ADU rules by zoning district
Setbacks for a detached ADU, the size limit and maximum lot coverage, from the published code (Mesa County 2020 Land Development Code, Amended 04-23-24 (current adopted PDF on mesacounty.us). A full LDC rewrite (PRO2026-0092, draft Rev. 7-24-26) is pending - see pendingChanges.). The lot check applies the row for your parcel’s district.
| District | ADU allowed | Front | Side | Rear | Lot coverage |
|---|---|---|---|---|---|
| AF-35 Agricultural and Forestry District | Yes | 50 ft | 50 ft | 50 ft | — |
| AFT Agricultural, Forestry, Transitional District | Yes | 50 ft | 10 ft | 30 ft | — |
| RSF-R Residential Single Family - Rural District | Yes | 50 ft | 10 ft | 30 ft | — |
| RSF-E Residential Single Family - Estate District | Yes | 20 ft | 15 ft | 25 ft | 25% |
| URR Urban Residential Reserve District | Yes | 20 ft | 15 ft | 25 ft | 50% |
| RSF-1 Residential Single Family - 1 District | Yes | 20 ft | 15 ft | 30 ft | 20% |
| RSF-2 Residential Single Family - 2 District | Yes | 20 ft | 15 ft | 30 ft | 30% |
| RSF-4 Residential Single Family - 4 District | Yes | 20 ft | 7 ft | 20 ft | 50% |
| RMF-5 Residential Multi Family - 5 District | Yes | 20 ft | 5 ft | 15 ft | 60% |
| RMF-8 Residential Multi Family - 8 District | Yes | 20 ft | 5 ft | 10 ft | 70% |
| RMF-12 Residential Multi Family - 12 District | No | 20 ft | 5 ft | 10 ft | 75% |
| RMF-16 Residential Multi-Family - 16 District | No | 20 ft | 5 ft | 10 ft | 75% |
| RMF-24 Residential Multi-Family - 24 District | No | 20 ft | 5 ft | 10 ft | 80% |
Size limit: By lot size, heated living area: <1/2 ac 900; >1/2 ac and <1 ac 1,200; >=1 ac greater of 1,500 or 50% of principal heated living area . District min lot is 35 acres, so the >=1 acre tier normally applies.
Sources: www.mesacounty.us · www.mesacounty.us · www.mesacounty.us
Questions people ask
Are ADUs allowed in unincorporated Mesa County?
Yes, on single-family lots in the AF-35, AFT, RSF-R, RSF-E, URR, RSF-1, RSF-2, RSF-4, RMF-5 and RMF-8 districts. They aren’t allowed in RMF-12, RMF-16 or RMF-24. One ADU is allowed per lot.
How big can an ADU be in Mesa County?
It depends on the lot: up to 900 square feet of heated living area on lots under half an acre, 1,200 on lots between half an acre and an acre, and on an acre or more the greater of 1,500 square feet or half of the main home’s heated area.
What setbacks apply to an ADU in Mesa County?
Today an ADU must meet the same setbacks as the main house for its district — for example 20 feet from the street, 7 feet from the side and 20 feet from the rear in RSF-4. The county is rewriting its ADU rules to meet a 2024 state law; the proposal moves ADUs to the smaller accessory setbacks.
Is there a minimum lot size for an ADU in Mesa County?
Currently an ADU needs a single-family lot larger than 6,500 square feet. The proposed rewrite removes that minimum.
Does an ADU in Mesa County need parking?
Currently, one off-street space per ADU bedroom. The proposed rewrite deletes the parking requirement.