Low-emissivity windows also keep houses warm in winter, but use on bowed glass can have magnifying-glass effect

Low-emissivity or low-E window glass is a useful green technology for keeping buildings warm in winter and cool in summer … but a rare side-effect can set the neighbours’ property on fire.

The glass is coated with a thin layer of metal or metal oxide which lets visible light through but acts like a mirror in the infrared. Heat from the interior is reflected back in, retaining warmth in winter, while unwanted solar radiation is repelled in summer.