Glossary of Terms

Apron: Inside trim moulding used under the stool at the bottom of the window.
Astragal: The center exterior member, used to cover the gap between double doors/windows. It is generally attached to the fixed panel.
Integral Astragal: Astragal milled directly into the sash of the double windows or doors.
top

Bay window: A group of three or more windows, usually composed of a large center unit and two side units at 30°, 45° or 90° angles to the wall.
Bow window: A group of four or more window units in a radial or bow arrangement.
Brick mould: Casing around the outside of a window to cover jambs.
top

Casing: Inside casing is a flat, decorative moulding which covers the inside edge of the jambs and the rough openings between the window unit and the wall.
Circlehead: A generic term referring to any of a variety of window units with one or more curved frame members, often used over another window or door opening.
Cripples: The short 2" x 4" members used to frame under the sill or above the header in a rough opening for a window in a frame wall.
top

Dormer: A space which protrudes from the roof, usually including one or more windows.
Double rafter: The doubling (side by side) of the roof members to reinforce an opening in the roof for a slope glazing installation.
Double glazing: Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
Drip cap: A moulding placed on the top of the head brickmould or casing of a window frame.
Drip edge: The edge of the metal flashing intended to shed water over the edge of the surface being protected.
top

Fenestration: An architectural term referring to the arrangement of windows in a wall.
Finger-jointing: A means of joining individual pieces of wood together to form longer lengths. The ends of the pieces are machined to form a set of interlocking fingers, which are then coated with adhesive and meshed together under pressure.
Fixed: Non-venting or non-operable.
Flashing: A metal strip attached to the outside of the head or side jambs to provide a weather barrier, preventing leakage between the frame and the wall.
top

Gasket: A pliable, flexible continuous strip of material used to affect a watertight seal between sash and frame of roof windows much like the seal around a refrigerator door.
Glazing: The glass panes or lights in the sash of a window. Also the act of installing lights of glass in a window sash.
Glazing stop: The part of the sash or door panel which holds the glass in place.
top

Head: The main horizontal member forming the top of the window or door frame.
Head board: A flat board cut to fit the contour of a bow or bay window and installed between the head jambs and the flat wall surface to finish off that area which would normally be ceiling.
Header: A heavy beam extended across the top of the rough opening to prevent the weight of wall or roof from resting on the window frame.
Hopper: A window with a top sash that swings inward.
top

Integral Astragal: Astragal milled directly into the sash of the double windows or doors.
top

Jack stud: Framing members, generally 2x4s or 2x6s, which form the inside of the window or door rough opening. They run from the sole plate to the header, which is supported by them.
Jamb extender: A custom jamb milled to accomodate a specific wall situation.
top

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 film or metallic coating on the glass or suspended between the two lights of glass to restrict the passage of radiant heat.
top

Masonry openings: The opening in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall.
Mortise: A slot or rectangular cavity cut into a piece of wood to receive another part.
Mortise-and-tenon: A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other.
Mullion: The vertical or horizontal divisions or joints between single windows in a multiple window unit.
Mullion casing: An interior or exterior casing member to cover the mullion joint between single windows.
Multi-point Locks:Multiple locks around the frame of the window or the door. Also referred to as perimeter hardware.
Muntin: A short bar used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.
top

Palladian window: A large, arch-top window flanked by smaller windows on each side.
Panel: Usually refers to the separate panel or panels in a door frame.
Perimeter Hardware: Hardware which wraps around the window or door providing tilt function as well as locking around the window.
Perimeter Locks: Additional lock points around the sash of the window or door, keeping the sash weather-tight all arround.
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. Also know as full-bound casing.
Pivot: A mode of operation for ventilating windows which generally means the sash pivots on a central axis and turns 90 or more degrees.
top

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 member, usually two inches by four inches, which forms the bottom of the rough opening. It is toe-nailed into the jack studs and is supported by cripples.
top

Sash: The operable "frame" of the window inset in the main window frame. Door "sash" is often referred to as the panel.
Sash lock: The piece of hardware that pulls the sash tightly to the frame, both for security and weathertightness.
Seat board: A flat board cut to fit the contour of a bow or bay window and installed between the sills and the flat wall surface, providing a seat or shelf space.
Shims: Wood wedges (often wood shingles) used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation.
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. Often divided into the Exterior and Interior sill.
Sill course (soldier course): The row of brick, cement blocks or stones laid across the bottom of a masonry opening, which lie under the outside edge of the window sill.
Simulated divided light: A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulating glass to simulate the look of true divided light. Glass spacer is also used to give the impression of divided glass panes.
Single glazing: Use of single panes of glass in a window. Not as energy-efficient as double glazing.
Solar gain: The process of providing a net heat gain within a structure, over and above the normal heat loss, by passive collection of the sun's heat through windows and other glazed areas.
Sole plate: The bottom horizontal member in a frame wall. Usually either single or double 2x4s. It is nailed to the deck or rough floor and the studs are nailed into it.
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 hold, position or separate window parts. The stop is often moulded into the jamb liners on sliding windows.
Stud: Vertical wood framing members which form a frame wall. In regular construction these are eight foot-long 2" x 4"s.
top

Tenon: A rectangular projection cut out of a piece of wood for insertion into a mortise.
Transom: A smaller window above a door or another window. A transom joint is also the horizontal joining area between two window units which are stacked one on top of the other.
Triple glazing: A sash glazed with three lights of glass, enclosing two separate air spaces.
True divided light: A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins.
top

U-Factor: A measure of heat transmission through a wall or window. The lower the U-factor, the better the insulating value. R-value is calculated as R = 1/u-value.
top

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.
top