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Tue, Sept. 24

Low-e windows great for homeowners, but not for neighbors with vinyl siding

I've been saying it for years. I've written about it in this column and other publications. I've even taught classes on it - communication.

You can be the best inspector in the world. You can have 20,000 inspections under your belt. You can have dozens of certifications. But if you can't communicate what you found to the client, you might as well stay home and watch "Law and Order."

Last week, I was going over my notes with a client. I was talking about the attic, and I told her there was 12 inches of loose fiberglass insulation in the attic, about R-30. Then I told her there was batt insulation on the skylight walls in the attic. I started talking about the attic ventilation when I noted a concerned look on her face. I asked her if she had any questions. She said, "I don't want any bad insulation. Should I ask the sellers to replace that with good insulation?"

It took me a second to understand, and then I explained that there was "batt" insulation in the attic. This is insulation on a roll rather than loose insulation, and there was nothing wrong with it. I'll be more careful when describing insulation in the future.

I've learned some new things about low-e glass. This stands for low emissivity, and is basically a thin metallic (but transparent) film on the glass. The film will reflect ultraviolet and infrared (heat). In Arizona, the film is facing outside, so it will reflect the sun's harmful ultraviolet rays, and will reflect heat from the sun. These windows can reduce your cooling bills and make your home more comfortable. In northern areas with very cold winters, the low-e coating is reversed, so it reflects heat back into the home and reduces heating costs.

Some builders in northern climates actually use different windows on different walls. They have the low-e reflecting out on the south facing windows to avoid heat gain in the home in the summer. And on the north-facing walls they have the low-e facing in to avoid heat loss from the home to the exterior.

I sometimes find some of the low-e windows reversed. This is not a major concern. A reversed low-e window does not magnify the ultraviolet light or heat; it simply does not reduce them. As with northern climates, it will help reduce your winter heating costs. But this is not as efficient in our climate as having the low-e facing the exterior. Unfortunately, reversing the windows is usually expensive and not cost-effective.

I've also said in this column that no matter how experienced a home inspector is, and no matter how many classes a home inspector takes, you will always encounter something you've not seen before. I recently inspected a newer home with low-e windows. I found several reversed, which surprised me because the home was very high-quality. I showed my fancy low-e tester to the buyers and explained that improvement may not be cost-effective.

After the buyers left, I tested the windows from the exterior and found there was low-e facing out. There was also low-e facing in. I pulled out my trusty Droid and started looking at window manufacturer websites. I found there are "double-low-e" windows. These have the film on both sides, so you get both summer and winter benefits.

I had not encountered these windows before (possibly because they are very expensive). I put a long note in the inspection report explaining that there was nothing wrong with the windows, and in fact they were upgraded windows. So now I know I have to check low-e windows both from the interior and exterior.

Low-e windows are a good investment: They can pay for the extra cost of the windows in just a few years. And if you don't think they work, there is mounting evidence that low-e windows (facing out) have damaged the vinyl siding on nearby homes. Reflected heat from windows damaging vinyl siding has been known for years, even before low-e windows. Double-pane windows seem to cause more damage. The thought was that the outer pane on double-pane windows can bow inward due to differences in pressure. This makes the window slightly concave, and concentrates the reflected heat.

There are technical bulletins from glass manufacturers and testing laboratories confirming incidences of damaged vinyl siding from heat reflected from windows. Vinyl siding manufacturers don't like to discuss this, but it's noteworthy that some manufacturers warranties exclude damage from reflected heat from windows. It's also noteworthy that some vinyl manufacturers offer products made with CPVC instead of PVC. Polyvinyl chloride (PVC) is the plastic used in vinyl siding. It is also the plastic used in PVC water supply lines. And chlorinated PVC (CPVC) is the "yellow" PVC piping used for hot water supply lines, because CPVC is more resistant to heat. Unfortunately, CPVC vinyl siding costs much more to manufacture, so it is much more expensive.

With the increased use of low-e windows, there have been more reports of vinyl siding damaged by window reflections. The National Association of Home Builders (NAHB) reported recently that the incidents of damaged siding from window reflections have increased in the same proportion as the increased use of low-e windows. So while you're keeping your home comfortable and reducing your cooling costs, you might be melting your neighbors' vinyl siding.

Randy West owns Professional Building Consultants in Prescott. He is a state-certified home inspector and has performed almost 6,000 home inspections in the Prescott area. West is past president of the Arizona chapter of the American Society of Home Inspectors, and currently serves on the Home Inspector Rules and Standards Committee for the Arizona Board of Technical Registration. Contact him at

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