Arvada vs. Westminster ADU rules
Arvada and Westminster show the gap between a city that resisted state ADU compliance and one that moved early. Westminster's rules (WMC 11-4-19) took effect January 1, 2025 with no owner-occupancy requirement at all and no parking mandate except in the statute's narrow case, plus a 2026 amendment (Ordinance 4335) guaranteeing small-home owners up to 750 sq ft. Arvada's 2022 code, amended in August 2025 without fixing the conflicts, still requires ongoing owner-occupancy enforced by a recorded deed restriction, mandates one parking space per ADU regardless of need, and caps small-lot ADUs at 600 sq ft under LDC §5-1-5-2.E — reasons the state listed Arvada as non-compliant in October 2025.
✓ Verified against code · August 19, 2026
Arvada rules run under Land Development Code §5-1-5-2, adopted by 2022 LDC (Ord 4793), amended by Ord 4905, in effect since March 21, 2022.
✓ Verified against code · August 19, 2026
Westminster rules run under WMC 11-4-19 (Westminster Municipal Code), adopted by Ordinance 4272 (amended by Ord 4335), in effect since January 1, 2025.
Rule by rule
| Rule | Arvada | Westminster |
|---|---|---|
| ADUs allowed per lot | One 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 | One 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 | The 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) | The 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 | 25 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) | Same maximum height as the principal dwelling on the lot.WMC 11-4-19(G) |
| Detached ADU setbacks | Principal-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 | Front 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 | One 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) | None 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 | Still 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) | None — 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 | District 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 | The 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 | Administrative 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 | Administrative 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 |
Arvada: worth knowing
- ADU utilities must share the home's water and sewer services — no separate taps allowed (the opposite of Everett, WA's separate-meter mandate).
- One short-term rental per property; the ADU may be the licensed STR unit.
- The city's page notes HOA approval — though state law limits HOA ADU bans.
- Closing out the permit takes more than inspections: an improvement location certificate, grading certification, blower-door test, and recorded covenants are all required.
- Arvada is a plaintiff in the six-city home-rule lawsuit — but that case targets other housing laws, not the ADU statute it currently conflicts with.
Arvada: on our watchlist
No corrective ordinance found through August 2026 (the only 2026 LDC amendment covered short-term rentals) — the state-conflict provisions are the top watchlist item.
The six-city home-rule lawsuit (other statutes) remains pending.
Westminster: worth knowing
- No impact fees — no park, school, or land-dedication charges on ADUs, unusual for the region.
- Architectural match: 3 of 7 listed elements must match the main house, with a simplified single-criterion variance path.
- Short-term rental of an ADU is allowed with a license.
- Permanent foundation required — no tiny homes on wheels or RVs; engineered plans required.
- The March 2026 small-home fix came at the state's insistence — an example of the compliance-review process actually working.
Westminster: on our watchlist
A citywide Unified Development Code rewrite is in drafting — ADU provisions could move or change on adoption; we re-check each pass.
Full detail: Arvada · Westminster · back to the Colorado hub. Not legal advice — every fact above cites the code section it comes from; check the cite, or ask your city’s planning department to confirm your specific lot.