Interior Window Casing Terminology

Stool

• The window stool is the horizontal piece of frame across the bottom of the window. You may be more familiar with the term sill. A window sill is the term a layman would most likely use, but a builder would say window stool. When the glass part of the window is closed, it sits on top of the stool.

Apron

• A window apron is also located underneath the bottom of the window frame. An apron is a piece of wood, usually of decorative molding that is installed at the base of the window stool or sill. The apron gives the window its finished look. The apron should sit up against the wall when properly installed. The apron is normally the last piece of the window casing that is attached. There should be no gaps between the apron and the stool.

Jamb

• While you may be familiar with a door jamb, a window jamb sounds less familiar. A door jamb and a window jamb serve the same purpose. The jambs are the flat pieces that actually frame the window casing. There is a head jamb, which goes across the underside of the frame at the top of the window. There are also two side jambs, which frame the sides of the window casing. The jambs are installed flush with the actual wall. The jambs must be straight or they can impede the raising and lowering of the window.

Mantle

• A fireplace mantle goes over the fireplace and often gives it a decorative look. The same is true of the mantle of the window casing. The mantle is usually a piece of decorative molding, but it can also be installed so that it leaves a little bit of a shelf across the top of the window.