Accessory Structures in Boulder, CO (2026)
5 verified accessory structures rules for Boulder, Colorado, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
Boulder caps a detached accessory dwelling unit at 800 square feet, or 1,000 square feet if affordable, and an attached ADU at half the principal home's floor area or 1,000 square feet, whichever is less. Every rented ADU needs a city rental license, and short-term rental of an ADU is banned outright.
Boulder Accessory Dwelling Unit Size and Rental Rules
Some RestrictionsBoulder Revised Code § 9-6-3(n)
(n)Accessory Dwelling Unit:(1)...(A)General Standards:...(i)Lot Limitations: An accessory dwelling unit may be established on a lot with one detached dwelling unit. One accessory dwelling unit may be located on a lot.(ii)Maximum Floor Area: The accessory dwelling unit shall be limited to the maximum floor area set forth in Table 6-3...(iii)Rental License: No owner of the property shall allow......
ADU Impact Fees
Accessory dwelling units built to the standards of Boulder Revised Code section 9-6-3 are exempt from the city's affordable housing capital facility impact fee under section 8-9-3(c)(6). That is separate from the smaller exemption for additions of 500 square feet or less, and it applies specifically to the floor area that makes up the ADU itself.
Boulder ADU Affordable Housing Fee Exemption
Few RestrictionsBoulder Revised Code § 8-9-3(c)(6)
(4)Small Additions to Residential Uses: ... An accessory building of a residential use or an addition to an existing single unit dwelling of five hundred square feet or less shall be exempt from paying the affordable housing impact fee. This exemption shall only be used one time for each dwelling unit in existence on January 31, 2026.(5)Single-Unit Dwellings: Any floor area in a single-unit dwe...
ADU Rental Restrictions
Boulder requires a rental license before anyone occupies an accessory dwelling unit (ADU) or the paired principal dwelling as a paying tenant, bars short-term renting of either unit on an ADU lot unless separately licensed, and forbids selling the ADU apart from the main house. Each rule sits in Subparagraph 9-6-3(n)(1)(A) of the land use code.
Boulder ADU Rental License and Sale Rules
Significant RestrictionsBoulder Revised Code § 9-6-3(n)(1)(A)(iii)-(v)
(iii)Rental License: No owner of the property shall allow, or offer to allow through advertisement or otherwise, any person to occupy the accessory dwelling unit or the principal dwelling unit as a tenant or lessee or otherwise for a valuable consideration unless such rented unit has been issued a valid rental license by the city manager consistent with the requirements of Chapter 10-3, "Rental...
Shed & Carport Rules
In Boulder's RR, RE, RL, and RMX-1 residential zones, sheds and other accessory buildings sitting in the rear yard setback area are capped at a combined 500 square feet of building coverage under Section 9-7-8(a), B.R.C. 1981, unless the property is an individual landmark or in a historic district.
Boulder Accessory Building Coverage Cap: 500 SF
Some RestrictionsSec. 9-7-8(a), B.R.C. 1981
(a)Maximum Building Coverage: In an RR, RE, RL or RMX-1 residential zoning district, unless the property has been designated as an individual landmark or is located within a historic district under Chapter 9-11, "Historic Preservation," B.R.C. 1981, the total cumulative building coverage of accessory buildings or structures between the principal building rear yard setback and the rear yard prop...
Tiny Homes
Boulder allows site-built tiny houses as single dwelling units under Appendix BB of its Residential Building Code, BRC 10-5.5-2(jj). The catch: a tiny house must sit on a permanent foundation and connect permanently to utilities like any other dwelling, so a tiny house on wheels doesn't qualify as a code-compliant dwelling under this appendix. Off-site built tiny houses follow a separate state manufacturing statute instead.
Boulder Tiny House Building Standards
Some RestrictionsBRC § 10-5.5-2(jj), Appendix BB, § BB101.1
(jj)Appendix BB, "Tiny Houses," is hereby repealed and reenacted to read as follows: APPENDIX BB TINY HOUSES The requirements of Appendix BB to the 2024 edition of the International Residential Code of the International Code Council shall hereby be complied with which appendix is hereby adopted by reference as part of the City of Boulder Residential Code and have the same force and effect as th...
Looking for Boulder County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Boulder city rules.
Accessory Structures in Boulder County →