Westminster ADU rules
✓ Verified against code · August 19, 2026
Current rules under WMC 11-4-19 (Westminster Municipal Code), adopted by Ordinance 4272 (amended by Ord 4335), in effect since January 1, 2025. Westminster complied six months early (January 1, 2025) with clean, statute-shaped rules — then amended once more in March 2026 (Ordinance 4335, at the state's insistence) to guarantee small-home owners the statutory 750 sq ft. One of the smoothest adoptions on the Front Range, with a published review timeline to match.
Common questions, answered from the code
How big can a Westminster ADU be?
The lesser of 1,200 sq ft or half the home's floor area, with two protections: a 190 sq ft minimum, and — since March 2026 — a guarantee that owners of homes under 1,500 sq ft can still build up to 750 sq ft. Maximum two bedrooms.
WMC 11-4-19(H); Ord 4335 · Permalink
How long does a Westminster ADU permit take?
The city publishes an answer, which is rare: staff review can take up to 4 weeks, fully administrative — no hearing, no ODP amendment, no HOA sign-off required.
City ADU guide; WMC 11-4-19(K) · Permalink
Does Westminster charge impact fees on ADUs?
No — no park, school, or land-dedication fees apply to ADUs, which materially changes the budget versus neighboring cities.
City ADU guide · Permalink
Do I have to live on the property?
No — there's no owner-occupancy requirement at all, and the city's FAQ explicitly blesses living in the ADU while renting out the main house.
WMC 11-4-19; city FAQ · Permalink
The rules at a glance
| ADUs allowed per lot | 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 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 | Same maximum height as the principal dwelling on the lot.WMC 11-4-19(G) |
| Detached ADU setbacks | 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 | 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 | 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 | 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 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 |
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.
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.
Check your parcel
The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:
- Adams County Property Portal (Assessor Search)
- Jefferson County Assessor Property Search
- Westminster zoning map (City GIS)
Primary sources
Other Colorado cities
Arvada · Aurora · Boulder · Colorado Springs · Denver · Fort Collins · Greeley · Lakewood · Longmont · Pueblo · Thornton
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. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.