ANA'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.
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.
Sana’a townhouses also have a number of other “built-in” cooling and heating systems, Ayssa said. For example, most of the living rooms feature half moon-shaped stained-glass windows above the windows, to allow light to enter when the thick wooden shutters are closed against the afternoon sun. Most also have small, high vents, called shaqous, above the normal windows, which provide cross-ventilation without compromising the privacy of those inside.
“Some of the designs take culture into account, too,” Jerome said. “In a lot of these places, women are not to be seen.”
Most of the tower houses also feature small, clay-latticed windows, which protrude about a foot from the external wall. Because of the way the wind moves through the shaded vestibules, people use these windows as either natural refrigerators or, by placing a bowl of water on the shelf, as electricity-free swamp coolers, said Adel Abdullah Homaid, who works for a Sana’a-based architectural preservation organization. “People still use it, yes. It actually works,” he said.
The most important aspect of the tower houses’ green-friendly design is simply the orientation and strategic placement of east- and west-facing windows, which were specifically designed for Sana’a climate and latitude, to account for where the sun will rise and set in the different seasons, Ayssa said.
“A lot of the design is thousands of years old. It’s simple, but it is the result of centuries of experimentation,” Ayssa said. “In comparison, the way we build today is so stupid.”
In Yemen, people didn’t start building the “modern way” — using mostly concrete — until the early '80s. “It’s terrible material for a desert environment. It’s cold in the winter and hot in the summer, it’s way too costly, and there’s simply not enough electricity in the valleys to heat and cool the houses,” Jerome said. “Today, you see people returning to the traditional mud house, just for comfort.”
Jerome, who is also a partner at the New York City architecture and engineering firm, WASA/Studio A, said people in the West are starting to catch on, too.
“When you look at these buildings in New York that have flimsy walls and are totally sealable so you can pump in heating and cooling, you think, what were we thinking? They’re white elephants,” she said. “Buildings should take into account the climate — if it’s cold in the winter, or hot in the summer — and we should build them with those factors in mind.”
Without increased preservation efforts, some of the tower houses of Old Sana’a may collapse in the next decade, said Ayssa.
“It is a UNESCO Heritage Site, but it’s not a museum. People live here now and have lived here for thousands of years,” he said. “Right now, we must preserve what we can, and learn what we can from the old techniques.”
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