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ADU, Cottage, Granny Unit, carriage house

Accessory Dwelling Units (ADUs)

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Accessory Dwelling Units are also known as a mother-in-law suites, carriage houses, or garage apartments. These are defined as "a second dwelling either within or added to an existing single-family home, or in a separate accessory structure on the same property as the main home, for use as a complete, independent living facility..."

General requirements for ADUs

  • Allowed as an accessory use to a single-family detached home
  • Permitted in residential or mixed-use zoning districts (check the City's Zoning Map to verify zoning for a specific property)
  • The ADU must be subordinate in size to the main home (50% or less of the finished floor area of the principal dwelling)
  • One additional off-street parking space needs to be provided for the ADU
  • The property owner must occupy either the principal or accessory dwelling unit and they cannot be leased or rented for tenancies of less than 30 days. 
  • Mobile homes, recreational vehicles (RVs), tiny homes built on trailers, and travel trailers cannot be used as ADUs.
  • The Site Plan Waiver process is typically used to review and approve requests for ADUs
  • Building permits are required to construct ADUs
  • Fees for ADUs vary depending on the specific project and will be calculated with the building permit. Fees typically range from $5,000 - $10,000 and include plan review and permit fees, City and County taxes, and a number of community investment fees.

The complete, specific development standards are outlined in the Municipal Code's §15.04.040

For questions, contact us at (303) 651-8330 or

Last modified: 10/15/2018,  I. Colby

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