With a fair amount of buzz recently about how some energy-efficient windows can create a laser-beam effect that warps siding on a neighboring house, we thought we’d check into the hubbub.
Bottom-line: It doesn’t mean you should abandon your decision to invest in low-e (low-emissive) windows, which limit heat transfer so that your house stays cool or warm. In fact, some areas require low-e windows on new homes or in retrofits.
Anyway, the melting tends to occur under a perfect storm of conditions — so not very often.
Still, we’ve got some tips for you, below, in case your window or your neighbor’s window has turned into a ray gun.
Probably a more important issue is whether you need to replace your windows at all. Our guide can help you make that decision.
What Causes the Laser Beam?
Here’s one theory from the National Association of Home Builders (NAHB): Changes in barometric pressure can sometimes cause low-e windows to bow inwards and magnify reflected sunlight. It’s like training a magnifying glass on an ant; the heat beam toasts anything in its path to more than 200 degrees Fahrenheit. Vinyl siding starts to warp at around 165 degrees.
But a white paper published by the Lawrence Berkeley National Laboratory says there’s been no extensive study on the topic, so whatever is causing the melting isn’t fully understood. Here’s what is known:
- Warping could happen any time of year.
- South-facing low-e windows appear to be responsible for a large number of incidents.
- Damage to neighboring homes happens where houses are close together — up to 20 feet, according to the International Association of Certified Home Inspectors.
What are Industry Insiders Saying?
The Vinyl Siding Institute acknowledges the problem, but claims that heat distortion from low-e windows is rare. However, the NAHB says that as low-e windows have become more prevalent, melted vinyl siding has become more common. So much so that major vinyl siding manufacturers have updated their warranties to exclude heat damage caused by windows.
How Do I Stop the Laser Beam Effect?
To keep a window from cooking stuff in its path, including your deck furniture or car:
- Install windows screens over the outer window. This will diffuse the reflected sunlight.
Related: Well-placed trees and shrubs are natural energy-efficiency boosters.
To protect vinyl siding:
- Replace damaged siding with heat-resistant vinyl siding.
Note: Heat-resistant siding can only withstand temps of up to 220 degrees. Plus, it costs up to three times the price of the regular siding.
Related: Siding: A Guide to the Options