Accessory Dwelling Unit (ADU) Permit in Westminster, Colorado
Required for construction of a new attached or detached ADU on a single-family detached lot in Westminster. City Council newly authorized ADUs citywide on November 18, 2024, effective January 1, 2025 — the same codes that apply to residential construction (2021 IRC, Fire, utility connections) apply to ADUs.
Verified 2026-06-30 · Source
When you need this permit
- 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
Required documents
- Req
Building Permit Application (eTRAKiT)
Apply under the principal dwelling unit's address; ADU permits follow the standard residential permit process
- Req
Accessory Dwelling Unit Info Sheet (Rev. 5, March 10, 2026)
City of Westminster's current ADU provisions guide: allowance, size, setbacks, design, address, fees
- Req
Engineered Construction Plans
Prepared by a licensed professional, drawn to scale, specific to the property, meeting the 2021 IRC and Design Criteria for Structures
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Building Permit Fee — valuation-based (same tiers as new construction) | Varies by valuation — see Residential Building Permit fee tiers | ADU Info Sheet (Rev. 5): 'Building Permit fees, as determined by Building' |
| Plan Review Fee | 65% of the Building Permit Fee | ADU Info Sheet: 'Building Review fees, as determined by Building' |
| Use Tax | 4.25% of 50% of Total Valuation | ADU Info Sheet: 'Use Tax fees, as determined by Building' |
| Utility Tap Fees | Varies — determined by Westminster Public Works and Utilities (PWU) | ADU Info Sheet: 'Utility tap fees apply, as determined by PWU' — the Info Sheet explicitly states this is not an exhaustive fee list and other development/impact fees may apply; confirm exact tap fee at application via the Water Tap and Sewer Fees page |
Review timeline
~1–1 business days
Typical estimate — confirm current times with the Westminster building department
Inspection process
- 1
Foundation
Footings and foundation before concrete pour — 36-inch frost depth minimum
- 2
Framing
Structural framing, egress windows, fire separation (if attached)
- 3
MEP Rough-In
Mechanical, electrical, plumbing rough-ins before walls closed
- 4
Final
All work complete; ADU requires its own separate Certificate of Occupancy
Tips
- Westminster's ADU ordinance is very new: approved by City Council November 18, 2024, effective January 1, 2025 — confirm current zoning eligibility since this is a recently-changed program.
- An ADU needs its own separate Certificate of Occupancy in addition to the principal dwelling's CO.
- There is no City-imposed cap on ADU rental amounts.
- Exact utility tap fees are determined by Westminster Public Works and Utilities (PWU), not the Building Division — confirm the specific dollar figure before budgeting, since the ADU Info Sheet does not publish a flat tap-fee number.
Frequently asked questions
- How many ADUs can I build in Westminster?
- 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.
- What is the maximum size of an ADU in Westminster?
- 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.
Sources & verification
Verified against official sources. Last reviewed 2026-06-30.
- City of Westminster — Department of Community Development, Building Division — official building department
- Accessory Dwelling Unit Info Sheet, Rev. 5 (March 10, 2026) (PDF)
- City of Westminster — Resources (Building Division guide index)
Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Westminster building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.
Other permits in Westminster
Related guides
Get the AI compliance checklist
Upload your project scope, get a jurisdiction-specific checklist of everything you need. Coming soon.
We only use your email to send permit updates. No spam, unsubscribe anytime. Privacy.