If your home is under construction, the wall materials are probably brand new, and window installation usually proceeds without unforeseen problems. But with an older home, be prepared: "What you don't see is what you get," and if it's one of these four problems, estimates for your window installation cost could be off.
With replacement windows, one or more of your existing windows may suffer from the following expense-boosters.
Size deviations: With the old window removed, the opening can be too large, too small, or too out of plumb for the new window. Shims can be a quick, cheap fix if a window is out of plumb, but a size problem may require reframing the window opening. A contractor often can't tell this in advance, unless you are specifying a noticeable size change. In getting bids for the installation job, you may wish to have the contractor include a contingency fee per window for correcting unknown size problems. Also specify that the new framing is tightly insulated. An Energy Star window in a leaky frame can decrease some of your monthly savings.
Mold: Too much moisture inside and/or outside your home can create mold, which can in turn create health risks. There's no point in replacing a window until all mold damage, and the sources of excess moisture, are addressed. Using bleach on mold is counter-productive. Hire a mold remediation company before installing new windows. A dehumidifier or improved ventilation may be necessary in high-humidity rooms or climates. Cost will depend on how much work needed.
Dry rot: If dry rot is extensive, the contractor typically has to cut away damaged wood and replace it. If it's in small pockets, he can clean out the pocket and fill it with a hard-drying epoxy.
Invasive pests: Termites and carpenter ants may have created tunnels and cavities underneath your old windows. Termites often leave very tiny pyramids of droppings on your window sills, furniture or hard floors. Carpenter ants look for household food and may be seen foraging by evening or night. Call an exterminator, and be sure to keep wood, alive or cut, well away from your house and foundation. Install new windows after extermination is complete.
Many homes have none of the above problems and installation is a straightforward task. Very rough replacement window cost for a plain 3-by-4.5-foot-high Andersen double-hung window varies from around $600 for their very best 400 Series to around $300 for their 200 series. An uncomplicated window installation can run roughly $200 and up.