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

At a glance

Building permit

Required in unincorporated Doña Ana County, issued by Building Services¹

Zoning

Yes in unincorporated areas, under the Unified Development Code⁸

Septic permit

State permit through NMED's Liquid Waste Program, not the county⁵

Owner-builder exemption

Available for an eligible owner's primary residence, with state limits⁹

Tiny home on a foundation

A code-compliant dwelling up to 400 sq ft excluding lofts; county approvals still apply¹⁰

RV living

Generally limited to approved parks; temporary use during permitted home construction requires county approval⁷

Lot size and setbacks

Both vary by zoning district; sewer availability can also affect minimum lot area¹¹¹²

Who to call

Contact details are copied from each office’s official page and were checked against it on October 11, 2026.

Do you need a building permit 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 office³¹³. 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 feet¹⁴. 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 installations⁹. A homeowner permit does not waive applicable permits or inspections; the application requires zoning approval, a floodplain determination, proof of ownership and fees¹⁵. 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 required¹⁶.

Who is the Doña Ana County building department, and how do you reach them?

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 setbacks¹⁷. The division accepts applications for commercial and residential building, plumbing, mechanical, electrical, and manufactured (mobile) home permits¹⁷. Reach Building Services at (575) 647-7350, by email at buildingservices@donaana.gov, or in person at 845 N Motel Blvd, Las Cruces, NM 88007¹⁷. 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 Codes¹⁸¹⁹. 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 project²⁰¹⁷.

Does Doña Ana County have zoning?

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 office⁴⁵. Community Development handles the county UDC, map atlas, GIS and rural addressing²¹. Lot sizes, setbacks and building-height limits vary by district; minimum lot area can also depend on access to community sewer or NMED requirements¹¹¹²²². Manufactured homes are allowed only in districts where the UDC permits them, including the rural residential district described for lots of at least five acres²³. 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 feet²⁴. Reach Community Development at (575) 647-7350 or 845 N Motel Blvd, Las Cruces, NM 88007 to identify the parcel's district before designing²¹.

How do septic permits work in Doña Ana County?

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 575-288-2050²⁵. 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 Construct²⁶. 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 installation²⁷. About 34.5% of county soils are rated without severe limits for a conventional septic drain field, so evaluate the site before choosing a system²⁸.

Can you live in an RV or tiny home on your land in Doña Ana County?

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 approvals¹⁰. 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 foundation²⁹. Manufactured homes are allowed only in county zoning districts that permit them, so confirm the parcel's district with Community Development²³²¹.

What are the steps to build a home in Doña Ana County?

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 anything²¹.
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 flooding³⁰.
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 documents²⁵³¹.
4. Apply for your building permit through Doña Ana County Building Services at (575) 647-7350 or buildingservices@donaana.gov¹⁷¹.
5. Schedule required inspections as construction proceeds; permitted work must pass the required inspections before a certificate of occupancy is issued³².
6. Obtain the certificate of occupancy or approved final inspection that applies to the project before occupying the building³³.
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 it³⁴.

What should you check before buying land in Doña Ana County?

About 78% of Doña Ana County is federal land, so confirm a parcel's ownership and legal access before you get attached to it³⁵. 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 questions³⁶³⁷. 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 area³⁸³⁰. County subdivision reviews and approvals go through the Planning and Zoning Commission, so confirm that any proposed split or recently divided parcel was properly reviewed³⁹. New Mexico also regulates land division statewide, subject to statutory exceptions⁴⁰. A driveway onto a state highway needs an NMDOT access permit before construction or modification³⁴. 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%⁴¹⁴²⁴³.

Watch-outs

• A building-permit exemption does not necessarily waive separate plumbing, electrical or mechanical permits, so confirm the complete permit set with Building Services¹⁴¹⁷.
• An RV used during home construction needs both a valid building permit and a temporary-use permit, and the county time limit continues to apply while the project proceeds⁷.
• We could not confirm a general agricultural building exemption or approval of off-grid sanitation methods in Doña Ana County; ask Building Services about agricultural buildings and NMED about your sanitation design¹⁷²⁵.

Sources

1. Doña Ana County Building Services - Permit Requirements (2026 county census)
2. UDC / Land Use Regulations, quoted and re-checked
3. Las Cruces: Permits, Licenses, and Registrations - The City of Las Cruces (Doña Ana County), quoted and re-checked
4. Las Cruces: Community Development - The City of Las Cruces (Doña Ana County), quoted and re-checked
5. Liquid Waste Permitting Process, quoted and re-checked
6. Apply for a Permit, quoted and re-checked
7. ecode360.com, quoted and re-checked
8. UDC / Land Use Regulations (2026 county census)
9. 14.5.2 NMAC Permits, quoted and re-checked
10. 14.7.3 NMAC — New Mexico Residential Building Code, quoted and re-checked
11. Article V: Zoning Districts and Requirements - Doña Ana County, NM, quoted and re-checked
12. Article V: Zoning Districts and Requirements - Doña Ana County, NM, quoted and re-checked
13. Apply for a Permit, quoted and re-checked
14. Building Permit Guide for Residential Construction (New Mexico statewide rule), quoted and re-checked
15. 14.5.2 NMAC Permits, quoted and re-checked
16. Article VI: Building Code Fees, quoted and re-checked
17. Doña Ana County Building Services Division (donaana.gov)
18. Building Codes, quoted and re-checked
19. Rules, Laws, and Building Codes, quoted and re-checked
20. Rules, Laws, and Building Codes, quoted and re-checked
21. Doña Ana County Community Development (donaana.gov)
22. Article V: Zoning Districts and Requirements - Doña Ana County, NM, quoted and re-checked
23. Article V: Zoning Districts and Requirements - Doña Ana County, NM, quoted and re-checked
24. Article V: Zoning Districts and Requirements - Doña Ana County, NM, quoted and re-checked
25. New Mexico Environment Department - Las Cruces Field Office (env.nm.gov)
26. Liquid Waste Permitting Process, quoted and re-checked
27. Homeowners Information, quoted and re-checked
28. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
29. 14.7.3 NMAC — 2021 New Mexico Residential Building Code (New Mexico statewide rule), quoted and re-checked
30. Doña Ana County Office of the Flood Commission (donaana.gov)
31. Apply for a Permit, quoted and re-checked
32. 14.5.3 NMAC Inspections, quoted and re-checked
33. 14.5.3 NMAC Inspections, quoted and re-checked
34. 18.31.6 NMAC (New Mexico statewide rule), quoted and re-checked
35. Federal land share: Bolthole Index county data
36. Annual precipitation: Bolthole Index county data
37. Share of years in severe drought: Bolthole Index county data
38. Share of land at 15% slope or less: Bolthole Index county data
39. Planning and Zoning Commission, quoted and re-checked
40. Senate Bill 176 — New Mexico Subdivision Act (New Mexico statewide rule), quoted and re-checked
41. Typical home value (Zillow): Bolthole Index county data
42. Median property tax bill: Bolthole Index county data
43. Effective property tax rate: Bolthole Index county data

Written October 11, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.