Window Glossary of Terms
Acrylic: Thermoplastic glazing material.
Air-Barrier: That part of a wall assembly that prevents passage of air.
Air-Sealed: The application of material (usually a membrane or caulking type sealant) to a wall assembly that results in preventing air passage through the assembly.
Air Infiltration: Air movement through the building envelope. In the case of windows 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)
Apron: Trim moulding fastened below the stool or sill of a window that covers the space between the window sill and the rough sill or window opening sill.
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.
Argon: An inert, non-toxic gas used in insulating glass units to reduce heat transmission.
Astragal: Center post between two swinging doors.
Awning: Window with sash swinging outward from bottom.
Backer Rod: Ropes or Rods made of round flexible and compressible material that can be fit into a gap between two adjacent building components before applying caulking. For best results caulking should not bond with backer rod.
Balance: Mechanical device (normally spring loaded) used in single- and double-hung windows as a means of counterbalancing the weight of the sash during opening and closing.
Bay Window: A combination of window units that project to the exterior. Usually features a large center unit with two flanking units at 30 degree or 45 degree angle to the wall.
Bow Window: 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 project to the exterior. Usually features a large centre unit with two flanking units at 90 degree angles to the wall.
Bracket Support for a Bay or Bow Window: A rigid support fastened to the wall below a bay or bow window that supports that portion of the weight of the window not supported by the sub-sill.
Brick mould: A type of external casing for windows and doors.
Butt edge: The thicker bottom edge of a piece of beveled siding.
Cable support: A method of support for a bay window. Two steel cables (or rods) fastened at the seat of the window, pass through the space hidden by the mullion covers to a truss or rafter above the window, where they are secured thus carrying the portion of the weight of the window not supported by the sub-sill.
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: Generally, a material combining an organic material, such as wood fiber, extruded with plastic.
CCMC (Canadian Construction Materials Centre) http://irc.nrc-cnrc.gc.ca/ccmc/home : An office of the National Research Council that evaluates building materials.
CMHC (Canadian Mortgage and Housing Centre) www.cmhc.ca: Canada’s housing agency, mortgage insurance, housing data, housing research
CSA International www.csa-international.org: A standard writing and certification association.
CRF: Condensation Resistance Factor. A rating of window’s ability to resist condensation. The higher the CRF, the less likely condensation is to occur.
Cladding: Another term for siding. A thin material made of vinyl or aluminum, fitted over wood sash and/or frame members of a window for weather protection and finish color.
Celestory: A window in the upper part of a high-ceilinged room that admits light to the center of the room.
Combination door: A screen or storm door used in combination with a primary door. Storm windows also are referred to as combination windows.
Comfort Temperature: A room is considered comfortable for occupants when the sum of ambient room temperature and adjacent wall/window temperature equals 42 degrees Celsius.
Example: In cold weather conditions the inside glass temperature in a sunroom may fall well below 21 degrees Celsius. To maintain comfort the air temperature in the room would have to be raised one Celsius degree above 21degrees for every Celsius degree drop in the temperature of the glass.
Composite: A term used for window or door components that consist of two or more materials, such as glass fibers or wood and plastic. The term also is used for windows and doors that combine two or more materials in the frame or sash construction, such as products with a wood interior and vinyl or aluminum exterior.
Complete-Tear-Out Window Installation: A method of installing a replacement window where the older window is completely removed back to the original window opening (RSO).
Condensation: Water vapor from the air deposited on any cold surface that has temperature below the dew point.
Conduction: The movement of heat through a solid.
Convection: The movement of heat by way of air movement.
Curved-Top: A term used to describe a window with a curved frame. These units, also called arch-top or round-top 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. Usually specified as one-and-a-half times greater than necessary based on expected building, wind and weather conditions.
Divided lites: Separately framed pieces or panes of glass. A double-hung window, for instance, often has several lites divided by muntins in each sash. These designs are often referred to as six-over-six, eight-over-one, etc., to indicate 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 rood of a house, generally featuring one or more windows.
Door Skin: A single sheet of material used as the face of a door.
Door Slab: A complete door panel that has not been assembled into a frame.
Double glazing: Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits. May or may not refer to an insulating glass unit.
Double-hung Window: Window featuring two operable sash that move vertically in the frame.
Drain hole: Located on the lower outside part of the sill of a window. Drain hole(s) provide an escape route for any rain water that may enter a window.
Drip Cap: A flashing of metal or vinyl placed above a wall opening (eg: door or window) designed to shed rain water 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 U.S. building codes require each bedroom of a home to have an emergency exit window, with minimum size specified.
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. ER numbers range from 0 to over 40. The higher the ER number the better the energy performance.
Energy Star for Windows: www.energystar.gc.ca: A program sponsored by Natural Resources Canada. Energy Star qualifies windows that meet minimum energy performance criteria.
Extrusion: The process by which material is forced through a die to produce lineal profile building components. Eg: vinyl siding, window profiles.
Fascia board: Piece of lumber fastened to the ends of roof rafters.
Fascia capping: Pre-finished metal or vinyl material fastened over the fascia board.
Fibreglass: Building material made of glass fibres and resin. Used to make door slabs, door frames and window frames and sash.
Fixed lite: 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 rain water 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 sash fit(s) inside the window frame.
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.
Grille: 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. Also can be fitted inside the sealed insulated glass unit, when it also is referred to as a grid.
