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Zoning Guide

ADU Rules in Boulder, Colorado

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ADU Rules in Boulder, Colorado

Boulder is home to the University of Colorado and is known for its progressive planning policies and growth management controls. ADUs are permitted, but Boulder has unique occupancy limits and housing affordability programs that affect ADU use. Housing in Boulder is extremely expensive and ADUs are in high demand.

Permitted ADU Types

  • Detached ADU (Accessory Unit): Standalone structure on the lot
  • Attached ADU: Addition to primary home with own entrance
  • Carriage House: Dwelling above detached garage
  • Basement ADU: Converting basement to separate unit

Size Limits

ADU Type Maximum Size
Detached ADU 1,000 sq ft or 50% of primary dwelling
Attached ADU 1,000 sq ft or 50% of primary dwelling
Basement Conversion Existing basement footprint

Setbacks

  • Front: Must comply with base zone (typically 25 ft)
  • Side: 5 feet minimum
  • Rear: 5 feet minimum

Height

  • Detached ADU: Maximum 20–25 feet depending on zone
  • Cannot exceed height of primary dwelling

Occupancy Limits

Boulder has residential occupancy limits:

  • Maximum 3 unrelated persons per dwelling unit in most single-family zones
  • Near-CU neighborhoods may have stricter limits
  • These limits apply to the ADU as well as the primary dwelling

Affordable Housing Considerations

Boulder has a mandatory affordable housing program. Long-term ADU rentals may be subject to affordability deed restrictions depending on how the unit is approved and financed.

Parking

One additional off-street parking space required per ADU. In some areas near transit or downtown, parking requirements may be reduced.

Permit Process

  1. Check occupancy limits: Verify residential occupancy limits for your zone
  2. Verify zoning: Contact Boulder Planning & Development Services
  3. Submit plans: Architectural and site plans
  4. Plan review: Zoning and building compliance
  5. Building permit: Issued after approval
  6. Inspections and CO: Required before occupancy

Contact

Boulder Planning & Development Services 1739 Broadway, Boulder, CO 80302 Phone: (303) 441-1880 Website: bouldercolorado.gov/planning-development-services

Disclaimer: Boulder has complex occupancy regulations. Verify all current requirements with Boulder Planning & Development Services before starting any project.

More about Boulder Zoning

Sources

  1. Boulder Revised Code — Land Use Regulations·library.municode.com·Accessed 2026-04-07·Direct link
  2. City of Boulder Planning & Development Services·bouldercolorado.gov·Accessed 2026-04-07·Direct link

FAQ

Are ADUs allowed in Boulder, Colorado?
Yes. Boulder permits accessory dwelling units (called 'accessory units' locally) in residential zones. Boulder has unique occupancy restrictions due to its growth management policies and university population.
What is the maximum ADU size in Boulder?
In Boulder, accessory units are generally limited to 1,000 square feet or 50% of the primary dwelling's floor area. Boulder may have additional restrictions based on lot size.
Does Boulder have special ADU restrictions due to CU Boulder?
Yes. Boulder has Residential Occupancy Limits and special regulations in neighborhoods near the University of Colorado. These may limit the total number of unrelated occupants per dwelling unit.