In this guide
There is a sentence about Earthships that gets repeated everywhere, including in the earlier version of this article, and it is wrong: that New Mexico passed a law making them legal.
What New Mexico actually passed, in 2007, is the Sustainable Development Testing Site Act. It lets a county planning commission designate a site of two acres or less, wholly outside a municipality's platting jurisdiction, for sustainable development research, meaning activities that test ideas, concepts or inventions. The permit runs five years, renewable once and never again. The applicant posts a $100,000 surety. And what it exempts you from is only the county codes and ordinances specifically named in the permit. It expressly does not exempt you from the State Engineer, the Environment Department, or any other state or federal agency, and it says new water appropriations shall in no event be exempted from state water law.
Two acres. Ten years maximum. A hundred thousand dollars of surety. County ordinances only. Framed as research rather than housing. That is not legalisation, and Taos County's own implementation of it requires a reclamation plan showing how the site will be restored to its original state.
So if you are buying ground in northern New Mexico with an Earthship in mind, the useful article is not about tires. It is about what you actually submit, what the water rules allow, and what the arithmetic says about rain. Here it is.
What an Earthship actually is, in buildable terms
Strip the marketing and the building has five defining parts. Load-bearing walls made by compacting earth into used car tires and then rendering them with adobe. A berm of earth against those walls acting as thermal mass, with insulation placed outboard of the tires in the modern design. An attached angled double-glazed greenhouse on the south face working as both thermal buffer and air intake. Rainwater collection with the same water used several times over. And onsite power and sewage treatment rather than connections.
That description is from the peer-reviewed simulation literature rather than from anyone selling one, which matters, because independent testing of the thermal claims is thinner than you would expect from a forty-year-old building type.
What exists is one monitored field study of a single two-bedroom Taos Earthship, completed in 2010 and monitored from January to July 2012. Indoor temperatures held between about 63 and 76 degrees Fahrenheit while outdoor temperatures ranged from 6 degrees to 93. That is a real and encouraging result. It is also one house, seven months, and not a full winter, and the same research group's simulation work found the standard model failing comfort targets in cooler and cloudier climates. No federal laboratory and no New Mexico agency has evaluated Earthship thermal performance.
Worth sizing the climate against the claim. The New Mexico energy code's own table puts Taos at 6,967 feet elevation with 6,827 heating degree days, in climate zone 5B. That is a heating climate comparable to Chicago. The zero-backup-heating claim is being made in Chicago weather on the strength of one seven-month dataset.
The permit, step by step
Assume you are building on an ordinary New Mexico parcel rather than inside a two-acre research site, because almost everybody is. Here is the path.
New Mexico adopted the 2021 International Residential Code as its residential building code, mandatory for permits after December 2023. But New Mexico deletes the code section that normally carries the alternative-materials provision and redirects it to state rule instead, which means the familiar code paragraph people cite for alternative construction does not exist here. The path is a state one: the trade bureau chief is authorised to permit a variance or approve an alternative material or method of construction, no variance is valid unless issued in writing and signed by the chief, and the chief may require supporting data from the requestor.
That is discretionary approval by a named state official, in writing, on a case by case basis. It is not a checkbox.
New Mexico does have a prescriptive earthen building code, and reading it tells you exactly where tires sit. It controls the design and construction of one and two family dwellings where earthen materials form the bearing wall system, and it covers adobe, burned adobe, compressed earth block, rammed earth and terrón. Tires are not mentioned. Rammed earth in a form has a prescriptive path. Rammed earth in a tire does not.
Then Taos County, whose building permit application is the most concrete answer available. When alternative methods and materials are proposed, plans must be designed and sealed by a New Mexico licensed architect or engineer, and a certification for alternative methods and materials form must be submitted. Note what else it says: it is the applicant's responsibility to ensure the certification is recorded with the Taos County Clerk's office before submittal. Recorded against the title. Two sets of plans, a seal signed and dated on every page, energy calculations complying with the state energy code, and mechanical, plumbing and electrical plans approved by the state construction bureaus before the county application goes in.
A single-family dwelling on rural Taos County land also needs a residential zoning clearance, and the county allows no waiver of the performance standards for one. The submittal list includes the deed, proof that all county taxes and code-violation penalties are current, evidence of notifications to and approvals from other entities including acequia associations where applicable, verification that the site is a buildable lot with adequate legal access from a public road, and a site plan describing the proposed wastewater system with leach field location and size and the source and capacity of the water supply.
