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What to Look for in Window Construction

Monday, November 30th, 2015 by Ben Kershner


Slider construction detail - SunriseRecently, I talked about the specification numbers listed on the window label, and how they affect the thermal performance of your new window.  You should never buy a window without knowing the U-Factor and SHGC of the product you’re buying.  That said, there’s lots more to know about your window than the numbers on the label.  Look at the glass package, the framing, and the hardware.  You probably will also care about visual appearance of the window, and the custom options that are available.

Single Pane WindowFirst, know how it’s designed to be installed.  Is this a new window with a full tear-out of the old one?  Is this a standard framed replacement?  Is it a compression-fit replacement?  Make sure you know the differences.  Compression jambs are cheap, but they’ll never be terribly air-tight.

New double pane window - SunriseThe glazing package in a new window may be double or triple pane glass.  The space between the layers may contain air, argon, krypton, xenon, or some other inert gas.  A wider gap between the panes usually means a better insulating glass-pack.  The edge of the glass-pack should be well sealed to keep the inert gasses inside — if the seal is broken, then the window doesn’t insulate well, and humidity may become trapped between the glazings.  High-quality windows will have a seamless stainless steel spacer with a silicone “thermal break.”  Watch out for aluminum spacers with a seam at every corner.  They won’t last as long.  Low-E coatings and tinting on the glass are located on the inner sides of the package, so they won’t get scratched.  Also notice the amount of glass compared to the amount of frame — different brands may give you less view in the same sized window.

Window condensation forms when warm air hits a cold window.The framing of the window and the sash are usually made of vinyl, or “uPVC” — the “V” in “PVC” stands for vinyl.  It’s the same material that vinyl siding is made from.  The vinyl in your window provides structure and stability.  A thicker vinyl means a stronger, longer lasting window.  Inside the vinyl, you want the best insulator possible.  Hollow frames won’t insulate terribly well (and wood is a terrible insulator), so look for a foam-filled window.  Windows frames can be built with with a pre-cast styrene-foam rod inserted into the hollow portions, or completely filled by injecting a polyurethane expanding foam.  By using expanding foam, manufacturers can prevent air-circulation within the window frame that could otherwise cause “convective loops” — a conveyer-belt of air moving the heat out of your house all winter long.

The hardware in your window includes the locking mechanism and whatever it is that keeps the window from falling back down when you open it.  Windows used to stay open because of big heavy counterweights in the walls.  Today, windows use springs.  There are three common spring types, and each will let you open the window a certain number of times before the spring needs to be replaced.  The best is a block-and-tackle style mechanism.  It lasts significantly longer than other styles, and is easier to replace.  During operation, it provides smooth even resistance along the entire distance.  The locking mechanism on your window may be raised or recessed.  There should be plenty of extra reinforcement and rigidity around the lock for security.

If you like the glazing, the framing, and the hardware, and you’re comfortable with the performance specs, take a look at the visual appearance and options that are available.  Check out colors and wood-grain appearance options.  Little details such as flat or sharp angles and smooth curves and bevels can create a subtle but noticeable change in the appearance of your home.  You may want simulated dividers, or decorative cut glass, or built-in mini-blinds!  There are LOTS of options to choose from.

Is there anything else to look at in a window?  YES!  Don’t forget the warranty.  Does it cover labor, or just parts.  How long does the warranty last, and is it pro-rated?  Does it cover only manufacturing defects, or does it include accidental damage?

About the author

Ben Kershner

Ben Kershner is a home energy advisor at True Energy Solutions, and is a regular contributor to our website. He lives with his wife and family in Greece, NY.

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