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Planning & Zoning - Accessory Dwelling Units (ADUs)

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1. What is an Accessory Dwelling Unit (ADU)?

See this informative guide to ADUs

2. Can I put an Accessory Dwelling Unit on my lot?

ADU’s are allowed in all Agricultural (A), Residential (R, MR, SR) and comparable Planned Development (PD) zone districts that allow single family detached dwellings. An ADU may only be allowed as an accessory use to a single family detached residence, so it would not be allowed on a lot which contains a two-family residence, duplex, single family attached residence, townhomes or apartments.

3. Is there a minimum lot size for Accessory Dwelling Units?

This depends on whether the ADU is attached to the primary unit or detached. For attached units, the minimum lot size is the minimum lot size of the underlying zone district. For detached units, the minimum lot size is 7,500 square feet. Therefore, if a lot that is 4,000 square feet in size and that corresponds with the minimum allowed by the zoning, an attached ADU may be constructed, but not a detached ADU.

4. Can I put an Accessory Dwelling Unit above my garage?

This depends on the height of the primary residence. The height of the ADU may not be more than the height of the primary residence or 25 feet, whichever is less. This is so that an ADU stays in character with the lot and the neighborhood.

5. How large can my Accessory Dwelling Unit be?

This depends on whether the ADU is attached to the primary unit or detached.

For attached units, the ADU may be 1200 sf or 40% of the primary unit, whichever is less.

For detached units it depends on the lot size. For lots 1 acre or more, the ADU may be 1200 sf or 40% of the primary unit, whichever is less. For between 12,500 square feet and just less than 1 acre, the ADU may be 800 sf or 40% of the primary unit, whichever is less. For lots between 7,500 square feet and 12,499 square feet, the ADU may be 600 sf or 40% of the primary unit, whichever is less.

6. May I list my Accessory Dwelling Unit on AirBNB?

No, ADU’s may not be used for rentals of less than 30 days.

7. May I rent my Accessory Dwelling Unit?

Yes, as long as the rental is for 30 consecutive days or more.

8. May I live in the Accessory Dwelling Unit and rent my home?

Yes, as long as the rental is for 30 consecutive days or more.

9. May I rent both the Accessory Dwelling Unit and the primary home?

No, the owner of the property must live in either the primary home or ADU.

10. Can I sell the Accessory Dwelling Unit separately from the primary home?

No, the ADU may not be sold separately from the primary home, unless the applicant goes through the County Subdivision process.

11. How many people may live in the Accessory Dwelling Unit?

Up to 3 people may live in the ADU. Additionally, no more than 6 unrelated individuals may live on the property, including the primary home and the ADU.

12. Do you have a guide that talks more about Accessory Dwelling Unit’s and the criteria that applies?

Yes, that document may be found here.

13. My property is in a city, are the regulations different?

Yes, the incorporated Cities in Jefferson County regulate their own zoning, so you will need to check with the City to determine if ADU’s are allowed and what the standards are.

14. My property is on a well and septic, can I have an Accessory Dwelling Unit?

The well permit needs to have the rights to serve more than one dwelling. This information may be found on the well permit. Well permits may be obtained by contacting the Colorado Division of Water Resources at 303-866-3587.

The septic permit will need to be sized to allow for the overall number of bedrooms in both the primary unit and the ADU. For more information on septic permits, contact Jefferson County Public Health at 303-271-5700.

15. Can I have more than one (1) Accessory Dwelling Unit on my property?

No, only one ADU is allowed per property.

16. Can I use a tiny home as an Accessory Dwelling Unit?

If the tiny home meets all Jefferson County’s requirement for a single family home, which includes placing it on a permanent foundation, then yes. If it is a tiny home trailer with wheels, then no. See the FAQ for tiny homes for more information.

17. To have the Accessory Dwelling Unit approved does the application need to go to a hearing?

No, as long as the criteria for the ADU is met, then no hearings are required. Only a Building Permit application is needed.