Glossary of terms for windows and doors
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Air Chambers

Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.

Air & Water Infiltration

The amount of air and water that passes between a window sash and frame. In windows it is measured in terms of cubic feet of air per minute, per square foot of area. The lower the number, the less air the window lets pass through.

Argon Gas

An odorless, colorless, tasteless, non-toxic gas, six times denser than air. It is used to replace air between the glass panes to reduce thermal transfer.

Astragal

The center member of a double door, which is attached to the fixed or inactive door panel.

Awning Window

A top-hinged window that can be cranked open from the bottom, swinging outward for ventilation.

Balance System

Device for holding a vertically sliding sash in any desired position as a means of counterbalancing the weight of the sash during opening and closing.

Bay Window

A combination of three windows that project out from the wall of the home, joined at 30 or 45 degree angles.

Bow Window

A combination of four or more windows that project out from the home, joined at a 10-degree angle.

Brick Mould

An exterior (milled) trim piece to cover the gap between the window / door frame and masonry in a masonry (or other) opening. In addition to serving as an anchor point for installation of the unit, brick mould provides a boundary for brick or other siding material on the face of the building and attachment of hardware (sometimes called Shake mould).

Bronze-Tint Glass

Glass tinted with a light bronze colouring used to reduce the amount of light transmitted through the pane.

Butyl

A rubber material that seals the glass to the spacer, creating an airtight and water-tight IG unit. Butyl has the lowest gas permeability of all rubbers.

Cam Lock and Keeper

The mechanism that pulls the sash together when placed in the locked position.

Caming

Grooved, usually H-shaped, rod of cast lead used, as in stained glass, to hold the panes or pieces of glass together.

Capping

Cosmetic covering, usually found on the exterior of the window or door to achieve aesthetic sight lines or to integrate the window or door system into the building surface or weatherproofing system. Also called cladding.

Casement Window

A window hinged along either vertical edge which opens out from the side opposite to the side that is hinged, providing ventilation as required.

Caulk

To seal cracks and joints around window and door frames to prevent air and air infiltration.

Caulking

A mastic compound for filling joints and sealing cracks to prevent air and water infiltration, commonly made of silicone, bituminous, acrylic, or rubber-based material.

Center of Glass U- and R-values

The U- and R-values measured from the center of the glass to 2-1/2" from the frame.

Cladding

Any material locked to the outside faces of doors and windows (exterior skin) to provide a durable, low-maintenance exterior surface.

Condensation

Excess humidity manifesting itself in the form of a thin film of water on a cold surface.

Conduction

Transmission of energy (heat and cold) through a solid material by direct contact.

Convection

Heat transfer by currents that flow from a warm surface to a colder one.

Dead-air space

The space between the panes of glass of a sealed unit.

Desiccant

A drying agent (similar to silica gel) used in insulating glass to absorb water vapour in order to prevent fogging.

Divided Lite

A window with a number of smaller panes of glass separated and held in place by muntins.

Door Jamb

The part of a door frame which surrounds and contacts the edges of the stiles and top rail of a door; jambs may be classified as (1) "head or "side" jambs and (2) "plain" or "rabbeted".

Door Slab

A door without lites or sweep installed.

Dormer

A space which protrudes from the roof of a house, usually including one or more windows.

Double Glazed Units

Units consisting of two lites of glass and one air space in between.

Double Glazing

In general, two glasses separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In factory-made double glazing units, the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties.

Double Hung Window

A window that has two operable sashes which slide vertically.

Dry glazing

An alternative method of placing glass in a door or window. No glazing mastic is used. Dry glazing is recommended whenever reflective coatings are glazed to the first surface.

Dual-durometer

A material that has two or more levels of flexibility. An example is the weather stripping used between the frame and sash of a casement window.

Egress

Literally, an exit (a means of exit). Actual opening size determined by local building codes.

Egress Code

The code that requires a minimum opening of a window for persons to exit or for firefighters to enter.

Egress Window

A window with minimum clear opening size as required by the local building code, to allow occupants to escape through the window in case of a fire.

Emissivity

To emit is to give out, to discharge.

In the case of glass, essentially, to reradiate absorbed energy (heat). Emittance is the ratio of the total radiant energy emitted by a given surface to that emitted by an ideal black body at the same temperature.

ENERGY STAR®

ENERGY STAR® is an independent U.S. government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR® guidelines have helped double the efficiency of the windows they endorse.

