Secondary Author(s)

Withers Jr., Charles

Report Number






Suspended t-bar ceilings are common in commercial buildings. Research has found that these ceilings are very leaky, and several problems arise from this. If the space above the ceiling is vented to outdoors, the entire building becomes leaky. Furthermore, if the insulation is located at the ceiling rather than the roof, then the ceiling space will be hot (summer), and if the ceiling space is also vented to outdoors, then the ceiling space will be hot and humid. The thermal and humidity conditions of the ceiling space have important implications for space conditioning loads, building ventilation rates, and indoor relative humidity. Conductive gains through ductwork add to loads, and various forms of uncontrolled air flow readily move air between the ceiling space and the occupied space. These factors should be considered during design and construction of commercial buildings. Best practice: locate the air and thermal boundaries of the building at the roof deck. This approach has many benefits.

Date Published



Reference Publication: Cummings, James. B. and Charles R. Withers, "Best Practice for the Location of Air and Thermal Boundaries in Small Commercial Buildings", Proceedings of 12th Annual Symposium on Improving Building Systems in Hot and Humid Climates, San Antonio, TX, May 2000.

Local Subjects



FSEC Energy Research Center® Collection



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