ADU (Accessory Dwelling Unit) Permit in Boulder (2026)

Can I build an ADU on my Boulder property?

Yes. Colorado HB 24-1175 (effective August 2024) requires Boulder to allow ADUs by-right on all single-family lots. Boulder already had an ADU program in place and has updated its code to comply. ADUs are limited to 1,000 sqft (Colorado does not use California's JADU concept). No owner-occupancy is required. Boulder also has a voluntary deed restriction program — ADUs committed to income-limited rentals receive reduced permit fees. Contact Boulder Planning at (303) 441-1880 or apply online.

What is Boulder's Open Space Mountain Parks Blue Line and how does it affect housing?

Boulder's Blue Line (formally established in 1967) defines the maximum elevation at which the city will extend its water service — approximately the 5,750-foot contour line following the mountain foothills. Properties above the Blue Line cannot receive city water, effectively preventing development. Boulder has purchased over 46,000 acres of open space surrounding the city (OSMP program). This creates a hard urban growth boundary making Boulder geographically constrained, driving up property values and housing costs significantly. All ADU development occurs within the established urban service area below the Blue Line.

How does Boulder's high altitude affect ADU construction?

Boulder's elevation of 5,430 feet (1,655 meters) affects construction in several ways. Energy code: higher insulation requirements due to cold winters (average January low: 20°F) and greater heating loads. Snow load: ground snow load of 30 lbs/sqft — all structures require structural design for this load. UV radiation: high-altitude UV is approximately 20% more intense than sea level — use UV-resistant exterior materials and expect faster weathering of wood and paint. Heat pump sizing: cold-climate heat pumps rated to -15°F or lower are recommended. Solar production: higher altitude increases solar panel output (less atmosphere to filter UV).

Can I do Airbnb in Boulder near the University of Colorado?

Yes, with a Boulder Short-Term Rental License ($150/year). Primary residence requirement applies — you must live there as your principal residence. Whole-home STRs are capped at 120 nights per year when you're not present. CU Boulder creates strong STR demand during football weekends, graduation, and conference periods. Boulder's Accommodations Tax (7.9%) is collected by Airbnb and VRBO. Be aware that CU's fall arrival (late August) and spring graduation (May) are peak STR pricing periods in University Hill and Mapleton Hill neighborhoods.

What is Boulder's voluntary deed restriction program for ADUs?

Boulder's Affordable Accessory Dwelling Unit Program allows homeowners to voluntarily commit their ADU to income-restricted rents in exchange for reduced permit fees and other incentives. ADU rents are limited to 75% of area market rate (approximately $1,200–$1,800/month for studios) and tenants must meet income eligibility (120% AMI or below). The deed restriction typically runs 20+ years. This program was created to increase ADU affordability given Boulder's extreme housing costs. Contact Boulder Planning at (303) 441-1880 for details on current fee reductions and program terms.

How does Boulder differ from Denver for ADU rules?

Both Boulder and Denver follow Colorado HB 24-1175 statewide preemption: no owner-occupancy required, ministerial approval within 60 days, limited parking requirements. Key differences: Boulder limits ADUs to 1,000 sqft; Denver allows 1,000 sqft with similar 50% primary dwelling cap. Boulder's permit fees are higher than Denver's reflecting its premium service. Boulder is served by Xcel Energy; Denver is also Xcel. Boulder's voluntary deed restriction program for affordable ADUs is unique. Boulder's Open Space boundary limits growth differently than Denver's more expansive metro geography. Boulder's housing costs (median home price $900,000+) make ADU rental income particularly compelling.