Eco homes on the Oaxacan coast do not begin with a design. They begin with a conversation about the climate — what the sun does here, which direction the wind comes from, how hot it actually gets, and how a building can work with those conditions rather than against them.
I have been asked more than once whether you really need air conditioning to live comfortably in coastal Oaxaca. The honest answer is no, if the building is designed correctly. I have spent time in houses here that stay in the low 20s Celsius inside on days when it is 35 degrees outside. No mechanical cooling. No thick energy bill. Just a building that understands where it is.
That is what this post is about: the specific design and material choices that make passive cooling work in this climate, and what we encourage — and discourage — at Rancho de las Estrellas.
Start with orientation
The most important decision happens before you draw a single wall. Orientation determines how much heat your building absorbs and how well natural ventilation works.
In coastal Oaxaca, the long axis of a building should run east-west. This minimizes the surface area exposed to the east and west sun angles, which are low in the sky and can drive significant heat gain through walls — especially in the afternoon when west-facing surfaces heat up and slowly release that heat into the interior.
The prevailing breezes here come off the Pacific — roughly from the southwest in most seasons — and your building needs to open toward them, not turn a solid wall in their direction. This is not abstract theory. It is the reason traditional structures in this region are oriented the way they are.
Deep overhangs
A roof overhang of 90 to 120 centimeters does something elegant: it blocks the high summer sun from hitting walls and windows while allowing the lower winter sun through. In a climate where the sun arc shifts significantly between seasons, this passive geometry means your building is shaded when you need shade and lit when you need light.
Deep overhangs also protect walls from the rain load during the wet season, which extends the life of natural materials considerably. Adobe walls, in particular, need to stay dry to perform well over decades.
There is a limit. Very large overhangs — beyond about 60 centimeters on sides exposed to strong wind — create uplift risk during tropical storms. We address this in the building guidelines and cover it in more detail in our post on designing for hurricanes.
Cross-ventilation: this is the real work
If orientation is the first decision, cross-ventilation is where the design actually pays off. A building that is oriented correctly but has no through-passage for air will still trap heat. One that opens to the prevailing southwest breezes and allows them to move from one side of the building to the other — without obstruction — can feel like a different climate entirely.
In practice this means:
- Openings on the windward side at roughly mid-wall height, where the moving air is
- Openings on the leeward side at higher positions, which lets hot air exit above the occupied zone
- Interior room layout that does not block the airflow path with solid walls or solid furniture
- Sleeping areas positioned so that a person lying down is in the path of movement, not in a dead zone
We encourage people thinking through their lot and building layout to do this analysis before finalizing room placement. It costs nothing at the design stage and cannot easily be fixed after the walls are up. You can explore the building approach further on the build page.
Thermal mass and the adobe wall
Adobe is not a fashionable material in the sense that it photographs well on Instagram. It is a practical material that has been used on this coast for centuries because it works.
A well-built adobe wall — typically 30 to 45 centimeters thick — absorbs heat during the hottest part of the day and releases it slowly at night, when the outdoor temperature has dropped and you want warmth, or when ventilation can carry it away. The thermal flywheel effect means the interior temperature is always moderated: not as high as it gets outside during the day, not as low as it gets at night.
Combined with correct orientation and cross-ventilation, adobe walls make the passive cooling strategy close to complete. The building is doing the work that an air conditioner would otherwise do, using nothing but physics and the heat capacity of earth.
Adobe also has low embodied energy compared to fired brick or concrete block. The material is local, the production is relatively simple, and the resulting wall performs better in this climate than either alternative.
Raised floors and foundation ventilation
Ground-level concrete slabs absorb moisture and radiate heat. Even 30 to 60 centimeters of clearance under a raised floor improves ventilation through the building, reduces moisture intrusion, and lowers the effective temperature you experience in a humid tropical climate. This is one of the details that gets negotiated away during construction and regretted later.
Roof design and palm thatch
The roof is where the most heat enters. A low-pitch metal roof in direct sun becomes an oven. A well-designed roof does several things at once: it provides insulation, promotes ventilation, and sheds rain efficiently.
High ceilings give hot air somewhere to go that is not where you are sitting. A ventilated ridge — an opening at the roof peak that allows rising hot air to escape — turns the roof into a chimney effect that continuously draws cooler air up from the living space below.
Palm thatch is worth taking seriously. It has been dismissed by people who associate it with impermanence, but the thermal performance of a well-laid thatch roof is genuinely superior to metal or tile in this climate. Thatch is an excellent insulator. It reflects and dissipates heat rather than absorbing and transmitting it. It is locally available, requires local knowledge to install well, and connects the building to a building tradition that developed here in response to exactly these conditions.
The other materials we use and encourage — local hardwood for structural elements, river stone for foundations and lower walls — carry the same logic. Hardwood is strong, locally sourced, and durable in humid conditions. River stone at the base of a wall keeps adobe above the moisture line.
What we do not use
Concrete block without insulation is the most common building mistake in coastal Mexico. It is cheap and fast to build with, and it performs like an oven in tropical conditions. The walls absorb heat through the day and release it into the interior at night, when you are trying to sleep. It is the reason so many houses on this coast end up needing air conditioning: the building was not designed for the climate, so a machine has to compensate.
Large glazed surfaces facing west invite the same problem. Glass has essentially no insulating value, and a west-facing glass wall in the afternoon sun is a direct conduit for heat gain.
White-painted roofs without insulation are marginally better than dark roofs in terms of reflectivity, but they do not solve the underlying problem. Reflection reduces heat gain; insulation slows heat transmission. You need both.
Solar and water
Every home at Rancho de las Estrellas runs on solar as the primary power source, with grid connection as backup. The solar resource here is excellent. A correctly sized system handles the loads of a passive home without difficulty.
Rainwater collection completes the picture: the wet season provides reliable precipitation, and a properly sized storage tank fed by roof runoff can supply household water through most of the dry season. Gravity-fed distribution from an elevated tank eliminates pump energy entirely.
The result is a home that is largely self-sufficient in energy and water, carries no air conditioning operating cost, and stays cooler inside in summer than most mechanically cooled houses.
The building guidelines at the Rancho are not an aesthetic preference list. They are a set of principles derived from this specific climate, this specific landscape, and the question of what it means to build something here that does not fight where it is. You can read more about the full approach on the build page, or if you are still at the stage of understanding the land and the community before thinking about construction, the vision page is the right place to start.
If you want to come and walk the land — to see how the existing structures sit in relation to the sun and the breeze, and to think about what you might build — the visit page tells you how to arrange that.