Glossary of Terms
The manufacture and installation of windows and doors is a specialized industry, with its own technical lingo. To help you navigate this website, including some of the manufacturer’s brochures, we’ve put together this glossary of terms. We want you to feel confident in your window and door selection—and in your choice of GEM windows—not confused by technical garbledeegook.
Air infiltration – The amount of air leaking in and out of a building through cracks in walls, windows, and doors.
Argon – A colourless, odourless, non-flammable, non-reactive, inert gas which acts as an insulator between the panes of glass in a sealed unit.
Astragal – The center member of a double door, which is attached to the fixed or inactive door panel.
Awning window – An operating style of window with a sash hinged on the sides, and swings open at the bottom towards the exterior.
Balance – A mechanical device, normally spring loaded, used in hung windows to counterbalance the weight of the sash during opening and closing.
Bay window – A three-unit combination window consisting of central picture or fixed window and flanked by a pair windows set at an angle (usually 45o).
Brickmould – Decorative perimeter or border that encases the entire window and is visible from the outside of the house.
Bow window – A type of window consisting of four or more window units attached at an angle to give the impression of a curve.
Casement window – An operating style of window with a side-hinged sash that opens from the side towards the exterior.
Casing – Molding of various widths, thicknesses and shapes applied to the framework of window and door units.
Caulking – A sealant used to seal construction joints, in order to prevent water and air infiltration.
Cladding – A material—usually aluminum—locked to the outside faces of many products to provide a durable, low-maintenance exterior surface.
Combination window – A combination of two or more complete window assemblies of the same or different types that are mulled together.
Condensation – Moisture formation on surfaces due to cold temperatures, high humidity levels and poor air flow.
Conduction – A process of heat transfer whereby heat moves directly through a material by molecule agitation.
Dew point – The temperature at which water vapour will condense as warm, moist air is cooled.
Double hung window – An operating style of window with an upper sash that slides down and a lower sash that slides up.
Drip cap – A moulding placed on the top of the head brickmould or casing of a window frame.
Dry glazing – A method of securing glass in a window frame with a dry, preformed, resilient gasket, without the use of a glazing component.
Double pane (Double glazed) – An insulated glass unit consisting of two panes of glass held together by a sealant and a spacer bar.
Edge of glass – The area within 10 cm (2.5 in) of the edge surrounding the perimeter of the glass.
Egress – The space in which the operating part of the window requires clearance for fire regulations.
Elliptical window – Curved top window that does not form a half circle, since the curvature is less. The arch doesn’t come down to the sill, but meets with vertical sides.
Emissivity – The rate at which a surface of a material radiates long-wave heat energy, usually referring to glass surface properties. Low emissivity results in less overall heat loss.
Extension jambs – Flat wood or vinyl parts that are applied to the inside of the frame to extend it in width, which allows the frame to adapt to a thicker wall.
Exterior glazed – Glass installed from the exterior side of the window.
Fixed unit – A stationary window or door unit that does not open.
Flashing – A thin strip of metal or synthetic material that diverts water away from a window or skylight.
Frame – The enclosing box of a window or door that surrounds a sash or sealed unit, consisting of a head, sill and two jambs.
French door (Garden door) – A hinged door often available in one, two, three, or four-wide combinations with some fixed and some operating panels.
Garden door (French door) –A hinged door often available in one, two, three, or four-wide combinations with some fixed and some operating panels.
Glazing (1) – The generic term for the transparent, or sometimes translucent, material in a window or a door. It is most often glass.
Glazing/glazed (2) – The process of installing a sealed unit into a frame or sash using stops. Also refers to the type of glass used to make the sealed unit.
Glazing stop – Used to hold the glass into the frame.
Glider window (Slider) – An operating style of window that has a sash that slides horizontally to open.
Grille (Muntin bar) – Dividing bars or muntins used either on the surface or between panes of glass for a decorative appearance.
Half round window – True half round where the arch comes right down to the sill. The height is half the width.
Head – The top portion of a window or door frame.
Head and seat – Attached to the top and bottom of a bay or bow window as an option where the wall is not framed to follow the angle of the window.
Hopper window – A window unit in which the top of the sash swings inward.
Inside casing (Trim) – The moldings that surround the window and cover the frame on inside of the building.
Insulating glass unit (IG or IGU) -A combination of two or more panes of glass factory sealed using a spacer bar. Also known as a sealed unit.
