Greendo: Undulating Geothermal Homes Built Into the Side of a Mountain

greendo by keita nagata

all photos by Shinkenchiku-sha

As if being a small island nation wasn’t enough, 73% of Japan’s land is occupied by uninhabitable mountainous regions. So flat land obviously comes at a premium. But one architect has now gone where others have tend to shy away: into the sloping side of a mountain. Completed earlier this year, Greendo is an undulating 7-unit residential building that’s been carefully inserted into the side of mountain in a town in Takamatsu City, Japan.

greendo by keita nagata

rendering of the 7-unit Greendo apartments

The sloping site of Greendo (green + do, which is Japanese for earth) had been left untouched for years until local architect Keita Nagata came around. Instead of flattening the land and building upward, Nagata proposed a radical new design in which each unit, instead of being stacked on each other, were delicately pushed into the side of the slope. Not only did the idea relieve stress that would have been place on the land and structure, it yielded an organic structure that seamlessly integrates itself into the landscape.

greendo by keita nagata

the ventilation air tubes that geothermally heat and cool the apartments

But if this was going to be a home built into the side of a mountain, Nagata wanted to take it a step further. He wanted to create a fully passive home that lived and breathed with the land. Ventilation tubes that connect to the homes travel underground and in the summer the earth naturally cools the air. Conversely, in the winter the air is warmed. Solar panels are also mounted on the roofs, which function as the neighbor’s yard as well. Humidity was a big concern so several layers of anti-humidity insulation were incorporated into the walls.

The units range from 66,000 yen (about $530) to 135,000 (about $1000) per month but it appears that all units are already rented or in contract.

greendo by keita nagata

greendo by keita nagata

greendo by keita nagata


  1. I’ll be curious how these hold up to a few Japanese summers. Our first house here had a garage that was underground and water seeped through the walls, especially when it rained. The garage was a hideous no-go zone. We had to take a week long trip our first summer here, and a typhoon was on the way, so I battened down the house and shut up the garage. When we came back, everything in the garage had a layer of mold on it. We had to through almost everything away.

  2. this looks amazing! i hope it catches on – would love one of my own ^^

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