Accessory Dwelling Units (ADUs)

The following are the requirements to meet the zoning code for an Accessory Dwelling Unit:

• Only one ADU allowed per lot on a single-family dwelling lot
• Cannot exceed 75% of the floor area of the principal unit or 1000sf, whichever is less. 750sf is permitted regardless of the size of the principal units
• Water, sanitary service and electrical utilities shall not be separately provided to an ADU
• The address of the principal dwelling shall remain the same and the ADU shall be assigned a Unit designation
• Vehicular access shall not serve the ADU separate from that serving the principal dwelling unless the accessory dwelling is accessed from an alley and the principal dwelling is accessed from the street
• The detached ADU shall be sited so that the front wall of the ADU is located behind the rear wall of the principal building
• Must be less than the height of the principal building or 22' max; whichever is less
• SETBACKS FROM PROPERTY LINES
• • Front: Same as the principal building setback
  • 5ft side setback
  • 5ft rear setback
  • Side on Street: Same as the principal building setback

• The detached ADU shall be sited so that the front wall of the ADU is located behind the rear wall of the principal building 

For more information on the zoning requirements please contact The Planner of the Day at 303-227-8777 or cdplanner@c3gov.com.

Before submitting an ADU application, property owners must contact the city’s GIS Department to obtain a unit designation for the new unit. The address of the principal dwelling shall remain the same and the ADU shall be assigned a unit designation.

A unit designation is the official way the ADU is identified within the City’s mapping, addressing, and record-keeping systems (for example, assigning a unit letter or number). This step is important because it ensures the ADU can be accurately tracked for permits, inspections, utilities, and emergency response, and that it is correctly associated with the primary residence in city records. Having a unit designation in place upfront helps prevent delays later in the review and permitting process.

Please contact the GIS department at GIS@c3gov.com to obtain a unit designationn.

The following code requirements are based on the Internation Residential Code. This list is not all inclusive of all code requirements that will need to be met.

• If your building project provides for a separate living space that includes a kitchen (with a stove top or oven), a full bathroom, and a bedroom together in the same space, you’ll need to follow specific ADU rules

• The path of egress travel from an ADU to a public right of way or to a yard or court that opens to a public right of way shall be independent of, and not pass through, the primary dwelling unit
• Adjoining ADU's require a 1-hour fire-resistance-rated wall and floor assembly unless both the following conditions are met:
• • The interconnection of smoke alarms per Section R310.4 activates the smoke alarms in both the primary dwelling unit and the ADU
  • The interconnection of carbon monoxide alarms per Section 311.5 activates the carbon monoxide alarms in the primary dwelling unit and the ADU
• ADU shall be provided with a separate heating system, separate ducting for heating and cooling systems and separate climate controls
• ADU shall have ready access to the service disconnecting means serving the dwelling unit
• ADU shall have ready access for each occupant to all overcurrent devices protecting the conductors supplying the swelling unit
• ADU shall have ready access for each occupant to shutoff valves serving the dwelling unit
• ADU shall have ready access for each occupant to appliance shutoff valves serving appliances in the dwelling unit
• A primary dwelling unit and an ADU may share a common potable water system, provided that there are separate, accessible main shutoff valves allowing the water to be turned off on one side without affecting the other

This information is the most common and is not representative of all the design and submission requirements you may encounter.

• Applicable building and electrical codes. See current codes.
• Plans designed for Local Design Criteria
• Foundation plan and footing details (only if new construction)
• Basement wall design
• Floor plans of all levels showing room functions, dimensions, hallway widths and window/door locations
• Bathroom plan showing location of fixtures and associated clearances.
• Thickness of slabs-on-grade, gravel base and vapor barrier (only if new construction)
• Location of smoke and carbon monoxide alarms
• Location of exhaust fans
• Roof/attic ventilation (only if new construction)
• Structural details of connections
• Typical wall section to include sheathing thickness and type
• Stairway tread, riser and landing location and dimensions
• Guard and handrail locations and dimensions
• Insulation R-values, U-factors of all fenestrations. Learn more about Energy Conservation for Residential Projects.
• Roof framing plan indicating the size and spacing of the following as applicable: trusses, rafters, ceiling joists/rafter ties, ridge board, ridge beam and overbuild (only if new construction)
• Enhanced exterior elevations (front, side and rear) noting window and door dimensions and locations, including, separate egress for ADU
• Building cross sections with all posts, joists and beams labeled and ceiling heights shown
• Building height
• Clearance to combustibles for fireplaces
• Emergency escape and rescue opening and associated area well dimensions when applicable for all sleeping areas and basement
• Fire Resistive Rated Construction Details, if applicable
• Energy Documentation and Manual J, D & S (only for new detached and attached construction)
• Power and lighting plans