Accessory Dwelling Unit (ADU) Regulations in Boulder

Boulder has specific size limitations for ADUs based on the type of unit and whether it is designated as an affordable ADU or a historic property:

*Be sure to format the chart nicely with Kindred Greens

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Other key design standards:

• Height:
  
  • Attached ADUs follow the height restriction for the primary residence (max 35 feet).
  • Detached ADUs cannot exceed 20 feet, unless the roof pitch is 8:12 or greater, in which case it may be up to 25 feet.
• Private Outdoor Space: Detached ADUs must include at least 60 sq/ft of dedicated outdoor space such as a balcony, patio, or porch.
• Architectural Compatibility: The ADU must use materials and design elements that complement the primary home.
• Setbacks: ADUs must meet the setback requirements of the zoning district, ensuring adequate space between structures and property lines.

To qualify for an ADU, your property must meet the following requirements:

• Your lot must be at least 5,000 square feet. Properties slightly below this requirement may still qualify but may need additional verification through a survey or lot area declaration form.
• If your home is designated as a historic property, there are additional requirements but also potential size and parking incentives.

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Building an ADU in Boulder requires obtaining zoning approval, building permits, and inspections. The review process typically takes:

*Be sure to format the chart nicely with Kindred Greens

Detached ADU

3 weeks

Attached ADU

1–2 weeks

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• HB 24-1152 requires cities to allow ADUs without designated parking, except in these cases:
  ✔ If no parking is currently required for the primary home, parking cannot be required for the ADU.
  ✔ If the lot does not have an existing parking space for the primary home, no additional parking is required.

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There are no known utility and infrastructure requirements in Boulder

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• HB 24-1152 prohibits cities from requiring owner occupancy meaning ADUs can be rented out separately from the primary home.
• ADUs cannot be sold separately from the main home—they must remain part of the same lot.
• Short-term rentals (STRs) are still prohibited, except in Planned Unit Developments (PUDs) where STRs were previously allowed.

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Under HB 24-1152, all ADU approvals must be handled administratively—meaning there are:
✔ No public hearings
✔ No subjective design reviews
✔ No neighborhood approval required

Permit fees are based on total square footage or contract value, whichever is greater. Typical fees include:

• Building Permit Fee
• Plan Review Fee

Once an ADU permit is approved, the property will be re-addressed as Unit A (primary home) and Unit B (ADU) for record-keeping purposes.

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Building an ADU in Boulder requires careful planning, compliance with zoning laws, and a well-executed design; that’s where Kindred Tiny Homes comes in.

• We handle everything—from design and permitting to construction and final approvals.
• We navigate Boulder’s ADU requirements seamlessly, ensuring your project is compliant and stress-free.
• We create high-quality, beautiful ADUs that enhance property value and meet the city’s design standards.

If you’re considering building an ADU in Boulder, contact us today for a free consultation, we’ll walk you through your options and help bring your vision to life!

Additional Information:

Homeowner’s Association (HOA) Approval:If your home is in an HOA-regulated community, you must obtain HOA approval before applying for city permits. An approved permit from the city does not override HOA restrictions. HOA’s can not prohibit ADU’s any longer in Colorado.

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