Is radiation control recommended for all low-slope roofs?
With current methods to achieve radiation control on low-slope roofs, radiation control is a passive technology. It works night and day, all year round, except during rainy periods or when the roof is covered by dew. A layer of water has high infrared emittance. This dominates the nighttime behavior of a dew-covered roof. Even if air temperatures are several degrees above freezing, thin layers of water exposed to the night sky will freeze on clear nights. Until solar energy evaporates ponds or dew from a roof, the roof temperature remains near the ambient air temperature. In effect, therefore, even though it complicates the energy effects, water on a roof enhances radiation control. Since solar radiation control cuts down on the amount of solar radiation absorbed by a roof, there is less heat gain during sunny periods through a roof with radiation control than without it. This heat gain may be desirable during the heating season. The diminution of heat gain during the heating season by
