Why metal-roof sheds get so hot, and how a radiant barrier fixes it

Anyone who has worked under a metal roof in April or May knows the feeling: by noon the heat seems to pour down from the ceiling. It is not your imagination. A sunlit roof sheet gets very hot, and a hot surface sends its heat downward as invisible infrared radiation, straight onto people, machines and stored goods.

Three ways heat moves

• Conduction: heat passing through a solid, like a hot pan handle.
• Convection: heat carried by moving air.
• Radiation: heat travelling as infrared rays across an air gap, like warmth from a fire.

Under a hot roof sheet, radiation is the big one. Fans move air around, but they do nothing to stop the roof from radiating heat down onto everything below it.

What a radiant barrier does

A radiant barrier is a sheet with a highly reflective aluminium surface, fixed under the roof sheeting. Instead of the radiated heat reaching the space below, the foil reflects it. Our COOL ROOF FWF grade has a reflectivity of 97% and an emissivity of 0.03, tested to ASTM E408. In plain words: the foil bounces back almost all of the radiant heat that reaches it, and gives off very little heat itself.

Where it makes sense

• Factories, warehouses and pre-engineered buildings with metal roofs
• Poultry and farm sheds
• Workshops, godowns and site offices
• Walls of PEB structures facing the afternoon sun

A radiant barrier is not a replacement for ventilation. It works best together with good air movement, because it stops the heat at the roof before it gets in.

Made in Badlapur

COOL ROOF radiant barrier is made at our own plant at Badlapur MIDC near Mumbai, in 1200 mm wide rolls, with regular grades dispatched in about 7 days. Platinum Polymers has been in the trade since 1992.