Building permits, zoning and septic rules in Doña Ana County, New Mexico

Unincorporated Doña Ana County requires a building permit for residential construction, administered by the county's Building Services Division¹. Las Cruces handles building permits inside city limits; onsite wastewater applications still go to NMED's local field office^3,6. State rules require a permit before covered construction begins, although listed exceptions include qualifying one-story detached accessory buildings up to 120 square feet, fences up to 6 feet, and detached decks up to 200 square feet¹⁰. An eligible property owner may obtain a homeowner permit only for the owner's primary residence, must personally complete the major portion of the work by dollar amount, and cannot use that permit for HVAC or gas installations⁸. A homeowner permit does not waive applicable permits or inspections; the application requires zoning approval, a floodplain determination, proof of ownership and fees⁸. The county's building-code fee schedule sets new single-family and duplex construction at $0.20 per square foot of total floor area measured to the outside walls, and work started without a permit costs triple the original permit fee if the investigation shows a permit was required¹¹.

Doña Ana County's Building Services Division coordinates the review and processing of permit applications and works closely with other county departments to confirm each application meets building codes, zoning regulations, and required setbacks¹². The division accepts applications for commercial and residential building, plumbing, mechanical, electrical, and manufactured (mobile) home permits¹². Reach Building Services at (575) 647-7350, by email at buildingservices@donaana.gov, or in person at 845 N Motel Blvd, Las Cruces, NM 88007¹². Doña Ana County lists the 2021 International Residential and Building Codes among its adopted codes; the state framework lists the 2021 New Mexico Residential and Commercial Building Codes^13,14. The state lists 2024 New Mexico Plumbing and Mechanical Codes effective August 1, 2026 with transition provisions, so ask Building Services which edition applies to your project^12,14.

Doña Ana County has zoning in unincorporated areas under its Unified Development Code (UDC), Chapter 350 of the county code, and an Official Zoning Map, so confirm a parcel's district on that map². Las Cruces administers its own zoning inside city limits, while onsite wastewater applications remain with NMED's local field office^4,5. Community Development handles the county UDC, map atlas, GIS and rural addressing¹⁵. Lot sizes, setbacks and building-height limits vary by district; minimum lot area can also depend on access to community sewer or NMED requirements⁷. Manufactured homes are allowed only in districts where the UDC permits them, including the rural residential district described for lots of at least five acres⁷. Accessory dwellings are allowed in some districts and require a special-use permit in others; district rules can limit a lot to one accessory dwelling of no more than 1,800 square feet⁷. Reach Community Development at (575) 647-7350 or 845 N Motel Blvd, Las Cruces, NM 88007 to identify the parcel's district before designing¹⁵.

Onsite wastewater applications in Doña Ana County go to the local New Mexico Environment Department field office; NMED may approve, condition or deny the application⁵. Doña Ana County residents can contact NMED's Las Cruces field office at 2301 Entrada del Sol or 575-288-2050¹⁶. The application package includes owner authorization, proof of ownership, site and floor-plan information and, when applicable, a plat or survey; payment comes after approval, followed by a Permit to Construct⁵. NMED must inspect the system before it is covered, with the request made 48 hours, or two business days, in advance; an approved final inspection leads to a Permit to Operate⁶. Homeowner-installed systems always require an NMED final inspection and may require several inspections during installation¹⁷. About 34.5% of county soils are rated without severe limits for a conventional septic drain field, so evaluate the site before choosing a system¹⁸.

Doña Ana County generally requires travel trailers and recreational vehicles outside approved RV parks to qualify for a temporary-use exception⁷. During construction or remodeling of a home, the owner needs both a valid building permit and a temporary-use permit; the temporary permit lasts six months, may be renewed for another six months while work proceeds, and ends 30 days after the certificate of occupancy⁷. A temporary use lasting more than seven days is limited to one RV per property⁷. In Doña Ana County, a code-compliant tiny house used as one dwelling is defined as 400 square feet or less excluding lofts, must have complete independent living facilities on a permanent foundation, and still needs county zoning, building-permit, septic and floodplain approvals⁹. A tiny house on a permanent-axle chassis is treated as an RV until the axle is removed and the unit is placed on a foundation¹⁹. Manufactured homes are allowed only in county zoning districts that permit them, so confirm the parcel's district with Community Development^7,15.

1. Call Community Development at (575) 647-7350 to confirm your parcel's zoning under the Unified Development Code and any required setbacks before you design anything¹⁵.
2. Ask the Office of the Flood Commission at (575) 525-5558 whether your parcel sits in an area with a 1% or greater annual chance of flooding²⁰.
3. If the site isn't on a public sewer, apply for a liquid-waste permit through NMED's Las Cruces field office at 575-288-2050 with the required ownership and site documents^6,16.
4. Apply for your building permit through Doña Ana County Building Services at (575) 647-7350 or buildingservices@donaana.gov^1,12.
5. Schedule required inspections as construction proceeds; permitted work must pass the required inspections before a certificate of occupancy is issued²¹.
6. Obtain the certificate of occupancy or approved final inspection that applies to the project before occupying the building²¹.
7. If your access road connects to a state highway, get a separate access permit from the New Mexico Department of Transportation before you build or modify it²².

About 78% of Doña Ana County is federal land, so confirm a parcel's ownership and legal access before you get attached to it¹⁸. The county averages 9.9 inches of precipitation a year and experiences severe drought in roughly a third of years, making water rights and well capacity central due-diligence questions¹⁸. About 88% of the land has a slope of 15% or less, but ask the Office of the Flood Commission whether the parcel is in a flood-hazard area^18,20. County subdivision reviews and approvals go through the Planning and Zoning Commission, so confirm that any proposed split or recently divided parcel was properly reviewed²³. New Mexico also regulates land division statewide, subject to statutory exceptions²⁴. A driveway onto a state highway needs an NMDOT access permit before construction or modification²². The typical home value is about $289,376, with a median property-tax bill near $1,404 a year and an effective rate around 0.7%¹⁸.