Window Glossary

Acrylic: Thermosplastic glazing material.

Air Infiltration: Air movement between a window sash and frame; it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through. The CSA A440 standard for windows, the “A” measurement rates air infiltration.

Aluminum: A light weight metal used for building components. (eg: siding, soffit, fascia, capping coil, rain gutter, window profiles)

Air Latch: Latch mechanism on the interior face of the sash that retains the window in a partially open position for ventilation.

Angled Exterior: A sloped extension from the frame that adds an aesthetically pleasing dimension to the exterior of the window.

Arch-Top: A term used to describe a window unit with a curved frame. These units, also called curved-tops or round-tops are often placed over another window.

Air Chambers: Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window

Argon: An inactive, non-toxic, odorless, colorless, non-flammable inert gas used in insulating glass units to reduce heat transmission.

Astragal: Center post between two swinging doors.

Awning: Window with sash swinging outward for ventilation from bottom.

Balance: Mechanical device (usually spring loaded) used in single and double hung windows as a means of counterbalancing the weight of the sash during opening and closing.

Bay: A combination of window units that projects to the exterior. Usually features a large center unit with two flanking units at 30 degree or 45 degree angle to the wall.

Beveled Exterior: An angled extension from the frame that adds an aesthetically pleasing dimension to the exterior of the window.

Block frame window: Used when replacing the wood sash of an old double hung wood window.
Bow: A combination window that projects to the exterior. Usually features four or more window units in a radical or bow formation.

Box Bay: A combination of window units that projects to the exterior. Usually features a large centre unit with two flanking units at 90 degree angles to the wall.

Brockmould: A type of external casing for windows and doors.

Capping: A thin covering material, of metal or vinyl that is fitted over another building component for weather protection and finished appearance. Also used as a flashing to prevent rain water penetration.

Capstock: A material co-extruded with PVC formulated to offer a specific color, finish and/or function, such as heat resistance.

Casement: Window with sash cranking outward, to the right or left.

Casing: Exposed moulding or profile around a window or door, on either the inside or outside, to cover the space between the window frame or door jamb and the wall.

Caulking: A compound for filling joints and sealing cracks to prevent leakage of water and air.

Cellular PVC: Extruded polyvinyl chloride material used in window and door components and trim. Unlike rigid vinyl, it features a foam or cell-structure inside. It can often be nailed, sawn and fabricated like wood.

Cellulosic composite: A material combining an organic material like wood extruded with plastic.

Condensation Resistance Factor (CRF): A rating of window’s ability to resist condensation. The higher the CRF, the less likely condensation is to occur.

Cladding or Siding: A thin material made of vinyl or aluminum, fitted over wood sash and/or frame members of a window for weather protection, durable low maintenance finish color.

Clerestory: A window in the upper part of a high-ceilinged room that admits light.

Combination door: A screen or storm door used in combination with a primary door. Storm windows also are referred to as combination windows.

Composite: Window or door components that consist of two or more materials, such as glass fibers or wood and plastic. Another example is two or more materials in the frame or sash construction, such as products with a wood interior and vinyl or aluminum exterior.

Condensation: Water vapor from the air deposited on any cold surface that has temperature below the dew point.

Curved-Top / Coved Exterior / Arch-top / Round-top: A term used to describe a window with a curved frame. These units are often placed over another window.

Desiccant: A material used to absorb moisture from within the sealed airspace of an insulation glass unit.

Design pressure (DP): A measurement of the structural performance of a window or door.

Divided lites (examples six over six, eight over one): Separately framed pieces or panes of glass. It indicates the number of lites in each sash. (Designs simulating the appearance of separately framed panes of glass are often referred to as SDLs or simulated divided lites. Designs using actual separate pieces of glass are sometimes referred to as TDLs or true divided lites.)

Dormer: An area that protrudes from the roof of a house, featuring one or more windows.

Double glazing: Use of two panes of glass in a window to increase energy efficiency and other performance benefits.

Double-hung Window: Window featuring two operable sash that move vertically in the frame.

Drip Cap: A flashing of metal or vinyl placed above a door or window to shed rainwater away from the wall of a building.

Egress window: Window designed to be large enough for a firefighter to climb in or a person to climb out of in an emergency.