The contained botanical cell has a route, and it is the expensive one. New Mexico treats a system using treatment technology not fully proven in the circumstances of its intended use as an experimental system. The permitting rule requires review by the state's wastewater technical advisory committee, a field demonstration with department-approved monitoring, on-site testing and evaluation paid for by the applicant for a period the committee sets, a contingency plan providing compliant treatment if the system fails, and a signed maintenance contract with a certified provider in effect for the duration of the permit. Final approval is at the secretary's discretion.
Composting toilets are allowed if certified to the relevant standards, with two conditions worth knowing: installing one does not reduce the design flow required for the liquid waste system, and they may not be used on a lot smaller than three quarters of an acre.
The water arithmetic, which settles the question
Taos averages 12.35 inches of precipitation a year, and it is monsoon-weighted: July through September is 4.77 inches, 39 percent of the annual total. The record range at that station runs from 6.39 inches in the driest usable year to 22.73 in the wettest.
Run the standard formula. Roof area times rainfall times 0.623 gallons per square foot per inch times collection efficiency. A 1,500 square foot roof at 12.35 inches and 80 percent efficiency yields about 9,233 gallons a year, which is 25.3 gallons a day averaged across the year and arriving in bursts. In the driest year on record that drops to 4,777 gallons, or 13 gallons a day.
EPA, citing USGS, puts average American household use at 82 gallons per person per day. One person at that rate needs 29,930 gallons a year, so the 1,500 square foot roof supplies about 31 percent of it. Two people, about 15 percent. To supply one person at the American average on catchment alone you would need roughly a 4,900 square foot roof.
For scale on the alternative, a standard New Mexico domestic well permit allows one acre-foot a year, which is 325,851 gallons, about 35 times what that roof catches.
None of which means catchment is pointless. It means catchment in Taos is a real irrigation and flush supply and a meaningful supplement, and living on it alone means living at roughly a quarter to a third of ordinary American consumption. That is precisely what the design intends. It is a trade-off rather than a free lunch, and the honest version names it.
On wells, New Mexico is unusual. It is not an exemption state: you apply, and the State Engineer shall issue a permit for household use and up to one acre of noncommercial trees, lawn or garden. Issuance is mandatory. The volume cap comes from rule rather than statute, at one acre-foot a year for a single household. The caveat is domestic well management areas, which the State Engineer may declare over a stream-connected aquifer and inside which new permits are generally limited to a quarter of an acre-foot. We could not confirm whether any part of Taos County sits inside one, so ask the State Engineer's Taos district office about your specific parcel before you buy.
Money, financing and the part nobody writes about
There is no independent cost study of Earthship construction. None. The figures in circulation trace back to the builder, reported secondhand: a smaller model at $200,000 to $275,000 for 1,200 square feet, which is $167 to $229 a square foot, and a larger model at upwards of $600,000. The one independent data point we could find is a 1997 owner's account of paying $290,000 for 2,500 unfinished square feet plus $20,000 to $30,000 out of pocket to finish it. The free-from-garbage framing has no verified cost basis behind it.
New Mexico does have a genuine owner-builder exemption from contractor licensing for someone building a single-family dwelling they own and will occupy. Taos County's homeowner permit attaches a condition the statute does not: the applicant initials an acknowledgement that they cannot rent or sell the property after a certificate of occupancy is issued, with denial of future permits or unlicensed-contracting charges as the stated consequence. The certificate of occupancy itself will state the home was built under a homeowner's permit. Read that paragraph twice before you choose the owner-build route.
| Claim you will read online | What the rules actually say |
|---|---|
| New Mexico legalized Earthships | A two-acre research permit, five years renewable once, $100,000 surety, county ordinances only |
| The Taos community is a testing site | A 630-acre platted subdivision of about 130 lots, which the two-acre cap excludes |
| Earthships are exempt from the building code | Alternative method approved in writing by a state trade bureau chief, sealed design required |
| The earthen building code covers tire walls | It covers adobe, burned adobe, compressed earth block, rammed earth and terrón. Not tires |
| You don't need a septic system | A conventional system sized for combined blackwater and greywater flow is still required |
| Greywater can flush the toilet | Not under the 250 gallon exemption. That use needs a department permit |
| You can't finance one | Fannie Mae names earth houses as eligible. Appraisal support and utilities are the real obstacles |
That last row deserves correcting properly, because the claim that an Earthship cannot be financed is overstated. Fannie Mae's selling guide states that loans secured by unique or nontraditional types of housing, including earth houses, geodesic domes and log houses, are eligible provided the appraiser has adequate information to develop a reliable opinion of market value, and that comparables need not be of the same design and appeal. A property is ineligible only where the appraiser can find no evidence of market acceptance at all.