Entrance Door

A door on the front entrance of a structure; also known as a "front" or "main" entrance door; may be single or in pairs.

Exact Window Size

The dimensions of a window or door unit measured along the outside of the frame.

Exterior Stop

The removable glazing bead that holds the glass or panel in place when it is on the exterior side of the light or panel, in contrast to an interior stop located on the interior side of the glass.

Extrude

The process of shaping aluminum or vinyl by forcing it through a die to produce continuous strips of material formed to a specific shape or profile. The material is forced through a die which has been cut to match the desired profile. As the material is extruded through the die, it is cut to the desired length and allowed to cool. This process is very common in creating frame and sash materials, as well as glass insulating spacers and glazing sealers.

Failed IG Unit

An insulated glass unit failure exhibits permanent material obstruction of vision through the unit due to the accumulation of dust, moisture or film on the internal surface of the glass. Surface numbers two and three in double-glazed units are the affected surfaces.

Fenestration

An architectural term referring to the arrangement of windows in a wall. From the Latin word, "fenestra," meaning window.

Fire Rated Doors

A door which has been constructed in such a manner that when installed in an assembly and tested will pass ASTM E-152 "Fire Test Of Door Assemblies," and can be rated as resisting fire for 20 minutes, 30 minutes, 45 minutes (C), 1 hour (B), or 1-1/2 hours (B). The door must be tested and carry an identifying label from a qualified testing and inspection agency.

Fixed Panel

An inoperable panel of a sliding glass door or slider window.

Flanker

The designation given to units that flank a center picture unit in a double or triple combination window.

Flashing

Sheet material that protects and bridges the joint between the window or door frame members and the adjacent construction for the purpose of preventing water penetration by draining water away from the window or door to the exterior.

Flat Glass

All types of glass (rolled, float, plate, etc.) produced in a flat form, regardless of the method of production.

Float Glass

Glass formed by a process of floating the material on a bed of molten metal. It produces a high-optical-quality glass with parallel surfaces, without polishing and grinding.

Frame

The enclosure in which the window sash or door panels are mounted.

Full Screen

A screen which covers the entire opening of a window.

Fusion-welded

The process of heating mitered corners to 2008ºF and bringing the heated corners into contact until they fuse together into a single piece of vinyl.

Gas Filled Units

Insulating glass units with a gas other than air (usually an inert gas such as argon) in the airspace between the panes. This is done to decrease the unit's thermal conductivity (U-value) and increase the unit's sound insulating value.

Gasket

A pliable, flexible continuous strip of material used to affect a watertight seal between the sash and the frame of roof windows much like the seal around a refrigerator door.

Geometric

Specially designed windows classified as either straight line geometries such as rectangles, triangles, trapezoid, octagons, pentagons, etc., or radius geometries which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc.

Glass

An inorganic transparent material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate) with small quantities of alumina, boric or magnesia oxides. Available in clear, bronze, grey and obscure.

Glazing

The process of sealing the glass to the sash.

Glazing Stop

The part of the sash or door panel which holds the glass in place.

Grills

Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass

Half Screen

A screen which does not cover the entire opening of a window. Used on the bottom half of single hung units and on the operating sash of single sliders.

Head

The horizontal top portion of a window or door frame.

Head expander

An individual U-channel installation accessory that may be fitted to the head of a replacement window to accommodate differences between rough opening and window heights.

Header

A horizontal framing member placed over the rough opening of a window to prevent the weight of the wall or roof from resting on the window frame.

Hinge

A movable joint enabling a window or door to swing open.

Hinge Mortise

The area cut away to accept the hinge leaf for mounting on the door frame or door edge.

Horizontal Slider

A window with movable panes that slide horizontally.

I.G. Unit (Insulating Glass Unit)

Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.

Infiltration

Leakage of air and water into or outside the house, through cracks around the sash or the window frame.

Interlock

A design feature which enables sashes to engage one another when closed.

Internal Grills

Grids mounted between the two panes of glass of an insulated glass unit.

Jamb Extensions

Flat parts made of vinyl, wood or other materials which are attached to the inside edges of a window jamb to extend it in width to adapt to a thicker wall.

Jamb

Vertical sections of the door and window frame.

Keeper

The part of a window lock, mounted on an opposing surface of the window, that the lock arm locks under or into to pull the sash into a locked position and fully releases it when opened.

J-channel

Integral extension on the outside of a new construction window that eases installation on siding applications.

