Accessory Dwelling Units (ADUs)

• Floodplain restrictions: No new units are allowed in the Poudre River 100-year floodplain. Check if your property is in a floodplain here.
• Primary dwelling requirement: You need—or must be allowed to build—a house, duplex or triplex on your lot.
• How many ADUs you can add to your property:
• • Most properties may add one ADU only.
  • In some zones (RUL, RF, CC, CCN, CCR, CG, CS, CL, LMN, MMN, HMN, NC, D, HC, E, I, RC) you may be able to build a second detached house on the lot. You'll still need to meet all the usual development standards.

Check your zoning here.

Size:

Detached ADUs:

• Up to 750 square feet if your main home is smaller than 1,667 square feet
• Up to 1,000 square feet or 45% of the main home (whichever is less) if larger.
• Existing accessory buildings may be converted up to 800 square feet

Attached ADUs:

• Above grade: up to 750 square feet or 45% of the main home.
• Basement: up to 750 square feet or 100% of that floor.

Height:

Detached ADUs may not exceed the height of the main building or the maximum allowed in your zone.

Location:

• Detached ADUs must be behind the front wall of the home.
• Must be at least 5 feet from other buildings (more if special building requirements for fire prevention can’t be met).
• Must follow setback rules for your zone.

Access and Safety:

• A walkway must connect the ADU’s main door to the street.
• The ADU’s address must be visible from the street.

Parking:

No extra parking is required beyond what your main home already needs.

• Houses need one off-street parking space if the lot is wider than 40 feet. Houses need two off-street parking spaces if the lot is less than 40 feet wide.
• Duplexes need one off-street parking space per unit that has one or two bedrooms. Duplexes need two off-street parking spaces if they have three or more bedrooms.

• Utilities: ADUs need their own electric meter. In some cases, you may need to upgrade nearby transformers or pay for trenching.
• Separations: Utility lines, trees, and landscaping must follow spacing rules:
  • 10 feet between water and sewer lines
  • 10 feet between storm drains and other utilities
  • 6 feet between trees and water or sewer lines
  • 4 feet between shrubs and water or sewer lines
• Stormwater: If your project creates more than 1,000 square feet of new impervious surface (roof, pavement), you’ll need stormwater quality treatment such as rain gardens or permeable pavers.
• Trees: Keep new trees and shrubs away from utility lines and vaults.

Building an ADU involves multiple fees, including:

• Basic Development Review: Flat fee of $6,925 (mandatory for ADU projects)
• Utility fees: Water, sewer and electric capacity charges
• Transportation fees: Larimer County road impact and City capital expansion fees
• Building permit fees: Based on project value and other project specifics 

Total fees for ADU developments may be in the range of $20,000-$25,000.

Before you apply, you can meet with City staff through a free Conceptual Design Review.

This lets you:

• Share your ADU idea.
• Learn about potential costs, utility connections and site-specific issues.
• Get feedback before submitting a formal application.

Apply for a Conceptual Design Review here.

All ADUs go through a Basic Development Review.

• Your project is reviewed by multiple City departments (Planning, Utilities, Fire, Stormwater, etc.).
• The decision is made by the Planning Manager or Community Development Director.
• No neighborhood meeting is required, but notice will be posted or mailed.
• All submitted plans become public records.

Learn about the Development Review process here.

After Development Review approval, you'll need a building permit.

Building Code requirements for ADUs include:

• Fire-rated separation between units (for attached ADUs).
• Separate heating systems (for attached ADUs).
• Minimum standards for kitchens and bathrooms.
• Separate exit doors.

Apply for a building permit here. 

Once your permits are issued you can move forward with construction. Be sure to follow approved plans and City inspections throughout the process.