Integral nailing fin – A pre-punched fin that is part of the extrusion, allowing for easy installation.
Interior glazed – Glass installed from the interior of the building.
Jamb – The side components of a window or door frame.
Jamb wrap – Applied on the jamb between the brickmould and weatherstrip of a door frame. It is usually painted metal.
Krypton gas – A rare atmospheric gas that is odorless, colorless, tasteless, nontoxic, monatomic and chemically inert. It is a better insulator than even argon gas.
Low-E glass – A type of glass consisting of a low emissivity coating on one side. A low emissivity coating significantly reduces heat loss in glazing combinations.
Mortise – A slot or rectangular cavity cut into a piece of wood to receive another part.
Mortise and tenon joint – Used at the corner of a wood sash to give strength and prevent sagging. Glued and machine squared for perfect fit in frame.
Mullion – An extrusion that joins windows. A sealant is applied between the units to prevent air and water leakage. A bullnose or profiled moulding is used on the inside and outside to cover this joint.
Multi-lock – One cam lock lever at the bottom operates multiple locking points to secure the sash to the frame.
Muntin bar (Grille) – Dividing bars or muntins used either on the surface or between panes of glass for a decorative appearance.
Nailing fin – A vinyl or metal flange attached to the perimeter of a window frame for insulation onto the rough opening header, jack studs and rough sill.
Operator – Refers to a door or a window that has an operable sash or panel that opens to allow passage or ventilation.
Patio door – A sliding door comprising of a panel fitted with an insulated sealed unit, with one operating panel sliding horizontally to provide passage. Sometimes available in three- and four-wide units.
Picture window – A type of window in which a sealed unit is glazed directly into window frame, without a sash.
Polyurethane core – Doors are foam injected for higher insulating value.
R-value – A term used to express the insulating values of a material or unit. A higher R-value indicates better insulating properties.
Reinforced steel – Comes in flat or tubular form that is completely enclosed in the vinyl frame for very large window combinations to structurally enhance the window.
Relative humidity – Humidity expressed as a percentage of the maximum possible humidity at a given temperature.
Rough opening – The opening built into a frame wall to receive a window or door unit.
Sash – A sub-frame component that surrounds a sealed unit. A sash can be either fixed (non-operating) or operating.
Sash balance – A coiled spring or spiral system integrated into the jamb liners to allow double hung or single hung sashes to open and close.
Sealed unit – A combination of two or more panes of glass factory sealed using a spacer bar. Also known as an insulating glass unit (IGU).
Shims – Rubber setting blocks used to position the glass into the window to ensure it is level, square and plumb.
Sidelite – A narrow fixed or operating unit joined to the side of a door frame combination.
Sill – The bottom component of a door or window frame.
Simulated dividing lites (SDL) – A decorative bar mounted on the exterior and interior of a sealed unit to provide the visual affect of dividing the glass into smaller units.
Single hung window – An operating style of window with a fixed top panel and a lower sash that slides up vertically.
Skylight – A window designed for roof installation, usually to provide natural light to interior building areas.
Slider window (Glider) – A type of window with one fixed sash and one or two units that slide sideways.
Solar heat gain coefficient – A measurement of how much solar energy a glass combination will allow to pass through. A higher coefficient allows more potential solar heat gain than a lower coefficient.
Solar transmittance – The percentage of total solar energy that glazing transmits through a window.
Sound transmission class – Rates the ability of glazing to block out sound from outside sources.
Spacer bar – The strip of material that maintains uniform separation between the layers of glass in the sealed unit of the window.
Stops – A window component that holds the sealed unit into a frame or sash.
Thermal break – A space or insulating material used to break highly conductive materials, to reduce heat transfer.
Transom – A window unit combined to the top of a window or door frame.
Triple pane (Triple glazed)- A sealed unit consisting of three panes of glass separated by two spacer bars.
U-value – A measurement of heat transmission.
Visible light transmittance – The percentage of visible light that is transmitted through a glazing combination. The type of sealed unit, coatings and tints will affect the percentage of visible light transmittance.
Weather stripping – A material used to create an air or water seal between operating components of a window or door.
Wind load – The amount of pressure exerted by the wind on a window or door generally expressed in pounds per square foot.
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Gem Windows & Doors
1590 The Queensway
Toronto, Ontario, M8Z 1V1 -
Phone: 1(888)806-2895
Fax: 416-503-9251