Jamb

Vertical sections of the door and window frame.

Keeper

The part of a window lock, mounted on an opposing surface of the window, that the lock arm locks under or into to pull the sash into a locked position and fully releases it when opened.

Knocked Down

Not assembled; parts for a window (or door) frame pre-manufactured for assembly at a later date on the job-site.

Krypton Gas

An inert, odorless, colorless, tasteless, non-toxic gas which is about 12 times more dense than air. It is used to replace air between the glass panes to reduce temperature transfer and deter convection. Used when a higher performance is desired than that produced with argon gas.

Laminated Glass

Two or more pieces of glass bonded together over a plastic interlayer.

Lift Handle

A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.

Lift Rail

A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.

Lite

A unit of glass in a window or door.

Lineal Footage

A dimension expressing length (in feet) only. For example, the width of a unit (in inches) plus the height (in inches) x 2 divided by 12 = the perimeter measurement of the unit in lineal feet.

Lintel

A horizontal member above a window or door opening that supports the structure above.

Low E (Emissivity) Glass

Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.

Main Frame

The head, sill and jamb sections of a window.

Masonry Opening

The space in a masonry wall left open for windows or doors.

Mechanically Fastened Frame

Refers to window and door frames fastened with screws.

Meeting Rail

The horizontal sections of a pair of sashes that meet when the sashes are closed.

Mesh

Fabric made of fiberglass used in the making of screens.

Mullion

A vertical or horizontal connecting unit between two or more windows.

Multi-Point Locking

A term used for locking hardware that engages a window sash to the frame at multiple locations with a single throw of an operator.

Muntin

Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lites. Also called a windowpane divider or a grill.

Nailing Fin

An extrusion attached to the main frame of a window used to secure the unit to the rough opening.

Night Latch

A hardware which, when extended, restricts the sash opening to a predetermined dimension.

Obscure Glass

Glass that has been made translucent instead of transparent.

Operable window

A window that can be operated for ventilation.

Operating Panel

In a two panel window or door the panel that swings or slides open.

Operator

Crank-operated device for opening and closing casement windows.

Pane

One of the compartments of a door or window consisting of a single sheet of glass in a frame. Also, a sheet of glass.

Panel

A major component of a sliding glass door, consisting of a lite of glass in a frame installed within the main (or outer) frame of the door. A panel may be sliding or fixed.

Patio door

A glass door that slides open and close on adjustable tandem rollers. Available in 2, 3 and 4 section configurations.

Picture Window

A window that does not open (no moveable sash).

Pivot Bar

A metal post attached to a moving sash and seated in a balance shoe that allows the window sash to tilt.

Pull Handle

A handhold for sliding the sash back and forth. Handle implies that the handhold is not continuous across the sash.

Pull rail

A handhold for sliding the sash back and forth. Rail implies that the handhold is continuous across the sash.

PVC

An extruded or molded plastic material used for window framing.

Quarter Round Window

Stationary or operating window shaped as a quarter circle.

R-value

The resistance that a material has to heat flow. The higher the R-value, the greater the resistance. The heat loss by windows is expressed with U-values, or U-factors. U-values are the mathematical inverse of R-values. So an R-value of 2 equals a U-value of 1/2, or 0.5. Unlike R-values, lower U-value indicates higher insulating value.

Radiation

Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.

Relative Humidity Condensation Point

The relative humidity level at which visible water vapour or other liquid vapour begins to form on a cold surface. If the temperature changes but no water vapour is added or taken away, then the relative humidity will also change and will increase as the temperature falls. The relative humidity will continue to rise with falling temperature until the dew-point is reached that is, the temperature at which the relative humidity becomes 100 percent.

Replacement Window

A window that is designed for and subsequently installed after the removal of all or part of a previously-installed window.

Retrofit

Adding or replacing items not provided at the time of original construction. Typical retrofit products are replacement doors and windows, insulation, storm windows, caulking, weather-stripping, vents, and landscaping.

Reveal

That part of the edge of a door or window jamb not covered by the casing.

Rollformed Screen Frame

A method of fabrication in which material (vinyl) is placed on a machine where the material is formed into shape using differently shaped rollers and pressure.

Rough Opening

The framed opening in a wall into which a window or door unit is to be installed.

Safety Glass

A strengthened or reinforced glass that is less subject to breakage or splintering.

Sand Blasting

Compressed air forces an abrasive material (resembling sand) through a nozzle onto the surface of the glass. This process removes the surface of the glass, which gives the sandblasted area a frosted look.

