Apron: Inside flat trim member, which is used under the stool at the bottom of the window.
Awning window: A window that has a single sash in which the bottom of the sash swings out.
Astragal: The center member of a double door, which is attached to the inactive door panel.
Bay window: Three or more windows in a row, usually made up of a large unit in the center and one unit on either side at 30°, 45° or 90° angles to the wall.
Bow window: Four or more window units together in a bow formation.
Brick mould: Outside moulding around the window frame to cover jambs.
Casing: Inside casing is a flat, decorative moulding that covers the inside edge of the jambs and the rough openings between the window unit and the wall.
Check rail: On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted.
Dormer: A space, which protrudes from the roof, usually including one or more windows.
Double-glazing: Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
Double-hung: A window with two vertical operating sashes that slide up and down.
Double rafter: The doubling (side by side) of the roof members to reinforce an opening in the roof for a slope-glazing installation.
Drip cap: A moulding placed on the top of the head brick mould or casing of a window frame.
Egress window: A window large enough for exit or entry in case of an emergency.
Fenestration: An architectural term referring to the placement of windows in a wall.
Finger-jointing: A way of joining pieces of wood together to form longer lengths.
Fixed: Non-venting or doesn’t open.
Flashing: A metal or plastic strip attached to the outside of the head or side jambs to provide a weather barrier. It prevents leakage between the frame and the wall.
Gasket: A strip of material used to create a watertight seal between the sash and the frame of a window.
Glazing: The glass panes or lights in the sash of a window.
Glazing bead: A plastic or wood strip applied to the window sash around the glass.
Glazing stop: The part of the sash or door panel which holds the glass in place.
Grille: A bar used to visually separate glass into multiple lights. Also called a windowpane divider or a muntin.
Head: The main horizontal member forming the top of the window or doorframe.
Head board: A flat board that fits the contour of a bow or bay window at the top and that finishes off the ceiling inside the window.
Header: A heavy beam extended across the top of the rough opening to help support the weight of the building.
Jamb liner: Metal or plastic covering the inside surface and head jambs of sliding windows.
Keeper: The part of a casement window lock that looks like a hook.
Lift: Handle or grip installed on the bottom rail of the lower sash of a double-hung window to make it easier to raise or lower the sash.
Light: (also spelled lite) Glazing framed by muntins and/or sash in a window or door.
Low-E glass: A common term used to refer to glass, which has low emissivity due to a metal coating on the glass surface between the two lights of glass to restrict the passage of radiant heat.
Masonry openings: The opening in a masonry wall to accept a window or door unit.
Molding: An exterior trim around the perimeter of a frame.
Mortise: A slit cut into a piece of wood to receive another part.
Mullion: The joints between single windows in a multiple window unit.
Mullion casing: An interior or exterior casing to cover the mullion joint between single windows.
Muntin: A bar used to visually separate glass into multiple lights. Also called a windowpane divider or a grille.
Operator: A metal arm and gear, which allows for easy operation or closing of projecting windows.
Outer frame member: The exterior protruding portion of a window frame, which has no exterior casing.
Panel: Usually refers to the separate panel or panels in a doorframe.
Picture frame casing: The use of casing on all four sides of the interior of a window, replacing the stool and apron at the sill.
Pitch: The degree of the slope of a roof.
Rafter: Structural members of a roof that support the roof load.
Rails: The horizontal members of a window sash or door panel.
Rough opening: The opening left in a frame wall to receive a window or door unit.
Rough sill: The horizontal rough framing area which forms the bottom of the rough opening.
Sash balance: A system of weights, cords and/or coiled springs which assist in raising double-hung sash and tend to keep the sash in any placed position by counterbalancing the weight of the sash.
Sash cord: In double-hung windows, the rope or chain that attaches the sash to the counter balance.
Sash lock: A lock applied to the checkrails of a sliding window or at the open edges of a projecting window to pull the checkrails tightly together or to seal the sash tightly to the frame, both for security and weather tightness.
Seat board: A board that fits the contour of a bow or bay window at the bottom and that provides a seat or shelf space.
Shims: Wooden wedges that are used to secure windows in the rough opening. Helps make the window level within the rough opening.
Side lights: Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule.
Sill: Horizontal member that forms the bottom of a window frame.
Sill course: The row of bricks across the bottom of a rough opening.
Simulated divided light: A method of constructing windows in which grilles are attached to the inside and outside of a panel of glass to simulate the look of true divided light.
Single glazing: Use of single panes of glass in a window.
Single-hung: A double-hung type of window in which the top sash is fixed or inoperable.
Solar gain: The readings of how much heat is collected inside a home through the glass of windows and doors.
Stile: The vertical side member of a window sash or door panel.
Stool: Inside horizontal trim member of a window sash or door panel.
Stop: A wood trim member nailed to the window frame to secure window parts in place.
Stud: Wood framing members, used vertically, to build a frame wall. In construction, these are eight-foot-long 2x4's.
Transom: A smaller window above a door or another window.
Triple glazing: A sash glazed with three lights of glass, enclosing two separate air spaces.
U-Factor: A measure of heat transmission through a wall or window. The lower the U-Factor, the better the insulating value.
Vapor barrier: A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.
Venting unit: A window or door unit that opens or operates.
Windload: Force exerted on a surface by moving air.
Windowpane Divider: A short bar used to separate glass in a sash into multiple lights. Also called a muntin or a grille.