Hard-coat glass: A glass product that is coated during the manufacturing process at the molten glass stage. Also known as a pyrolytic coating. The other type of glass coating is a sputter-coat which is applied in a secondary process, sometimes referred to as soft-coat.
Head: Main horizontal frame member at the top of a window or door.
Header: 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. Also know as a lintel.
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 inside to outside 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.
Hygrometer: A device for measuring the relative humidity of air.
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.
IGMA: (Insulating Glass Manufacturers Association) : This association of insulating glass manufacturers tests and certifies the quality of glass units produced by the members of the association.
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 and security, as well as sound reduction.
Level: When a part of a structure is in a plane that is at right angles to the earth’s gravitational force it is said to be level.
Lintel: A structural component or beam above a window or door opening that supports the wall above. Also referred to as a header.
Lite: A piece of glass. In windows and doors refers to separately framed panes of glass (as well as designs simulating the look of separately framed pieces of glass). Sometimes spelled “light.”
Low-emissivity Glass (Low E): A coated glass product that reflects heat.
Low-E Detector: An electronic device that detects the existence of a low-emissivity coating. This device will identify the surface in an insulated glass unit where the Low-e coating exists.
MDF: Medium-density fiberboard. 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. Generally refers to components used to construct divided lite grids or grilles simulating a divided lite lock.
Nailing Fin: A thin leg extending beyond the outside surface of a window frame. A nailing fin covers the space between the window and the window opening in the wall. A nailing fin provides temporary fastening of a window. Permanent fasteners pass through window jambs at shim locations.
Nailing Hem: The edge of a siding panel designed for fastening of the panel to the wall. Usually has nailing slots and is usually covered by the next siding panel to be installed.
Nailing Slot: The punched-out part of a nailing hem (material removed) for the purpose of fastening a siding panel.
NFRC: National Fenestration Rating Council. A body that has established methods for rating and certifying the energy performance of windows, doors, skylights and other fenestration products.
Picture Window: Large, non-operating window. It is usually longer than it is wide to provide a panoramic view.
Plumb: When a part of a structure is in the same plane as the earth’s gravitational force it is said to be plumb.
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.
PVC (polyvinylchloride): A thermoplastic material used for building components. (eg: siding, soffit, fascia, rain gutter, window and door profiles)
Pyrolytic Glass: see- hard coat glass
Radiation: The transfer of heat and/or light energy through the atmosphere.
Rail: Horizontal member of the framework of a window sash or door.
Rain Screen: Walls and windows must shed rain water. Rain screen describes a wall or window design that provides two rain water shedding surfaces. The second shedding surface acts as a back-up to the primary shedding surface by draining any water that penetrates the primary surface.
Reflective glass: Window glass coated to reflect visible light and solar radiation striking the surface of the glass.
Relative Humidity: A measurement of the amount of water vapour in air at a certain temperature relative to fully saturated air at the same temperature. Expressed as a percentage.
Removal tool (zipper tool): A piece of spring metal with a wood handle on one end and a small hook on the other. This tool is used to hook or grab the butt lock on a siding panel. Used when fitting siding around windows or when removing a panel.
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.
Rough Opening (RSO): Opening in a wall into which a window or door is installed. In wood frame construction this opening is often called the RSO (rough stud opening).
Round-top: One of several terms used for a variety of window units with one or more curved frame members, often used over another window or door opening.
R-value: Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value. R-value is reciprocal of 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, usually inserted into a sash profile prior to assembly, designed to increase the strength of the unit.
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.
Shim(s): Structural support for the installation of windows or doors. Tapered cedar shims are used in pairs. Stacking-type plastic shims are also used for this purpose. Proper shimming and fastening is critical for good window and door performance.
Sidelites: Narrow fixed units mulled or joined to operating door units to give a more open appearance.
Siding: Panels fastened to the outside of a wall to provide an attractive weather resistant finish to the wall.
Sill: The main horizontal member forming the bottom of the frame of a window or door.
Sub-sill: The frame member at the bottom of a window opening that carries the weight of the window.
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, but 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.
Snap-lock Punch: A tool used to raise a series of tabs along the cut edge of a panel of siding. These tabs connect with a finish trim to hold the finishing panel of siding in place.
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. An STC rating is determined by measuring the sound transmission over a selected range of sound frequencies. The higher the number, the less sound transmitted.
Square: When two parts of a structure are situated at right angles (90 degrees) to one another they are said to be square.
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: A moulding used to hold, position or separate window or door parts. Also, the moulding or component on the inside of a window frame against which the window sash rests or closes. Also called a bead, side stop, window stop and parting stop.
Strapping: Wood lumber (usually 1 x 3) fastened to a wall (usually vertically at 16 inch centres) that provides an air space between siding and underlying wall and provides a means of fastening siding panels.
Swiggle: Swiggle is an outdated thermal spacer widely used in the late 80’s early 90’s. it is no longer used due to the high number of seal failures.
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.
Tansom: 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.
U-factor or U-value: Rate of heat flow-value through a building component. U-factor is the reciprocal of R-value.
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. (see PVC)
Vinyl Council of Canada: A division of the Canadian Plastics Institute Association focused on issues relating to PVC.
Vinyl Siding Institute (VSI): An association of vinyl siding manufacturers.
VSI Vinyl Siding Installation Certification: A training program for vinyl siding installers.
Warm-edge: A type of insulating glass construction using an airspacer 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 (drain hole): A small opening in a window sill or a small opening placed every few inches along the butt edge of a siding panel through which water may drain to the exterior.
Wind load: Force exerted on surface by moving air.