Building permits, zoning and land rules in Los Alamos County, New Mexico

Los Alamos County requires building permits for covered residential construction and alterations, and work must wait until the permit is issued¹. Starting early can bring double fees and require removal of work for inspection¹. Submitted plans must meet applicable County regulations and adopted codes, including the 2021 building, residential, energy and fire codes; not every code applies to every project¹².

Work must remain accessible and exposed until approved, and cannot proceed beyond a required inspection point without written approval⁶. Covered construction requires a final inspection for a Certificate of Completion or Certificate of Occupancy, depending on the project^1,6. Final state electrical and mechanical inspections must precede the County final inspection⁶.

The Los Alamos County Building Safety Division administers residential building permits; call 505-662-8120, email permit.techs@lacnm.us or visit 1000 Central Avenue, Suite 150, Los Alamos¹. The Planning Division, at the same address and phone number, answers zoning and district questions¹³. Start with the project checklist, prepare the required plans, review the published fees, and submit the application online or in person¹. The County requires 2 sets of building plans and site plans for plan review, and says most residential permits take 3 business days to process¹.

After staff review, the County contacts the applicant if more information is needed; once the application is approved, the permit technician collects the remaining fees and issues the permit¹. Electrical, plumbing and mechanical inspections are performed by the New Mexico Construction Industries Division rather than the County⁶. Keep the work exposed at each required inspection point and arrange the applicable final inspections before requesting the County's final approval⁶.

Los Alamos County Planning administers countywide zoning under Chapter 16 of the Development Code². County Planning can identify a parcel’s zoning district and allowable uses; published Townsite and White Rock maps and the parcel map help locate the property^2,14. Minimum lot size, setbacks, height and density depend on the district, so ask Planning for the applicable district standards before designing a home¹¹.

Accessory dwelling units are permitted in SFR-1, SFR-2, SFR-3, RA, RE, RM and MFR-L, subject to use-specific standards¹¹. Los Alamos County ADUs must contain 250–800 square feet and cannot exceed the primary dwelling’s gross floor area¹⁰. A building permit is required before ADU construction, and base-zone lot, setback, coverage and height standards still apply¹⁰. Subdivision plats receive Planning and Zoning Commission review, while qualifying summary plats may be handled administratively¹⁴.

The New Mexico Environment Department administers septic permits in Los Alamos County⁴. New or modified onsite liquid-waste systems require a paid state permit before construction, except graywater systems meeting the state exemption; other local approvals may also apply⁵. The Santa Fe District Office handles liquid-waste permit questions and permit searches¹⁵.

A homeowner installing a conventional system must pass the NMED qualification exam and may install it only for the homeowner’s personal residence, not a rental or another property⁸. Homeowner installations require a final NMED inspection before covering the system, and the permit may require additional inspections⁸. Before transfer of a property with an established onsite system, the system must be evaluated and the evaluation report submitted to NMED within 15 days⁸.

Only about 2.5% of mapped county soils avoid severe conventional drain-field limitations, making a parcel-specific site evaluation important before buying¹⁶. Where public sewer is available and the local authority requires connection, onsite-system users must connect and properly abandon the old system within 30 days afterward⁵. Cesspools are prohibited, and untreated waste disposal must follow state sanitation rules⁵.

A permanent-foundation tiny house can qualify as a dwelling under New Mexico’s residential code if it provides complete living facilities and meets state tiny-house requirements⁹. Los Alamos County zoning still controls residential use and district standards³. If the tiny home is an accessory dwelling unit, the County’s 250–800-square-foot range applies, and the unit cannot exceed the primary dwelling’s gross floor area¹⁰. That ADU rule does not establish a minimum floor area for every principal dwelling¹⁰.

A tiny house on a chassis with a permanent axle is treated as an RV under the state rule⁹. Los Alamos County prohibits camping, including RV occupancy, on county-owned or county-leased property except designated campgrounds¹⁷. We could not confirm permission for long-term RV occupancy or temporary camping on private land; ask County Planning about the parcel, duration and sanitation before relying on that arrangement¹³. Manufactured-home placement requires a County application packet and compliance with district standards³.

1. Find the parcel on the County map, identify its district, and confirm that the dwelling and any accessory unit are allowed^2,11.
2. Use the district standards to shape the site plan, including the applicable setbacks and height limit¹¹.
3. If the site needs onsite wastewater, obtain state approval before installing or modifying the system⁸.
4. Complete the project checklist and submit the residential application and plans before starting work¹.
5. Pay the plan-review fee when submitting plans and remaining permit fees after approval^1,18.
6. Schedule County and state trade inspections as applicable, leaving work exposed until approval⁶.
7. Pass the final inspection and obtain the applicable Certificate of Completion or Certificate of Occupancy⁶.

Before buying in Los Alamos County, confirm the parcel’s district, allowed residential use, minimum lot size, setbacks and height standards with County Planning^11,14. For an existing septic system, ask the Santa Fe District Office for the permit record and arrange the required pre-transfer evaluation^8,15.

Identify the road authority: constructing or modifying access to a state highway requires a New Mexico Department of Transportation permit¹⁹. Ask the local Floodplain Administrator about special flood hazard areas, where approval is required before covered development²⁰.

Budget separately for planning fees based on project type, building permit fees based on construction value, and applicable water, sewer and electric connection fees¹⁴. The County’s plan-review fee is 65% of the building permit fee and is due with the plans; revisions can add hourly charges¹⁸.