Home Improvement Glossary

Astragal
The center member of a double door, which is attached to the fixed or inactive door panel.

Infiltration
In the winter, warm air leaks out and cool air leaks in. This process reverses itself in the summer.

Jamb
The main vertical members forming the sides of a window or door frame.

Light
A separately framed piece of glass in a window or door. A traditional double-hung window, for instance, often has several lights divided by muntins in each sash. Such windows are described as six-over-six, eight-over-one, twelve-over twelve, etc., to indicate the number of lights in each sash. Sometimes spelled 'lite.'

Mortise
A slot in a masonry wall left open for windows or doors.

Mullion
A wood or metal part used to structurally join two window or door units.

Muntin
Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.

Panel
Usually refers to the separate panel or panels in a door's frame.

Sidelights
Narrow fixed units mulled or joined to door units to give a more open appearance.

Sill
The main horizontal member forming the bottom of the frame of a window or door.

Weather Stripping
A material or device used to seal the openings, gaps or cracks of venting window and door units to prevent water and air infiltration.

Extrusion
A form produced by forcing material through a die. Window frames are constructed of either vinyl or aluminum extrusions