This glossary defines most commonly used window and glass terms.
Architectural shape: A term referring to any variety of window units with either some degree of curved frame or geometric shape.
Bay window: A composite of three or more windows, usually made up of a large center unit and two flanking units at 30°, 45° or 90° angles to the wall.
Bow window: A composite of four or more window units in a radial or bow formation.
Brick mould: Outside casing around window to cover jambs and through which nails are driven to install the window.
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. Outside casing (or brick mould) serves the same purpose, as well as being an installation device through which nails are driven to install the window unit to the wall.
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 brick mould or casing of a window frame.
Fenestration: An architectural term referring to the arrangement of windows in a wall.
Flashing: A metal or plastic strip attached to the outside of the head or side jambs to provide a weather barrier, preventing leakage between the frame and the wall.
French sliding door: A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door.
Glazing: The glass panes or lites in a sash of a window. Also the act of installing lites of glass in a window sash.
Glazing bead: A vinyl or wood strip applied to the window sash around the perimeter of the glass.
Head: The main horizontal member forming the top of the window or door frame.
Head expander: A window accessory that slides over the window head frame and can be adjusted to eliminate any gap between the window head and the rough opening height.
Hopper: A window that is hinged at the bottom and has a top sash that swings inward.
Keeper: The piece of window hardware that engages with the sweep lock to draw the window sashes together to ensure security and proper weatherseal.
Lift rail: A handle or grip extruded on the bottom of the lower sash rail of a double-hung window to make it easier to raise or lower the sash.
Light/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 lites of glass to restrict the passage of radiant heat.
Masonry openings: The openings in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall.
Mullion: The vertical or horizontal divisions or joints between single windows in a multiple window unit.
Muntin: A short bar used to separate glass in a sash into multiple lights. Also called a windowpane divider or grid.
Operator: A metal arm and gear which allows for easy operation or closing of projecting casement windows.
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.
Pivot: A mode of operation for ventilating windows which generally means the sash pivots on a central axis and turns 90° or more.
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.
R-value: A measure of thermal resistance in heat transfer. The higher the R-value of an energy-saving glass package, the higher the insulation value of the window—and the greater comfort and energy efficiency of your home.
Sash balance: A system of coiled springs which assist in raising double-hung sashes and keep the sashes in any placed position by counterbalancing the weight of the sashes.
Sash lock: Generally, a cam-action lock applied to the lock rails of a sliding window or at the open edges of a projecting window to pull the lock and keeper rails together to seal the sash tightly, 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 a 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.
Sill (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 lite: 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.
Single-hung: A double-hung type of window in which the top sash is fixed or inoperable.
Solar heat 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.
Stile: The vertical side member of a window, sash, or door panel.
Transom: A smaller window above a door or another window.
Triple glazing: A sash glazed with three lites 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.
VyCore™ Foam: A low-density, semi-rigid polyurethane foam specifically formulated for vinyl profile windows to enhance a window’s insulation (R-value).
Windload: Force exerted on a surface by moving air.
Put your newfound knowledge to good use: Contact a Vytex dealer for the quality replacement windows you need.