What’s the difference between replacement windows and new construction windows?

This is one our frequently asked questions when we’re talking to homeowners about replacing windows in their home and it’s easy to understand why there’s confusion between the two, because there’s quite a lot of overlap between them.

Replacement windows New construction windows
Main use Replacement windows are ideal for situations where the window mechanism (up and down motion) or glass needs replacing but the window frame is in good shape. New construction windows would be used as the name suggests for new construction – either a complete brand new building or within an addition.
Secondary use None Sometimes a window needs to be replaced because both the window mechanism AND the frame are damaged. In this case a new construction window is required.
How installed The existing window is removed and the replacement window is slotted into the remaining hole. Normally this can be done from the inside without any need to rework outside trim. New construction windows are installed from the outside into a bare hole. Trim to finish off the look of the window would need to be added after the window is installed.
Main advantages Cost – replacement windows are generally always less expensive than new construction windows.
Speed – because no exterior work is needed replacement windows can be installed quickly.
Completely weather-tight – because you’re installing one complete unit there’s zero chance of leaks when installed correctly.
Disadvantages Requires professional installation – replacement windows are built to exacting tolerances and are customized for each situation. This means they are not easy to install for the average DIYer. Cost – because you are buying a complete window unit including frame and trim this will almost always be more an expensive option.