The actual obstacle is elsewhere in the same guide: for a loan to be eligible, the utilities of the property must meet community standards, and where public water and sewer are unavailable, private well and septic facilities must be available and used. So the thing that kills financing is an off-grid house on a cistern with no permitted conventional water source, not the tires. A permitted domestic well and a permitted septic system flip most of it.
Resale is the honest gap. There is no study, no market analysis, no days-on-market dataset and no appraisal paper on Earthship resale. Individual listings exist and asking prices are not sales. Anybody quoting you a resale figure for this building type is making it up. We said something similar about an adjacent category in what the category decides about tiny homes.
One more regulatory exposure nobody mentions
New Mexico's scrap tire rule says a person shall not store or use in a civil engineering application, except for beneficial agricultural use, more than one hundred scrap tires anywhere in the state without a valid department permit or registration. A typical Earthship uses several hundred to roughly a thousand. The listed exclusions cover retail tire dealers, retreaders, permitted solid waste facilities and agricultural use on a farm or ranch. There is no construction exemption in the text. Separately, each shipment of ten or more scrap tires transported in New Mexico must be accompanied by a manifest.
We want to be careful here: we found no guidance, determination letter or enforcement record showing whether the state applies that hundred-tire threshold to someone building a house. The rule text has no exemption, and whether it is enforced that way is unknown. Ask the Environment Department's solid waste bureau before you have 800 tires delivered, not after.
On the materials themselves, the best available evidence is reassuring with caveats. EPA's literature review of tire-derived aggregate found it unlikely to cause exceedances of primary drinking water standards, with iron and manganese potentially increasing in water in direct contact but showing limited ability to migrate away, and organics generally below reporting limits. Nobody has measured indoor air offgassing from rammed-earth-filled tires behind adobe render in an occupied house. We are not going to tell you it is safe or unsafe. We are telling you it has not been measured.
The order to work through it
The order to work through it
Decide whether you are building a house or running a research project.
The testing site permit is the second one, capped at two acres and ten years, with a reclamation plan. Almost everybody wants the first one.
Call Taos County planning with the parcel number before you buy.
Ask what a residential zoning clearance requires on that parcel and what the alternative methods and materials certification involves, including the recording step.
Line up a New Mexico licensed architect or engineer early.
Tire walls are an alternative method, so a sealed design is not optional and the state trade bureau chief approves it in writing at his discretion.
Ask the State Engineer's Taos district office about the well before anything else.
Issuance is mandatory for domestic use, but the volume is capped by rule and a domestic well management area would cut it further. This is a five-minute phone call.
Price a full conventional septic system into the budget regardless of the water loop.
New Mexico requires it sized for combined flow, and a composting toilet does not reduce the design flow.
Do the rainfall arithmetic for your own roof before you plan to live on catchment.
Roof area times inches times 0.623 times 0.8. In Taos that is about six gallons per square foot of roof per year.
Get a written insurance quote before closing, not after.
Nobody publishes anything authoritative on insuring tire-wall or earth-sheltered construction, which means the only way to find out is to ask a carrier in writing.
Where we fit
We sell owner-financed rural land in New Mexico, and some of our buyers are thinking about alternative construction. What we will do is give you the parcel number and the county so you can make the planning call and the State Engineer call yourself, before you commit to ground that may not support the plan.
What we will not do is tell you a parcel is suitable for an Earthship. That depends on a discretionary state approval, a sealed design, a well permit, a septic design and a county clerk recording, none of which we control and none of which we have obtained. The broader version of the permission question is in the guide to living off the grid, and the catchment side is in what each state allows on water catchment.
If northern New Mexico is where you want to be, start with our New Mexico land listings and our off-grid land listings, and make the two phone calls before you fall for the light.
The building is genuinely interesting and the design argument is serious. What has never been serious is the way it gets written about, as though forty years of photographs settle questions that are decided by a trade bureau chief, a soil evaluation and a rainfall average.
If you want to build one, build one. Just buy the ground knowing which approvals it needs, how much water actually lands on it, and that the septic system is going in either way.
