An installer applies sealant around the face of a window opening before setting the replacement window.
When a finned unit is trimmed to fit a recessed opening, an equal amount should be removed from each fin to ensure that the unit is centered in the opening.
Before the window is installed, the old window frame gets a 1/2-inch-diameter continuous bead of polyurethane sealant.
Extra sealant pumped into the upper and lower corners prevents water that may have leaked behind the stucco from exiting the wall cavity at the old window frame.
The window is fastened to the wall framing with 3-inch deck screws driven through the jambs; plastic shims prevent the vinyl frames from distorting.
Sealant should be compressed as the window is installed, and tooled after the window is fastened in place, to remove small voids and air bubbles.
With a flush window, applying painter's tape to the wall and window fin gives the sealant a straight edge and speeds cleanup.