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Mesa County, CO Accessory Structures: ADU Rules (2026)

Some Restrictions

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

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

Key Facts

ADU per parcel: 1 maximum
Size, under 1/2 acre lot: 900 sq ft max
Size, 1/2 to 1 acre lot: 1,200 sq ft max
Size, 1+ acre lot: 1,500 sq ft or 50% of home
Minimum lot size: 6,500 sq ft
Parking: 1 space per ADU bedroom

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 Mesa County, CO rules below cover local size, height, and setback requirements.

Summary

Mesa County caps accessory dwelling units at 900 square feet on lots under half an acre, 1,200 square feet on lots between half an acre and one acre, and 1,500 square feet, or half the principal home's living area, whichever is larger, on lots of an acre or more, under Section 6.04(E) of the Land Development Code.

These county ordinances apply to unincorporated areas of Mesa County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

a. Only one (1) attached or detached accessory dwelling shall be allowed per parcel or lot. ... (1) On parcels or lots less than one half (1/2) acre in size: A maximum of nine hundred (900) square feet is allowed. (2) On parcels or lots greater than one half (1/2) acre but less than one (1) acre in size: A maximum of one thousand two hundred (1,200) square feet is allowed. (3) On parcels or lots one (1) acre or greater in size: A maximum of one thousand five hundred (1,500) square feet or fifty (50) percent of the heated living area of the principal dwelling whichever is greater.

View official code

Full Breakdown

16(C). Size is measured by the structure's total heated living area, and it scales with lot size: under half an acre the cap is 900 square feet, between half an acre and one acre it rises to 1,200 square feet, and at one acre or larger the ADU may reach 1,500 square feet or 50 percent of the principal dwelling's heated living area, whichever figure is greater. A combination ADU built inside an accessory structure, such as space carved out of a garage, shop, or barn, is measured under the same size table.

Every accessory dwelling must meet the same setbacks as the principal structure, sit on a parcel of at least 6,500 square feet, and provide one off-street parking space per bedroom. 04(E)(2)(g) blocks an ADU on any lot that instead holds a duplex or multi-family building, and the ADU's construction materials and roofline must be complementary to the principal house.

Violations & Fines

Building or occupying an ADU larger than its lot-size cap, or adding a second accessory dwelling on the same parcel, is a Land Development Code violation the Community Development Department enforces under Chapter 11. It can withhold or revoke the Site Plan approval, order the oversized structure altered, and treat each day the violation continues after notice as a separate offense under Section 11.03.

Frequently Asked Questions

Can I build more than one accessory dwelling on my Mesa County property?

No. Section 6.04(E)(2)(a) of the Land Development Code limits every parcel or lot in unincorporated Mesa County to one attached or detached accessory dwelling, whether it stands alone or is built inside an accessory structure like a garage or barn, so a second unit needs a separate parcel.

How is accessory dwelling size measured in Mesa County?

The Land Development Code measures an ADU using the total heated living area of the proposed structure, not overall footprint, and applies that figure against a sliding cap: 900 square feet under half an acre, 1,200 square feet up to one acre, and 1,500 square feet or half the main home's area beyond that.

What is the smallest lot that can have an accessory dwelling in Mesa County?

Section 6.04(E)(2)(f) sets a 6,500-square-foot minimum parcel size for any lot seeking an accessory dwelling, and the lot must already carry a single-family detached home; Section 6.04(E)(2)(g) rules out ADUs on parcels holding a duplex or multi-family building instead.

Sources & Official References

[1]Mesa County Land Development Code § 6.04(E) (Accessory Dwellings)

Other rules in Mesa County

Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingSome Restrictions ADU Rental RestrictionsSignificant Restrictions ADU Owner OccupancySignificant Restrictions Tiny HomesSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Noise Ordinances: Aircraft NoiseSignificant Restrictions Parking Rules: Driveway RulesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Parking Rules: Loading ZonesSome Restrictions

All Mesa County rules

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

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