Westminster, CO Accessory Structures: ADU Rules (2026)
ADU rules in Westminster, CO, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Governing section
- W.M.C. Section 11-4-19
- ADUs per lot
- One accessory dwelling unit
- Size range
- 190 to 1,200 sq ft
- Bedroom limit
- Maximum two bedrooms
- Approval process
- Administrative, no public hearing
- Rear setback
- Accessory-building standard or 5 ft, greater
Summary
Westminster permits one accessory dwelling unit per single-family lot, sized 190 to 1,200 square feet with no more than two bedrooms, approved administratively without a public hearing under Section 11-4-19.
(D)Number Permitted: One accessory dwelling unit is allowed per lot...(H)Size Requirements:(1)The minimum size for an accessory dwelling unit shall be 190 square feet.(2)The maximum size for an accessory dwelling unit shall be 1,200 square feet, or 50 percent of the gross floor area of the principal dwelling unit, whichever is less.(3)No accessory dwelling unit shall have more than two bedrooms.(K)Administrative Approval: Approval of accessory dwelling units shall not require, and may not be elevated to require, a public hearing, a recommendation or a decision by an elected or appointed public body or a hearing officer, provided the accessory dwelling unit meets all requirements of this section.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 12).
Full Breakdown
Section 11-4-19 allows accessory dwelling units (ADUs) on any lot with a permitted single-family detached dwelling, whether the ADU sits inside, attached to, or detached from the principal home. Only one ADU is allowed per lot, and it must have its own address and a separate entrance from the principal unit. Size is tightly bracketed: the minimum is 190 square feet and the maximum is 1,200 square feet or 50 percent of the principal dwelling's gross floor area, whichever is less, and it cannot have more than two bedrooms.
Freestanding ADUs must sit on a permanent foundation; mobile homes and RVs cannot be used. Height and front/side setbacks must match the principal dwelling, while rear setbacks follow the accessory-building standard for the zone or five feet, whichever is greater, and combined lot coverage of both units cannot exceed the cap set for the principal dwelling alone. A new parking space is required only if the principal unit lacks an existing off-street space and the block prohibits on-street parking. Architecturally, the ADU must match the principal home in at least three listed elements, such as roof pitch, siding material, or window style.
Under Subsection (K), approval is administrative and cannot be elevated to a public hearing, and a certificate of occupancy cannot issue until the principal dwelling already has one.
Violations & Fines
Constructing an ADU without required building and utility permits, exceeding the size, bedroom, or one-per-lot limits, or selling the ADU separately from the principal dwelling violates Section 11-4-19; the Code allows a Planning Commission variance under Section 2-2-8, but only for the architectural-character standard, and only if the variance will not alter the essential character of the neighborhood.
Frequently Asked Questions
How many accessory dwelling units can I build in Westminster?
Do I need a public hearing to build an ADU in Westminster?
Can I sell my accessory dwelling unit separately in Westminster?
Sources & Official References
Other rules in Westminster
How Westminster compares: Easiest Cities to Build an ADU·Compare Westminster to another location·View the Colorado accessory structures overview
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