Installing windows usually isn't complicated, but it can go wrong when installers fail to pay attention. According to home improvement company owners, the most common mistakes installers make — those that result in botched jobs, callbacks, or a blown referral — include the following:

  • Mismeasuring. Not paying attention accounts for most mismeasures, says David Matus, president of Matus Windows in Philadelphia, because most window openings are fairly straightforward. Mistakes, he contends, “typically result from carelessness in writing down the measurements, or installers being unable to read their own handwriting.” The consequences? “If the measurement isn't right, then you're trying to improvise,” Matus says. And if you're trying to improvise, there's a chance you won't get the window in. More than a chance if your measurements result in a window that's too big.
  • Not double-checking. Jim Brown, owner of Arch Home Improvements, Ashland, Ohio, says taking the old window out before being sure the new one fits could make you look stupid. “People grab the window, thinking it will fit, and tear out the old one,” he says. “If it's too big, you have a problem; besides saying you messed up and having to order another window, you have a hole in the house and must figure out how to get the old window back in.” Brown says that while his crews (company employees) occasionally mismeasure, he “drills it into their heads to make sure that the window is going to go into the hole.”
  • Moving way too fast. Chuck Raysor, co-owner of Exterior Concepts in Middletown, Del., says installers sometimes forget to caulk from outside — “the most important part of the installation.” They also occasionally fail to put enough insulation around the window perimeter. “It happens when the installer's moving too fast and probably lacking material on the jobsite,” Raysor says. The result? Drafts or window condensation.
  • Mishandling window treatments. Make it clear to installers and homeowners who's responsible for window treatments, i.e., curtains, blinds, etc. Michael Sullivan of Lifetime Aluminum Storm Window, in New Jersey, says the company has a policy — made clear at the time of sale and when the job is scheduled — that homeowners are responsible for taking down and putting up window treatments. But there are exceptions. “If it's an elderly couple, or the homeowner literally doesn't own a screwdriver, I make note of it on the installation sheet,” he says.
  • Not being considerate of the property. You can quickly blow a potential referral by leaving paint chips, screws, or other debris lying around. Sullivan suggests using multiple drop cloths, adding that one red flag is sloppy removal of window stops. “Homeowners are usually looking over the installer's shoulder at that stage,” he says. “Carelessness with stops makes every phase of the installation suspect.”