Boulder, CO Accessory Structures: ADU Rental Restrictions (2026)

Boulder's rental framework is the most rigorous in Colorado. Long-term rental (leases of 30+ days) of an ADU requires a Rental Housing License under BRC Title 10 Chapter 3. Both new and renewal licenses require a Rental Licensing Inspection on the International Property Maintenance Code standard plus a SmartRegs energy efficiency inspection — Boulder is one of the few U.S. cities that ties rental licensing to energy performance. For multi-unit dwellings, inspections cover 10% of units (minimum one). Multi-unit properties that submit Lighting Certification receive a four-year license term; those that do not get a one-year reduced term, extendable to four years if certification is submitted in the first year. The Rental Inspection Compliance Verification Form must be completed by a Boulder-licensed inspector. Short-term rental of an ADU is governed by BRC 10-3-18 and is much tighter: the host must use the dwelling as their principal residence (primary-residence requirement survived the 2025 ADU reforms because it applies to the host, not as an owner-occupancy condition on the ADU itself), hold a city STR License, register with the City Manager, and collect Boulder's Accommodations Tax along with state and county lodging taxes. The intersection of these rules is that an ADU may be short-term rented only when its operator lives in it as their primary residence — a common configuration is the owner living in the ADU and STR-ing it occasionally while traveling. Long-term ADU rental without owner residency is now fully permitted but the rental license, inspection, and SmartRegs energy compliance remain mandatory.