approved building permit via the eTRAKiT portal, no public hearing, no ODP amendment, and no HOA approval required. Published staff review timeline: up to 4 weeks.WMC 11-4-19(K)–(N); city ADU guide

City pages

Arvada · Aurora · Boulder · Colorado Springs · Denver · Fort Collins · Greeley · Lakewood · Longmont · Pueblo · Thornton · Westminster

Verified 2026-08-19 against codified municipal code and adopted ordinance text. See methodology and the changelog.