Boulder ADU Zoning Rules & Permit Guide

ADU Regulations in Boulder, Colorado

Updated September 29, 2026

At the foothills of the Flatirons in Boulder County, the city maintains one of Colorado's most thorough ADU review processes. Green building requirements, design review, and strict owner occupancy rules reflect the city's environmental and community values.

Below is a summary of the key zoning rules applicable to Accessory Dwelling Units in Boulder as of 2026. Regulations are governed by local zoning ordinances, as Colorado has no statewide ADU mandate (HB 24-1152 addresses transit density).

Additional Local Requirements for Boulder

• ADU on lots 5,000 sq ft minimum
• Detailed design review process required
• Green building requirements apply
• Short-term rentals strictly prohibited
• Boulder has its own specific ADU ordinance

Frequently Asked Questions About ADUs in Boulder

Can I build an ADU in Boulder?

Boulder has a rigorous ADU approval process with design review and green building standards. Plan for a longer permitting timeline.

What is the maximum ADU size allowed in Boulder?

ADUs in Boulder can be up to 1,200 square feet, subject to the property's zoning and lot coverage limits. Always confirm the exact allowed size with the Boulder planning department before designing your project.

What are the setback requirements for an ADU in Boulder?

ADUs in Boulder generally require setbacks of 5 ft rear, 5 ft side. Colorado has no statewide ADU mandate, so the exact setback figures come from Boulder's own zoning code — confirm them with the city planning department before you design.