How to Replace Windows on a House

Choose replacement windows. The manufacturer of the new windows will determine how to measure your existing windows to choose the appropriate replacement-window dimensions. Some manufacturers require measuring the rough opening, while others request measurements of the existing windows themselves.

Measure the height and width as designated by the manufacturer. Take three separate measurements of each height and width. For height, measure from the left, middle and right; when measuring width, measure along the top, middle and bottom of the window. Use the smallest measurement of the three.

Before removing your existing windows, examine the new windows, making sure they are the correct size and free of damage.

Remove both interior and exterior window trim by cutting existing caulk and paint with utility knife, then carefully use a pry bar to loosen and remove. Saw between window frame and rough framing, cutting the nails and screws holding the window in place. You may also opt to remove the window sashes for easier handling, or you can pull out the entire window and frame at once.

Place the new window in the rough opening from the exterior of the home. Insert shims between the frame and rough opening, and tap them into place. Use a level to ensure the window is level both horizontally and vertically. You may need to combine shims to increase thickness and fill gaps. Center the window with gaps of approximately 1/2 inch or less per side. Per the manufacturer's directions, screw or nail the window frame into place. Trim excess wood from the shims with a saw.

Using a putty knife, place insulation into the gap between the window frame and rough opening. Do not pack the insulation too tightly, which diminishes its effectiveness. For added insulation, apply insulating tape and caulk.

Replace the exterior flashing and trim. On the interior, replace the trim using finishing nails and caulk as needed.