Air Space – The space between two panes of glass which make up an insulated glass.

Annealed – Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The breakage pattern of annealed glass is pointed, sharp-edged pieces and splinters.

Anodized – An electrochemical process that forms a protective coating of aluminum oxide on the surface of aluminum. The coating may be colored, and is integral to the metal and cannot be peel or flake.

Argon Gas – An inert, non-toxic gas placed between insulated glass panes in order to improve the insulating value.

Awning Widow – A venting style of window whose sash is hinged at the top, and when opened the sash cranks out and up.


Balance – A mechanical device, usually spring loaded, used in hung windows to counterbalance the weight of the sash when opening and closing. Common types are spiral and channel balances.


Casement Window – A venting window style whose sash is hinged on the jamb and when it is opened, the sash cranks out and to the right or left.

Clad – A material, usually aluminum, which is locked to the outside face of window and door products to provide a durable exterior surface.


Daylight Opening – The visible area of the glass that is seen and which is slightly smaller than actual full glass size.

Double Hung – A window style whose sash operate(s) vertically.


Egress Window – A window with a minimum clear opening size to allow occupants to escape through in case of fire or other emergency that renders normal exits impassable.


Fixed Window – A window that is not operable. Sometimes referred to as a “picture window.”


Glazing – Glazing is a term used for the process of mounting glass into windows and doors.

Glazing Bead – A moulding or stop that is placed around a window frame to hold the glass in place by pressure.


Hopper Window – A venting style window whose sash is hinged at the bottom and when it is opened, the sash cranks out and down.

Hung Window – Window whose sash operates vertically. Hung windows come in two styles; single hung has one operating sash. Double hung has two operating sash.


Insulated Glass – Two panes of glass enclosing a hermetically sealed air space. The glass panes (lites) are separated by a spacer to keep the sealed air space free of condensation.


Jamb – The vertical side of a window or door frame.

Laminated Glass – Two or more lites of glass (annealed or tempered) sandwiched with a clear or tinted polyvinyl butyl sheet. Common use includes safety glazing, burglar resistance, bullet resistance, sound transmission reduction, and sloped glazing.

Lite – A single glass pane or piece of glass.

Low-E (Low Emissivity) – A microscopically thin, almost invisible metal or metallic oxide layer(s) deposited on a window glazing surface and sealed in an insulated glass unit to reduce the U-factor by suppressing radiative heat flow through the window. Low-E glass keeps heat in during winter, and keeps heat out during summer, and helps to protect textiles from fading by blocking harmful U.V. rays.


Muntin (a.k.a Grids) – Individual pieces of a decorative grid installed on the exterior or interior of a window or sandwiched between the panes on thermal windows.  Help hold window panes in the sash and divide a window opening into smaller sections. They are used to enhance the aesthetics of a window or door.


Obscure Glass – Can also be referred to as frosted glass with a textured surface. Obscure glass is nearly opaque, letting light in but obscuring visibility through the glass.

Operating Unit – A window or door that opens. Also referred to as a vent.

Operator – Crank type hardware used to open a window which swings outward (casement), and keeps the window open at any position.


Rough Opening – Always expressed as width first, then height, it is the size of the opening needed to correctly accept a window or door.


Sash – The frame of the window that actually holds the glass in place, a sash consists of rails at the top and bottom with stiles at the side.

Sidelite – Glass, on either side or both of a door that lights the entryway or vestibule.

Sill – The horizontal base of a window or door main frame.

Single Glazed – One layer, or piece of glass, without an airspace.

Single Hung – In a double hung style window in which the top sash is fixed or inoperable.

Sliding Window – Window whose sash operates horizontally.

Solar Heat Gain Coefficient (SHGC) – Measures the proportion of solar energy penetrating a building. SHGC is expressed as a value between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits.

Spacer – A material placed between 2 or more panes of glass in an insulated glass unit (IGU) to bond and seal the glazing unit.

Stile – A vertical sash member.

Stop – Moulding used to hold, position and/or separate window parts.

Sweep – Rubber or vinyl strip applied to the bottom of a door to create an effective seal against sill and threshold.


Tempered Glass – Tempered glass is produced by subjecting annealed glass to a precisely controlled heating and fast-cooling process to increase its strength. Tempered glass when broken, breaks into small fragments that greatly reduce the chance of injury. It is required by building code in some instances (door lites, shower doors, etc.) and is the type of glass used in automobiles.

Tinted Glass – A colorant is added to clear glass to give it a tint. The tinting increases protection form sun exposure and enhances thermal efficiency. Common shades are bronze and gray, with gray being slightly more thermally efficient.

Threshold – Made of wood or aluminum, and beveled or tapered on each side, used with exterior or interior door frames.

Transom – A framed area immediately above a door or window, containing glass.

Triple Glazed – An insulated glass unit consisting of three panes of glass with two internal air spaces.


U-Value – A measure of the rate of non-solar heat flow through a material. It is the opposite of R-Value. Lower is better when comparing U-Values.

Weep Hole – An opening cut into a window sill or sash rail to allow water to drain to the exterior.

Window Size – The actual size of the window or door. Always expressed in width first, then height.