Replacement Windows vs New Construction Windows

by Tony the Window Guy.

In the window business, we frequently use terminology that can be misleading to the lay-person. Two sometimes confusing terms are “replacement windows” and “new construction” windows. I hope to straighten out that confusion here.

Essentially, these terms are used to describe the type of installation method that is used. Let’s start with New Construction.

The best way to describe New Construction would be any window that is going to be installed in a brand new, stud framed rough opening. The wall is “new”, the “rough opening” is new, and the window is “new”. Furthermore, a new construction window is usually a window that has a nailing flange, which is used to secure the window into the new stud framed opening. A metal sill pan is not required if there is a nailing flange all the way around the perimeter of the window, as this fin also acts as a type of “flashing”, which prevents any water from getting into the envelope of the home.

There are some cases, interestingly, where a “new construction” window does not have a nailing flange. In general, in West Coast and especially California construction, windows with nailing flanges are installed into new construction applications. However, it is common in other building markets for windows, particularly Wood Windows, without nailing flanges, to be used in New Construction. In these cases, a sheet metal pan is usually installed on the sill to allow for water to be directed back to the outside of the home. This type of window installation is not very common in California, although it does exist.

A Replacement Window is usually a window that is “replacing” a window that is already existing in a home. There are a number of ways that a replacement window can be installed. One thing that most replacement windows have in common is that they lack a nailing flange. The two most common methods of replacement window installation are: retrofit and block frame.

A retrofit window is a window that is installed over an existing window in a home. In other words, the main frame of the existing window (usually an old aluminum or steel framed window) is left in the wall, and a new, usually vinyl window is installed over it. The operable vent and fixed glass of the existing window are removed, as well as any vertical or horizontal dividers, and the new vinyl window is “retrofitted” into the old window. In this case, the retrofit window has an exterior “fin” that covers the old window from the exterior. New trim is used on to finish of the interior for a clean look.

A block frame window is often used in an old wood sash opening. The old wood sashes are removed, leaving the exising old wood window frame. Then, a new vinyl or wood window, without any nailing flange is inserted into the old wood window frame. This type of installation usually requires some type of a sloped sill adapter, as old wood windows usually have a sloped sill.