Slightly bowed low-E windows can focus sunlight and ignite fires
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- Low-E window glass is coated with a thin metal or metal oxide layer that reflects infrared while letting visible light through, keeping buildings warm in winter and cool in summer.
- If low-E glass is slightly bowed, the curved surface acts like a magnifying glass, focusing reflected heat on a concentrated spot or along a line.
- Concentrated reflected sunlight from low-E windows has scorched wooden decking, melted artificial turf, and damaged plants, according to the source.
- In one case, three fires in a single week were traced to a neighbour's newly fitted low-E windows; the affected homeowner moved a propane tank that sat close to the focal point.
- Architects now avoid curved reflecting glass that produces "skyscraper death rays" in larger buildings, but the smaller domestic version is less obvious to spot.
- Any low-E window could potentially ignite nearby materials if it is poorly manufactured, the source notes — a risk distinct from the high-profile tall-building cases already mitigated by design standards.
Why it matters: Homeowners adopt low-E glass for its energy-efficiency benefits, but the source frames this as 'a rare side-effect' tied to bowed panes and poor manufacturing rather than the technology itself. Unlike architects of tall buildings who now design around curved reflections, domestic installers and homeowners may not recognise that a slightly warped window can focus enough sunlight to ignite a neighbour's property.
