Replacing home's windows takes some instruction

With 35 million windows set to be replaced in homes this year, those who think the tradeout is as simple as a few minutes to plunk the same size window into an existing hole sealed with a bead of caulk, had best think again.

The switcheroo is far more complicated, and if not done right, you set your home up for water and air leaks and generally poor window performance.

At least one window expert cites a high incidence of wrongly installed windows as the result of homeowners and installers who take the job too lightly, don't follow instructions, or try the equivalent of forcing a round peg into a square hole.

"People don't realize how complex a building is," says Wally Corwin, manager of product integrity for window maker Jeld-Wen. "From the outset it sounds easy, but how to install a window to adapt to the original building structure is one heck of a challenge."

The process begins with accurate measurements, and that's where many homeowners fall short, says Corwin. It's a mistake to measure from molding to molding, when the homeowner should instead remove the molding -- carefully -- and measure dimensions from inside the home.

Weatherproofing windows

Removing the molding also exposes the primary culprit in the failure of a window to perform its No. 1 job: stop water leaks.

Most homes have some sort of weather membrane -- or "water plane" according to Corwin --that underlies the exterior and abuts the window. At some point the homeowner must combine this existing layer to the anti-water portions of the window. Most window makers provide detailed instructions to mesh these materials. Fix any rips or holes in the membrane before installing the windows.

Usually, this connection is made between the window flashing and the membrane. But that's merely a good start, according to Corwin.

Don't automatically buy a window with an overly snug fit. Corwin says., "You'll be stuffing membranes and drain pans in there" along with added flashing, insulation against cold air and other sealants. Too tight a fit can result in a window that binds or drags when operated.

Part of correction operation is a window that is plumb. Window openings are frequently off-kilter or not square. Use shims to correct any imbalance.

Now for the caulk. According to the Window & Door Manufacturers Association, two in three replacement windows are vinyl. But vinyl or PVC plastic is susceptible to sealants containing acid. Corwin recommends you buy non-solvent neutral cure silicone or low solvent poly- urethane. Manufacturers may dictate caulk, but at the least avoid sealants that also break down when exposed to UV rays. The preferred sealants, says Corwin, "won't be the $1.96 tube off the shelf."

Replacement windows are big business. The WDMA estimates 35 million wood, vinyl, metal and clad windows will be changed out this year. Homeowners can expect to pay from $150 to $430 for a standard double hung window. Tack on another $200-$800 per window (including removal of existing windows) for professional installation, estimates Corwin. And it's not a quickie job: even professionals can take six to eight hours to properly install a window.

Recent federal energy legislation offers substantial tax credits to homeowners who install energy saving products, including windows.

Can homeowners do the job themselves?

Absolutely, Corwin said. But you need some skills with carpentry finishing.

"You could do it, but you would need to understand what to do. The question becomes are you going to spend the time it's going to take to get it done right?"