Energy Rating (ER): A measure of the thermal performance of a window. A window’s air infiltration and solar heat gain are used to calculate that window’s ER. The higher the ER number (zero to forty range) the better the energy performance.

Energy Star for Windows: A program sponsored by Natural Resources Canada. Energy Star qualifies windows that meet minimum energy performance criteria.

Fixed lite / Fixed window / Picture window: Non-venting or non-operable window.

Fixed panel: Non-operable door usually combined with operable door unit.

Flashing: A strip of metal or vinyl that diverts rainwater away from a wall or roof assembly.

Fogging: If a sealed glazing unit fails the moisture or the residue from evaporating moisture that collects on the inside surfaces is called “fogging.”

Frame: The main structural element of window composed of two vertical side jambs and two horizontal components called a head and a sill. The window frame encloses the window sash.

French door: Generally refers to a pair of hinged doors that open from the middle.

Garden Window: A window that projects beyond the outside surface of the adjacent wall. These windows are designed to accommodate the growing of potted plants.

Glazing: Glass (and other material) in a window or door. Also, the act or process of fitting a unit with glass.

Glazing stop: A component of the sash or door panel that holds the glass in place.

A term referring to window dividers or muntins. It may be a type of assembly fitted to the interior of the window or door unit that can be detached for cleaning.

Hard-coat glass / Pyrolytic coating: A glass product that is coated during the manufacturing process at the molten glass stage. The other type of glass coating is a sputter-coat or soft-coat which is applied in a secondary process.

Head: Main horizontal frame member at the top of a window or door.

Header or Lintel: Horizontal framing member placed over the rough opening of a window or door to prevent the weight of a wall or roof from resting on the frame.

Heat Gain: The transfer of heat from outside to inside by means of conduction, convection and radiation through all surfaces of a house.

Heat Loss: The transfer of heat from outside to inside by means of conduction, convection and radiation through all surfaces of a house.

Hopper: Window with sash that swings inward from the top.

Horizontal Slider: A window with a movable sash that slides horizontally.

Insulating Glass (IG): Two or more lites of glass with a hermetically sealed airspace between the lites. The sealed space may contain air or be filled with an inert gas, such as argon.

Jamb: Main vertical members forming the sides of a window or door frame.

Jamb Depth: Width of a window or door from the interior to the exterior of the frame.

Jamb Extension: A piece added to the jamb of a window (also head and sill) to make the depth of the window fit the wall thickness.

J-Channel: Trim for siding used primarily at the sides of windows and doors.

KD (Knocked down): Unassembled window or door.

Laminated Glass: Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for enhanced safety, security, and sound reduction.

Lintel / Header: A structural component or beam above a window or door opening that supports the wall above.

Lite: A piece of glass or separately framed panes of glass.

Low-emissivity (Low E): A coated glass product that reflects heat.

Medium-density fiberboard (MDF). A wood-fiber composite used in a variety of window, door and millwork applications.

Mortise lock: A lock fitting a rectangular-shaped cavity in the edge of a door.

Mullion: A component used to structurally join two window or door units.

Multipoint lock: A locking system, operated with one handle that secures a window or door at two or more locking points.

Muntin: Profile or moulding, either vertical or horizontal, used to separate glass in a sash into multiple lites.

Nailing fin: A thin leg extending beyond the outside surface of a window frame that covers the space between the window and the window opening in the wall. Permanent fasteners pass through window jambs at shim locations.

Picture window: Large, non-operating window that is longer than it is wide to provide a panoramic view.

Polycarbonate: A plastic material used for glazing.

Pre-hanger: A company that buys doors, framing, hardware, glass lites and other components, and prepares (or pre-hangs) the unit for installation.

Prime window: A primary window, as opposed to a storm or combination unit added on.

Pultrusion: The process used to produce fiberglass composite profiles or components for the production of windows and doors.

Polyvinylchloride (PVC): A thermoplastic material used for building components. (example siding, soffit, fascia, rain gutter, window and door profiles)

Rail: Horizontal member of the framework of a window sash or door.

Reflective glass: Window glass coated to reflect visible light and solar radiation striking the surface of the glass.

Retro-Fit Window Installation / Insert window: A method of installing a replacement window inside the frame of an older wood window.

Replacement Window: Any window custom made to replace an older window.

Roof Window: An operable unit similar to a skylight placed in the sloping surface of a roof.

Round-top: A window unit with one or more curved frame members, often used over another window or door opening.

