What is the difference between replacement and new-construction windows?
Short Answer
The installation method and amount of surrounding assembly modification can differ. The correct choice depends on existing frame, exterior finish, flashing, wall condition, and project scope.
Detailed Explanation
New-construction windows have a nailing fin (flange) around the perimeter that's nailed to the exterior wall sheathing. They're typically installed during new construction or when the siding is being removed, because the fin needs to be accessible and integrated with the weather-resistive barrier. Replacement windows (also called insert or pocket windows) are designed to be installed within the existing window frame — the old sash is removed and the new window slides into the existing frame. This is less invasive and less expensive, but it doesn't allow access to the flashing or weather-resistive barrier. If the existing frame is in good condition and the wall assembly is sound, replacement windows can work well. If the frame is damaged or the flashing needs attention, new-construction windows (installed from the exterior) provide better access for proper water management.
Why It Matters
Choosing the wrong window type can compromise water management or result in unnecessary expense. The decision depends on the condition of the existing frame and wall assembly.
When Repair Makes Sense
Existing window frame is in good condition and only the sash needs replacement — replacement windows are appropriate.
When Replacement Makes Sense
Existing frame is damaged, flashing needs replacement, or siding is being removed — new-construction windows provide better access and integration.