A New Rooftop Coating Makes Buildings 'Sweat' To Cut Cooling Costs

By absorbing moisture when it rains and expelling it as vapor when it becomes warm, buildings can essentially sweat just like humans.

Sweating Rooftops
In tests on model homes using an infrared camera, the house on the right (covered in the "sweating" polymer) remains cool while the house on the left (covered in a regular polymer) absorbs heat and grows warmer.Rotzetter ACC et al. / Advanced Materials

Researchers at ETH-Zurich are borrowing from biology to cool buildings in a novel way: by making them "sweat." They've developed a permeable polymer mat that can be spread across rooftops to absorb moisture like a sponge when it rains, locking it inside. But when heated to a certain temperature by the sun the material becomes hydrophobic and pushes the water out. Just as humans expel heat from the body by imparting it to sweat on our skins that then vaporizes to carry the heat away, so would these "sweating" buildings remain passively cool by imparting their heat to water evaporating into the atmosphere, shaving up to 60 percent off air conditioning loads.