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Broomfield, CO Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Broomfield, CO, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

ADUs per parcel: One only
Size cap: 50% of house or 800 sf, less of two
Minimum allowed size: Up to 500 sf regardless
Design: Must match principal dwelling
Utilities: Shared with principal dwelling
Recording: Declaration of use required

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Colorado under recent ADU streamlining laws. The Broomfield, CO rules below cover local size, height, and setback requirements.

Summary

Broomfield allows one accessory dwelling unit per parcel in any zoning district that permits single-unit residential use, under Broomfield Municipal Code section 17-32-160. An ADU cannot exceed 50% of the principal dwelling's footprint or 800 square feet, whichever is less, though any owner may still build up to 500 square feet regardless of house size.

Accessory dwelling units are permitted accessory uses in all zoning districts which establish single-unit residential uses as a permitted use, subject to the following conditions: ... (B)Only one accessory dwelling unit shall be allowed for each parcel. ... (D)The square footage of the accessory dwelling unit shall be no larger than 50% of the principal dwelling unit footprint or 800 square feet, whichever is less.; provided, that, in all cases, an accessory dwelling until may be up to 500 square feet in size regardless of the size of the principal dwelling unit. ... (F)To preserve the appearance of the single-unit dwelling and the greater residential community, accessory dwelling units shall be designed in the following manner:i.The design of the accessory dwelling unit shall be consistent with the design of the principal dwelling unit by use of similar architectural style(s), exterior wall material(s) and color(s), window type(s), door and window trim(s), roofing material(s) and roof pitch and color(s).

View official code

Full Breakdown

Section 17-32-160 lets an ADU be located inside, attached to, or detached from the principal single-unit dwelling, but only one is allowed per parcel and a principal dwelling must exist or be built with it. Attached units, and detached units that fall short of the separation distance in section 17-34-020(H), must meet full principal-building setbacks; detached units that clear that separation instead follow accessory-building setbacks, with the side setback capped at whatever the principal building's side setback is and no ADU permitted between the house and the street.

The 50%/800-square-foot size cap excludes garages, porches and similar areas, and every homeowner keeps a 500-square-foot floor regardless of the house's size. Subsection (F) requires the ADU's architectural style, exterior materials, window and door trim, and roofing to match the principal dwelling, with stricter matching where a site development plan or PUD already sets design standards. ADUs must run on the principal dwelling's utility services (except phone, TV, electric and internet), and any septic-served ADU needs Broomfield Department of Public Health and Environment sign-off on capacity.

Home occupations are allowed inside an ADU if they comply with section 17-32-020, and every owner must record a declaration of use stating the ADU's size and location, filed before certificate of occupancy for detached units. Travel trailers, RVs, shipping containers and other temporary structures cannot serve as an ADU. The section was last amended by Ordinance No. 2265, section 2, effective 9-9-2025.

Violations & Fines

Building an ADU larger than the 50%/800-square-foot cap, skipping the required design match to the principal home, or occupying a detached unit without first recording the declaration of use are zoning violations that Broomfield's Department of Community Development can cite and require corrected before occupancy. Using a prohibited temporary structure, such as a shipping container or RV, as an ADU is grounds for permit denial or removal, and a second ADU on the same parcel will be denied outright since only one is allowed.

Frequently Asked Questions

Can I build more than one ADU on my Broomfield lot?

No. Section 17-32-160(B) allows only one accessory dwelling unit per parcel, whether it is attached, built inside the home, or detached, so a second ADU application on the same lot will be denied regardless of the lot's size.

How big can a Broomfield ADU be?

Up to 50% of the principal home's footprint or 800 square feet, whichever is smaller, per section 17-32-160(D). Every homeowner may still build up to 500 square feet even if that exceeds 50% of a small principal home's footprint.

Does a detached ADU have its own setback?

Yes. Detached units generally follow the accessory-building setback in section 17-34-020(H): at least seven and a half feet from the principal home or another accessory building, and never located between the front of the house and the street.

Do I need to record anything before renting out my Broomfield ADU?

Yes. Section 17-32-160(I) requires every owner to record a declaration of use stating the ADU's size and location and confirming it will stay in compliance with the code's accessory dwelling unit rules, filed before a certificate of occupancy for detached units.

Sources & Official References

[1]Broomfield Municipal Code

Other rules in Broomfield

Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Garage ConversionsLight Restrictions ADU Impact FeesSome Restrictions ADU Rental RestrictionsHeavy Restrictions Tiny HomesSome Restrictions Parking Rules: Driveway RulesSome Restrictions Fence Regulations: Material RestrictionsSignificant Restrictions Animal Ordinances: Pet Groomer RulesFew Restrictions Animal Ordinances: Veterinary Clinic ZoningSome Restrictions Fire Regulations: Propane StorageSome Restrictions

All Broomfield rules

How Broomfield compares: Easiest Cities to Build an ADU·Compare Broomfield to another location·View the Colorado accessory structures overview

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