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A clear view of installing windows in your new home

Properly installed, windows let air and light into your home, help regulate temperature and — if you're building a new home — give you the chance to make a distinct aesthetic statement.

But windows installation isn't as straightforward as setting a square peg into a similarly square hole. In fact, the process requires a great deal of precision and patience. Here's what you need to know.

Start with the basics

Before any work takes place, decide what kind of windows you want. This includes both window type and pane material, since both affect price and the complexity of installation.

You can choose from the following types of windows:

- Casement windows are a popular, basic type. These windows have two vertical panels (also known as casements), at least one of which swings open on hinges.

- Double-hung windows, meanwhile, are split in two horizontal sashes (again, another word for panels). The bottom sash slides up as needed, while the top sash slides down.

- Awning windows are smaller, less expensive options that have one panel and are hinged at the side or the top, allowing the window to swing open.

- You can also choose custom windows that pull or crank open, include a screen, multiple panels or other options like frosted glass.

In addition, you need to consider what kind of panes you prefer. Acrylic is less expensive than glass, takes more force to shatter and provides superior insulation. It does, however, scratch easily.

The number of panes also affects both price and comfort. Double-pane windows are common and contain a small air pocket left between panes, effectively acting like a layer of insulation. Tri-pane windows are more expensive but lower heat transfer. Some window manufacturers produce multiple-pane windows with gaps filled with gases like argon or krypton, which have a much lower thermal conductivity than air and help limit heat transfer.

Installing new windows

If you're replacing an existing window with an "insert" or "pocket" kit that matches the original specifications, this is a job you can tackle on your own, since all you'll need to do is position and attach the window. In cases where you're building at new home, however, window frames must be created to match window measurements, and the process becomes significantly more complicated.

When you look at a finished window, no gaps are (or should be) apparent. But what's underneath tells a very different story. Though windows fill deliberate holes in your home's structure, they are rarely a perfect fit. Before a contractor places a window, he or she measures it and then creates a rough window opening. This opening closely matches the dimensions of the window but will never be exact. As a result, multiple measurements of the rough opening are taken, and wooden "filler strips" are cut to fit on any side of the opening more than one inch out of alignment with window measurements.

Next, a self-adhering waterproof membrane or builder's felt is attached to the outside frame of the window, starting with the bottom edge. Strips are then placed along both sides and the top, and with care to ensure that no seams are facing up. This prevents water from getting behind the membrane to the wall itself.

Nailing the window in place using supplied nailing fins comes next. As each corner is attached, installers should stop to make sure the frame is level. Once nailed into place, more waterproof membrane is used along all outside edges, and metal flashing is installed.

Often, flashing will be supplied and should be used as directed. As stated by the International Residential Code (IRC), "Windows and doors shall be installed and flashed in accordance with the fenestration manufacturer's written installation instruction." That doesn't mean a window contractor gets a free pass if no flashing is supplied, however. In this case, he needs to create flashing that extends three inches up the wall and one-quarter inch beyond each casing edge.

Finally, expanding polyurethane foam should be used inside the home to seal the gap between window and frame. It must be applied slowly, and given time to expand. If too much is applied too quickly, the window may bend.

Your window contractor

Should always look for ways to make windows water and air-tight, not cut corners. Reputable windows installers do more than required by code or by law, and strive to protect your home in over the long term.

To make sure you're not hiring a scam artist, check trusted online review sites like Angie's List, talk to friends and neighbours — then go look at their windows. Never take glowing assurances of a window professional at face value: His work is his word.

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