ADU rules in Broomfield

Broomfield has allowed ADUs since 2019 as a permitted accessory use in every zoning district that permits single-unit residential uses, and the unit may be fully detached (a backyard cottage or carriage house). One ADU is allowed per parcel, and a single-unit dwelling must already exist on the lot or be built together with the ADU. Detached ADUs must meet the accessory-building placement standards of BMC 17-34-020(H), including at least 7.5 feet of separation from the principal building, and may not be placed between the front of the principal structure and the street. The side setback for a detached ADU is never larger than the setback required for the principal building on the same lot.

ADUs located within the principal dwelling (for example a basement apartment) or attached to it are expressly allowed in the same districts as detached ADUs. Attached ADUs, and detached ADUs that do not meet the minimum separation distance from the house, must meet the principal-structure setbacks of the zone district. The unit must share the principal dwelling's water and sewer service, and its design must be consistent with the principal dwelling.

Every eligible lot may have an ADU of up to 500 square feet no matter how small the house is. An ADU larger than 500 square feet is limited to 50 percent of the principal dwelling unit's footprint or 800 square feet, whichever is less. Garage, porch, and similar areas are excluded from the square footage calculation for both the principal dwelling and the ADU. There is no ADU-specific height limit; detached units follow the zone district's accessory building standards.

Ordinance No. 2265 (adopted September 9, 2025, effective September 16, 2025) removed Broomfield's former requirement that the owner occupy either the principal home or the ADU, aligning the code with HB24-1152 (C.R.S. 29-35-103(2)(b)), which bars owner-occupancy mandates in subject jurisdictions. The current Sec. 17-32-160 contains no occupancy condition, and the city's ADU page states that any property owner may add one ADU to any eligible property. Owner occupancy still matters for short-term rentals: an STR license is limited to the owner's principal residence, and ADUs cannot be used as short-term rentals at all.

Broomfield's 2025 parking code update (Ordinance No. 2268, May 13, 2025) set the ADU parking minimum at zero. One space is required only when the lot has no existing off-street parking such as a driveway or garage, the adjacent streets do not allow on-street parking, and the property is not within a mapped Parking Reduction Area. The city's ADU FAQ explains that when the exception applies the owner must show three off-street spaces in a garage or driveway, two for the primary dwelling and one for the ADU. This mirrors the narrow exception state law allows under C.R.S. 29-35-103(3)(b).

ADUs are a permitted accessory use, not a special review or conditional use, in every district that permits single-unit residential uses, so approval is administrative with no public hearing. The city processes ADUs through a standard building permit with an ADU checklist submitted to the Building Division. The owner must record a declaration of use stating the ADU's size and location; for detached ADUs the declaration must be recorded before the certificate of occupancy is issued. This administrative path is what HB24-1152 requires of subject jurisdictions.

Nothing in the ADU section restricts leasing the unit for 30 days or more, and since Ordinance No. 2265 neither the ADU nor the principal dwelling must be owner-occupied, so both may be rented long-term. BMC 17-32-160(E) makes ADUs ineligible for use as a short term rental as defined in chapter 5-39 (rental of all or part of a dwelling for under 30 days). Broomfield's STR program (license required, 100 dollar application fee, 5-year license) is itself limited to the property owner's principal residence, and short term rental of a non-principal residence is prohibited under BMC 5-39-050. HB24-1152 expressly preserves local regulation of ADU short-term rentals (C.R.S. 29-35-103(3)(g)), so the ban stands alongside state law.