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Green technology — it's older than you think

In Yemen, 800-year-old houses provide all the comfort of a modern, cutting-edge structure.

SANA'A, Yemen — The Old City of Sana’a looks a little like a gingerbread house, delicately frosted on Christmas Eve, and then rediscovered months later in a cabinet above the radiator.

This ancient, walled city is a dilapidated rabbit warren of medieval towers intricately adorned with alabaster crescents. Centuries of rain, sun, coups and civil war have taken their toll on its 800-year-old buildings. But despite their age and dilapidation — it's shocking that any of these structures are still standing at all — the buildings feature some impressive green technology.

“It seems to me the architects in the past were much more clever than us,” said Abdullah Zeid Ayssa, who overseas the government’s preservation efforts in the Old City of Sana’a, the whole of which is a UNESCO World Heritage Site. “Our modern architecture doesn’t care much about the sustainability of the materials, or the climate [a building] will exist in.”

Roughly 6,000 “tower houses” — narrow, four to five-story structures built side-by-side, like Brooklyn brownstones — still stand in Old Sana’a today. Nearly all of them were built by hand using locally quarried stones, hand-mixed plaster and a naturally waterproof insulating material, qudad, made of volcanic cinders and lime.

Sana'a Old City in Yemen at night
The Old City of Sana'a is listed as a UNESCO World Heritage site.
(Paul Stephens/GlobalPost)

Both the materials and the centuries-old building techniques help maintain a constant temperature inside the homes, eliminating the need for air-conditioning and central heating — a key factor in the poorest nation in the Arab world, where millions of people live without electricity, and power outages in the major cities occur on a daily basis.

“If your house is made of cement, it’s cold inside, but if you live in an old house, it’s much warmer,” said Taha Ahmed, who has lived in a 100-year-old tower house his whole life, and have never used either a heater or air-conditioning. “It is insulated by clay walls, so it’s quiet and warm all winter.”

Ayssa, who studied architecture at Texas A&M University, said the comfortable interior temperature is largely due to the buildings’ “passive solar” technologies, and naturally efficient “thermal mass.”

“Basically, that means [the tower houses] soak up the heat of the sun during the day, and release it gradually at night, so it creates a perfect environment year around,” said Pamela Jerome, a professor of historic preservation at Columbia University’s Graduate School of Architecture who has worked extensively Yemen. “It’s not a fancy technology, but it works.”

Despite the soaring and plummeting temperatures of a desert city situated at more than 7,000 feet, the internal temperature of Sana'a tower houses rarely fluctuates more than a few degrees, according to Ayssa’s doctoral research.