Accessory Dwelling Unit (ADU) Permit in Westminster, Colorado

Westminster requires an accessory dwelling unit (adu) permit for: 1 ADU allowed per primary dwelling unit on the same lot; Permitted in any zone that allows single-family detached dwelling units as a use; ADU may be located within the principal dwelling (e.g., basement/attic with private entrance), attached as an addition, or as a separate detached building on the same lot; Must be on a permanent foundation; all codes applicable to residential construction apply, including the IRC and Fire Code (including fire sprinklers where required); Full kitchen facilities and a full bathroom are required; Principal dwelling must have a Certificate of Occupancy; the ADU requires its own separate Certificate of Occupancy; ADU must have its own address (assigned during the review process); apply for the permit under the principal dwelling's address; Minimum size: 190 sq ft. Maximum size: 1,200 sq ft or 50% of the principal dwelling's gross floor area, whichever is less (up to 750 sq ft allowed where the principal dwelling is under 1,500 sq ft; ADU may never be larger than the principal dwelling); Setbacks: front and side match the principal dwelling's required setbacks; rear setback is the greater of the accessory-structure setback or 5 feet; ADUs may not be built over an easement; Engineered plans prepared by a licensed professional, drawn to scale and specific to the property, are required; No City-imposed restriction on ADU rental rates. If your project isn't listed, confirm with City of Westminster — Department of Community Development, Building Division at 303-658-2075 before starting work.

In Westminster, the published Building Permit Fee — valuation-based (same tiers as new construction) is: Varies by valuation — see Residential Building Permit fee tiers. Additional published fees: Plan Review Fee — 65% of the Building Permit Fee; Use Tax — 4.25% of 50% of Total Valuation; Utility Tap Fees — Varies — determined by Westminster Public Works and Utilities (PWU). These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Plan review for an accessory dwelling unit (adu) permit in Westminster typically runs 1–1 business days. This is an estimate, not a published figure — confirm current review times with City of Westminster — Department of Community Development, Building Division at 303-658-2075.

You'll need: Building Permit Application (eTRAKiT); Accessory Dwelling Unit Info Sheet (Rev. 5, March 10, 2026); Engineered Construction Plans. See the required-documents checklist on this page for details on each.

Westminster requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing, MEP Rough-In, Final. Schedule each through City of Westminster — Department of Community Development, Building Division (303-658-2075).

Apply through City of Westminster — Department of Community Development, Building Division at 4800 W. 92nd Avenue, Westminster, CO 80031. Phone: 303-658-2075, email: permits@westminsterco.gov. Office hours: Mon–Fri, 8 a.m.–5 p.m. (front office); residential permit review walk-through times: Tuesdays 1–4:30 p.m. and Thursdays 9 a.m.–noon; all permits must be applied for online via eTRAKiT. Official information: https://www.westminsterco.gov/621/Building-Division.

One ADU is allowed per primary single-family detached dwelling unit on the same lot, per the City Council-approved ADU regulations effective January 1, 2025.

1,200 sq ft or 50% of the principal dwelling's gross floor area, whichever is less. If the principal dwelling is under 1,500 sq ft, the ADU may be up to 750 sq ft, but never larger than the principal dwelling itself. Minimum size is 190 sq ft.