Accessory Structures in Westminster, CO: What Residents Actually Need to Know

If you live in Westminster or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Westminster has 2 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Shed & Carport Rules

Westminster homeowners can skip a building permit for a detached tool shed, playhouse, gazebo, or pergola only if its floor area stays at or under 120 square feet, under Section 11-9-3(A)(2) of the Municipal Code. A shed of 121 square feet or larger, or any accessory structure with plumbing or electrical service, needs a full permit.

Key details: Governing section: Municipal Code § 11-9-3(A)(2). Exempt shed size: 120 square feet or less, one story. Covered uses: Tool sheds, playhouses, gazebos, pergolas. Zoning still applies: Exemption does not waive setback rules. Oversized shed: Requires full building permit and inspection.

Building an oversized accessory structure without first obtaining a permit doubles the eventual permit fee to a minimum of $250.00 for a first offense and $500.00 for later offenses under Section 11-9-3(E)(5), and the Building Official can order the work stopped until a permit is obtained. A shed that violates zoning setbacks despite being permit-exempt can still be ordered removed as a code violation.

ADU Rules

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.

Key details: 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.

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.

The Bottom Line

Westminster's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Westminster is broadly strict or permissive.

These rules come from Westminster's publicly available municipal code. For complete penalty schedules, exemption details, and answers to common questions, see the individual ordinance pages throughout this guide.