R-value / U-factor: Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value. Similar to the U-factor or rate of heat flow.

Safety glass: A strengthened or reinforced glass that is less subject to breakage or splintering and less likely to cause injury if broken.

Sash: An assembly of stiles and rails (vertical and horizontal members) made into a frame for holding glass.

Sash cord: Rope or chain in double-hung windows that attached the sash to the counter balance.

Sash lift: Protruding or recessed handle on the inside bottom rail of the lower sash on a double- or single-hung window.

Sash stiffener: A reinforcement to increase strength of window unit, usually inserted into a sash profile prior to assembly.

Sash weights: Concealed cast-iron weights used to counterbalance the sash of older double-hung windows.

Self-cleaning glass: Glass treated with a special coating. Currently, commercially available products feature a coating that uses the sun’s UV rays to break down organic dirt through what is called a photocatalytic effect. The coating also provides a hydrophilic effect, which reduces the surface tension of water to cause it to sheet down the surface easily and wash away dirt.

Sidelites: Narrow fixed units mulled or joined to operating door units to give a more open appearance.

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

Sill pan: A product placed under a window or door during the installation process that is designed for water drainage.

Simulated divided lites (SDLs): A type of grille or grid design that created the appearance of a number of smaller panes of glass separated by muntins. It actually uses larger lites of glass with the muntins placed between and/or on the surfaces of the glass layers.

Single glazing: Use of a single lite of glass in a window. Not as energy efficient as insulating glass or other forms of double glazing.

Single hung: A window resembling a double-hung, or vertically sliding window, with a fixed top sash.

Soffit: Material running from the back of the fascia board to the wall, usually made of plywood, vinyl or aluminum. Soffit is often vented to allow air movement into the space under the roof.

Solar-control glass: Glass produced with a coating or tint that absorbs or reflects solar energy, thereby reducing solar gain.

Solar Heat Gain Coefficient (SHGC): A measurement of a window’s ability to transmit solar energy. The lower a window’s SHGC the less solar energy it transmits.

Soft-coat glass: A glass product that is coated in a secondary process known as sputter-coating, usually to offer low-emissivity or solar-control benefits. Hard-coat or pyrolytic glass is coated during the manufacturing process at the molten glass stage.

Sound transmission class (STC): A rating measuring a window’s acoustic properties or its ability to reduce sound transmission. It is determined by measuring the sound transmission over a selected range of sound frequencies. The higher the number, the less sound transmitted.

Stile: The main vertical frame members of a sash or door.

Stool: Interior trim piece sometimes used to extend a window sill and act as a narrow shelf.

Stop / Bead / Side stop / Window stop / Parting stop: A moulding used to hold, position or separate window or door parts.

Tempered glass: Glass heat-treated to withstand greater than normal forces on is surface. When it breaks, it shatters into small pieces to reduce hazard.

Thermal break: A thermally insulting or low-conductance material used between interior and exterior aluminum (or other conductive material) window and door components.

Tilt window: A single- or double- hung window whose operable sash can be tilted into a room to allow cleaning of the exterior surface on the inside.

Transom: A small window used over the top of a door or window, primarily for additional light and aesthetic value.

Triple glazing: Use of three panes of glass or plastic with two airspaces between. Generally refers to a sealed insulating unit.

True divided lites (TDLs): Traditional window construction incorporating smaller panes of glass actually separated by muntins, rather than simulating such an appearance with larger lites of glass and a muntin grid or grille placed between or on the surfaces of the glass layers.

Ultraviolet light (UV): Invisible rays of solar radiation at the short-wavelength end of the spectrum. Ultraviolet rays can cause fading of paint finishes, carpets and fabrics, as well as deterioration of some materials.

Vinyl: Generic term for polyvinylchloride or PVC.

Warm-edge: A type of insulating glass construction using an air spacer offering lower thermal conductance than traditional aluminum spacer. Warm-edge IG units typically offer higher resistance to condensation and an incremental improvement in window energy performance.

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

Weep hole: Small opening in a window or sill member through which water may drain to the building exterior.

Wind load: Force exerted on surface by moving air.

Images from CMHC, Jeld-Wen windows (we are a certified installer), and CH&H magazine. Colour collection from Kaykan; F&B colour wheel. Window Glossary from a collection of window resources and websites.