Night Sky Radiation

Roof cladding absorbs radiation from the sun and the attic space becomes warmer; some of this heat is radiated into a clear sky at night.

Because all objects radiate heat to cooler objects, night sky radiation will occur when there are no clouds in the sky. The radiation rate depends on the emittance of the roof cladding.

Radiation to the sky can cause the cladding temperature to drop as much as 5˚C below that of the surrounding air; that causes dew when the surface temperature reaches dew point or frost if the temperature falls below zero.