THE FINE ART OF HUMIDITY CONTROL.

The Carnegie Museum of Art in Pittsburgh uses its Gallery 12 to display traveling exhibitions, which require strict relative humidity conditions year-round. During recent winters, on cold days, condensation has dripped from Gallery 12's skylights, and icicles have formed outside the building.

The museum's administration commissioned Pittsburgh neighbor Butt Hill Kosar Rittelmann Associates to design a system that protects the gallery and its art by keeping humidity stable throughout the year. It was also important that the new system not disturb the layout of Gallery 12, which was designed by the eminent architect Edward Larabee Barnes in the early 1970s.

In the winter and spring of 1998, Burt Hill's architects prepared a preliminary study by surveying the insulation and air/vapor barrier of the walls and skylight, analyzing the airflow path through the gallery the wall plenum, and skylight attic, and studying air pressures in the gallery. After receiving a green light from the museum's administrators, Burt Hill composed the actual design from summer 1998 to early 1999, and construction began in February 1999. Work was completed last July.

In order to rehabilitate Gallery 12, Burt Hill reinsulated the gallery walls with a continuous air/vapor barrier composed of three inches of polyurethane cellulose called URE-K made by International Cellulose Corp. of Houston. The company added one inch of cellulose fireproofing made by W.R. Grace & Co. and reglazed the skylights with insulating and shading glass made by Fisher Skylights of New York. The skylights got a retractable shading system fabricated by Solar Veil of New York, a company that has provided similar shading systems in many other museums.

Burt Hill designed a ducted air return system in the interstitial space behind the gallery walls, as well as an air heating system in the gallery attic that is activated on very cold days when there is a risk of condensation. Finally, Gallery 12 was equipped with its own dedicated air-handling unit to combine heating, cooling, humidification, and dehumidification functions.

The new gallery was used for the first time this winter as the site of the Carnegie International, an important survey of contemporary art from around the world.