Underground houses for hot days

The traditional buildings where we are in the Andes1 are built to stay cool on hot days. They have thick rammed earth walls, tall ceilings, large doors and windows to provide draft, wide corridors for shade, and are often in the shade of big trees.

We have built that way too, although it still gets hot on hot afternoons, especially in the dry season.

I am thinking of building an underground building with a living roof near the main houses. It will function as a living room on hot afternoons, and perhaps even a bedroom on warmer nights.

Building it into the ground will keep the temperatures down, as will the living roof.

As for details, I am thinking of a round room, 4-5 meters interior diameter, with stone walls, and with the wall facing out also in stone with a large door. It will likely have ventilation shafts to create a nice draft.

The walls will need a water barrier, and the roof may need extra insulation in addition to the soil and plants.

The main space is down a few steps from the entrance level. This allows the building to be built further down into the ground, and it will create a space to collect the cool heavier air that sinks.

I will have to explore what plants are suitable for the living roof. They need to have relatively shallow roots and be drought-resistant. A variety of succulents may work well.

We will also plant trees for shade, and create a multi-layered food forest around the house to further reduce the temperature.

It will not have a kitchen or bathroom since those will be in the main buildings. This is more of a retreat and/or cooling space.

Daytime temperatures are typically between 20 and 30 degrees Celsius, with rare days above 30 degrees. Night temperatures are typically in the mid teens to low twenties. I slept outside during the hottest time of the year, and it was comfortable. I suspect the temperatures in this room may be between the high teens and low twenties.

Why don’t they traditionally build into the ground in this area? I assume it’s partly because they don’t need deep foundations (no frost) so they don’t have basements2. And it has also not been necessary. These days – with climate change, increasing temperatures, and more extreme weather – it makes sense to include at least one underground room. For all I know, this may be the first in the area built in this way. (Some friends of ours have outdoor toilets built similarly, but it’s not a living space.)

The drawings above are two quick diagrams I made of the plan and elevation.

(1) Barichara at 1000 meters above sea level and 6 degrees north of the equator.

(2) When the ground freezes, the foundation needs to go deeper than the frost. In cold climates, that means it makes sense to have basements since they already dig quite far down so you may as well make use of the big hole in the ground. In climates without frost, the foundation doesn’t need to go very deep into the ground, so the hole is more shallow, and it makes less sense to make a basement out of it.

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