Low-e windows keep homes cool but may set neighbours' property on fire

Special windows called low-emissivity, or low-E, windows are good for the environment. They help keep buildings warm in the winter and cool in the summer. However, there is a rare problem that can happen with these windows, which can even start fires in neighbouring properties.

These windows have a very thin coating of metal or a metal oxide. This coating allows normal light to pass through, but it reflects infrared heat. In winter, this means heat inside your home stays inside, keeping it warm. In summer, it bounces away the sun's heat, helping to keep your home cool.

The issue is that the reflected heat needs to go somewhere. If the glass has a slight curve, it can act like a magnifying glass. This curved glass can focus the heat onto one specific spot or along a line. There have been cases where this concentrated sunlight has damaged things like wooden decks, melted fake grass, and harmed plants.

In one serious incident, a series of fires was discovered to be caused by the low-E windows recently installed in a neighbour's house. After three fires happened in just one week, the person whose property was affected moved a gas tank that was near the area where the heat was being focused.

Architects are now aware of these risks, especially with large buildings. They know to avoid using curved reflective glass that could create a dangerous effect, sometimes called 'skyscraper death rays'. However, the problem might be less obvious with smaller windows in homes. Any low-E window could potentially cause a fire if it's not made perfectly.