When Viktoria S. Singer lifted a loose roof tile in Fes on 19 August, a cold draft brushed her hand in air that measured 41°C (106°F) outside. The tile setter had expected to find cracked plaster. Instead, a narrow opening led into a sealed shaft and a branching maze of clay-lined passages beneath the house.
Researchers who examined the structure say it is a remarkably intact passive cooling system, probably built in the late 16th century. Sensors placed in the house recorded air temperatures as low as 24°C (75°F) indoors while the courtyard reached 39°C (102°F), with no powered fan or compressor running.
A draft behind the plaster
Singer said she first thought the breeze came from a broken drain. “I put my face near the opening and it felt like standing next to a cellar,” she said. She called the house’s owner, who asked a local climate laboratory to inspect the cavity before builders closed the wall.
The team found a 62-metre (203-foot) route of narrow channels leading from a shaded roof intake to a chamber beside an old cistern. According to climate researcher Agnesa Marek, the design uses moving air, damp clay and the building’s cool lower levels to draw heat from rooms. Water in the chamber helps cool the air as it passes; the system needs no electrical supply.
We found a machine made of earth, air and patience — and it is still doing its job.
Agnesa Marek, climate researcher
Cooling without a motor
Over 18 days of monitoring, Marek’s team measured an average temperature difference of 9.4°C (17°F) between the courtyard and the rooms served by the channels during the hottest afternoon hours. The greatest gap was 15°C (27°F). The researchers have not yet published their results in a peer-reviewed journal, and say the readings come from one house, not a controlled trial.
A second building nearby has a similar vent and chamber, though its passages are partly blocked. Singer’s discovery prompted residents to let researchers inspect four more old houses; two showed traces of comparable air channels. The team is now using small sensors and ground-penetrating radar to map what may be a wider tradition of passive cooling in the medina.
The finding comes as Fes and other Moroccan cities endure longer periods of dangerous summer heat. Modern air-conditioning is spreading, but it can strain electricity supplies and send hot exhaust into narrow streets. Marek said the old design is not a ready-made substitute: it depends on dry air, careful upkeep and buildings constructed to channel shade and airflow.
The researchers plan to test whether the channels can be cleared without damaging their fragile clay lining, then compare readings through next summer. The city’s heritage office has asked the house owner to leave the shaft accessible while the study continues. Singer, who has returned to tile work, said she now pauses whenever a wall gives off an unexpected breeze.
