Badgir (Windcatcher)

A badgir, from Persian bâd (wind) and gir (catcher), is a tower that rises above a roof to bring moving air into a building and let warm air out. Windcatchers are a defining roof feature of hot, dry parts of Iran, and related towers are found around the Persian Gulf, where the Arabic name barjeel is used, and in Egypt, where the traditional form is the malqaf.

How it works

A windcatcher works in two ways:

• Wind pressure. Openings facing the prevailing wind push air down the shaft into the rooms below, while suction on the sheltered side draws stale air out.
• Stack effect. On still days, warm indoor air rises and escapes through the tower, pulling cooler air in from courtyards or basements.

Air can be cooled further as it passes over water, wet surfaces or cool masonry and soil. Towers can also flush a building with cool night air. Reported indoor temperature reductions compared with outside air are in the range of 8-12 °C (14-22 °F), though actual performance depends on design and weather.

Design variations

Windcatchers may have one, four or eight openings. Square shafts are generally more efficient than round ones, and taller towers reach stronger, cooler air. In Yazd the towers are typically four- or eight-sided, while in nearby Meybod they are short and single-sided. The tallest Iranian examples reach about 34 m (112 ft); one of the tallest surviving stands in the Dowlatabad Garden in Yazd. Traditional materials are adobe, fired brick, stone and plaster.

Roofs and the city

In the Historic City of Yazd, a UNESCO World Heritage site, buildings are made of earth, roofs are formed as vaults and domes, and windcatchers punctuate the skyline alongside minarets. UNESCO describes how windcatchers, courtyards and thick earth walls together create a comfortable microclimate. Water reaches the city through qanat tunnels, and many traditional water reservoirs (ab anbar) are also ventilated by windcatchers.

Modern revival

Windcatchers declined in the 20th century as mechanical air conditioning spread, but they have attracted renewed interest in the 21st century as a low-energy cooling method. Contemporary versions use lightweight metal or fabric and sometimes combine with mechanical ventilation.