May, 2007

The Case of the Melting Siding

By Steve Easley

A: I have seen this happen before and no, it does not mean that the siding is defective. This problem is typically caused by sunlight that is reflecting off a window on the house next door. All solar energy that hits a surface is absorbed, reflected, or transmitted. Many energy codes today require low-e windows, which substantially reduce energy costs and increase comfort. In fact, in many climates, up to 45% of a home’s cooling load is from solar gains through the windows.Low-e windows achieve their low solar heat gain status through transparent coatings on the glass that can reflect up to 65% of the sun’s heat. Typically, the amount of solar energy that strikes a surface is in the range of 250 btu’s per sq. ft. A combination of product and climate factors can create a “perfect storm” of conditions that can cause vinyl siding to significantly deform. It happens like this: The heat from the sun strikes the low-e window. This heat is then reflected and focused like a magnifying glass onto the vinyl siding of the house next door. I’ve taken thermal readings in these situations where siding surface temperatures have reached 171ºF. Vinyl siding has a low melting point, and as it absorbs this intense heat, it deforms. The vinyl siding products that are most affected by this are light-gauge products that are darker in color. Even light-colored siding in a thin gauge such as .040 can be affected in some circumstances.This problem is worse today because of narrow lot lines and houses that are close together. It’s also worse when the orientation of the house means that heat from the sun reflects onto siding for a few hours a day.

Solution:

Encourage your builder and homeowner customers to consider the distance between homes, a home’s orientation to the sun, and window locations when selecting a siding material.

It may also be a good idea to educate your customers about heavier-gauge vinyl siding. Gauges go up to .055.

If your customers are encountering this problem after the structure has already been built, consider a fabric sunscreen (similar to a bug screen) that completely covers the window. (You can find one example of this type of product at www.phifer.com.)