Field Applied Polyurethane Foam in Building Envelopes: The Systems Approach to Buildings

Abstract

energy was inexpensive. Our approach to environmental control of buildings has changed since that time. Increased tightness of building envelopes, controlled ventilation and air conditioning systems are relatively recent changes in the bmlding technology. Recent trends to thicker thermal insulation in cold climates caused the primary exhaust device, the chimney flue, to be used less frequently. 52 The trend towards using electric heating, heat pumps, and power-vented sealed combustion furnaces has further eroded the role of a traditional active chimney. Chimney flues acted as exhaust fans, which extracted great quantities of air from the conditioned space, reducing the moisture load acting on the building envelope. Less efficient chimney flues increased the indoor air humidity, increasing frequency of vapor condensation on surfaces of windows or thermal bridges. More recently, the significance of this issue was reinforced by in-