An Accessory Dwelling Unit (ADU) is an extra living space or secondary dwelling, which can help to house multi-generational families and enables seniors to “age-in-place” with their family. (Photo: Kara Eads, Unsplash).

Across the nation, senior housing facilities, from independent living to memory care, have been hit hard by the coronavirus. As a result, many families are choosing to bring their elderly loved ones into their home. If a loved one needs skilled nursing care, bringing that senior into the family home will not likely be an option. However, if the senior is still fairly independent and just needs a little help, an Accessory Dwelling Unit (ADU) could be just the ticket. An ADU is an extra living space or secondary dwelling, which can help to house multi-generational families and enables seniors to “age-in-place” with their family. Due to the high cost of senior housing, an ADU could also be a very good financial decision.

An ADU is an additional residential unit with separate kitchen, sleeping and bathroom facilities. Rules vary nationally and from community to community regarding how such a unit can be set up. In the city of Boulder, an ADU can either be attached or detached from a principal dwelling on a single-family lot and the owner must live in one of the units. Over the years, the real estate industry has fondly referred to these as “mother-in-law” suites or “granny flats.”

Not all single-family homes create the perfect physical situation for creating an ADU. City of Boulder recognized the need for ADUs many years ago and has provided detailed guidelines. Guidelines vary for attached, detached, Landmarked, or affordable units. As an example, these are the basic requirements listed below for setting up an attached ADU in the city of Boulder

1) Application Process: the owner must fill out an application form provided by the City of Boulder. In addition to the application, the following information is required: Survey or Improvement Location Certificate (ILC); Detached ADUs: Survey must show topography and low point within 25’; Floor Plans of all levels of structure; Building Elevations (Detached ADUs); Project Information Form; Proof of Ownership; Plumbing Fixture Count form; Sign Posting Acknowledgement Form; Application Fee

2) Parking – One off-street parking space for the principal dwelling unit and one off-street space for the ADU

3) Saturation: the number of ADUs are limited to 20 percent within a 300 foot radius.

4) Zoning where ADUs are allowed: ADUs are allowed in the city of Boulder Residential Zones, Rural, Estate, Low and Mixed. ADUs are also allowed in Agricultural and Public Zones.

5) Unit Size: 1/3 of existing floor area or 1,000 square feet, whichever is less

6) Minimum lot size: the minimum lot size is 5,000 square feet.

7) Design: the ADU must be located within the existing single-family dwelling structure.
It must meet the lot size and parking requirements. Interior connections must be maintained. Additional entrances must be screened if facing the street. Must still look like a single-family home. There are more design guidelines on the website.

8) Rental requirements: If the ADU is going to be rented, a City of Boulder Rental License is required.

9) ADU Maximum Occupancy (Directly from the City of Boulder website): the principal dwelling unit and accessory unit together are considered one dwelling unit for the purposes of determining occupancy requirements. For the purposes of ADUs, any occupant and his or her dependents shall be counted as one person. For example, a family may live in the principal home and two unrelated persons may reside in the accessory unit (three unrelated persons in the RMX zoning districts). As mentioned above, any occupant and his or her dependents are considered one person. Therefore, in the example above, a parent with dependent children may occupy the accessory unit plus one unrelated person (two in the RMX zoning districts).

If an ADU is of interest to you and you live in Boulder, see the City of Boulder’s website for details:

For other communities, be sure to consult your local municipality for requirements for creating an ADU.

Be sure to consult your Realtor® for additional advice on how an ADU could affect your property values and more.

By Duane Duggan. Duane has been a Realtor for RE/MAX of Boulder since 1982. Living the life of a Realtor and being immersed in real estate led to the inception of his book, Realtor for Life. For questions, e-mail [email protected], call 303.441.5611 or visit