Sash

The part of the window which contains the glass.

Sash Lift

A handle for raising the lower sash.

Sash Stop

A molding that covers the joint between window sash and the jamb.

Screen

Woven mesh of metal, plastic, or fiberglass stretched over a window opening to permit air to pass through, but not insects.

Sealant

A compressible plastic material used to seal any opening or junction of two parts, such as between the glass and its sash, commonly made of silicone, butyl tape or polysulfide.

Shims

Wood wedges (often wood shingles) used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation.

Side Lite

A tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule.

Sill

The horizontal, bottom section of window and door frame.

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 lite.

Single Hung

A window in which one sash slides vertically and the other sash is fixed. Generally, the bottom sash is the operable one.

Sloped sill

The sill of the window that has a downward slope to the outside, to assist in excessive rainwater runoff.

Solar Heat Gain

The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.

Spacer

A strip of material placed between two pieces of glass in order to maintain a uniform width between the two pieces and prevent sealant distortion.

Square Foot

A unit of measure for designating an area of one foot by one foot. Derived from width (in inches) x height (in inches) divided by 144 = area in square feet.

Stain

Attack on the glass surface by water or other solutions.

Stile

The vertical edges of a door window or screen.

Stop

A trim member attached to the window frame to stop the sash of a projecting window when closed to prevent it from swinging through the opening. It also covers the perimeter crack between the sash and the window frame in double hung and sliding windows and prevents the sash from coming out of the frame. Stops used at the top or bottom of the balance channel prevent the sash in hung windows from hitting when opened.

Stud

Vertical wood framing members that form a frame wall. In normal construction these are eight foot-long 2" x 4"s.

Tape Glazing

Two-sided tape used to secure and seal the glass to the sash. Also known as wet glazing.

Tempered Glass

Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. Should the glass break, it falls out of the frame and is shattered into small pebble like harmless pieces without sharp edges. This is by design and is proof of a well tempered product, not of a defective product.

Thermal Break

The addition of a thermal insulating material between two thermally conductive materials.

Thermal Expansion

A change in dimension of a material as a result of a temperature change.

Tilt Latch

A mechanism that unlocks the sash and allows it to tilt in for cleaning.

Tilt-in sash

A sash that can be tilted to the interior for cleaning.

Tinted Glass

Glass with a material added to give the glass a light and/or heat reducing capability and color.

Total Unit U- and R-values

The heat loss by windows is expressed with U-values, or U-factors. U-values are the mathematical inverse of R-values. So an R-value of 2 equals a U-value of 1/2, or 0.5. Unlike R-values, lower U-value indicates higher insulating value.

Transom

A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.

Transom Window

A large fixed window semi-circular or an artistic variation of that shape mounted above a door or a group of windows primarily for additional light and aesthetic value.

True Divided Lite

A term commonly used to describe the arrangement of grills in a single sealed unit giving the effect of divided lites (individual panes of glass in a single unit).

U-value

Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality.

Ultra Violet

Type of radiation with wavelengths shorter than those of visible light and longer than those of X-rays. Causes sunburn, fading and breakdown of fabric, wood, furniture and other exposed surfaces.

Vent

The operating portion of a window that swings or projects in or out.

Venting Unit

A window or door unit that opens or operates.

Vinyl

Vinyl is a generic term for modified PVC (Polyvinyl Chloride).

Vinyl Window

A window whose frame and sashes are made from vinyl.

Vinyl Clad

A door or frame made of wood with an exterior skin of vinyl.

Warm Edge Spacer

Use of a non-conductive edge spacer in insulating glass units instead of the conventional aluminum (conductive) edge spacer. "Warm Edge" spacers may be made of butyl, silicone foam or other non-metallic materials and sealants.

Weatherstripping

Material used to form a weather-resistant seal around operable sash to prevent air and water infiltration.

Weep flaps

A weep hole that is covered with a vinyl flap that allows water to escape, while keeping insects out.

Weep Holes

Small openings in the window or door sill designed to allow water to escape.

Weep Slots

Slots or holes in the sill (bottom) member of the window and door frame that provides an outdoor release of infiltrated rainwater.

Wet Glazing

A silicone-based substance used to secure and seal the glass to the sash.

Window

A glazed opening in an external wall of a building; an entire unit consisting of a frame sash and glazing, and any operable elements.

Window Frame

The fixed frame of a window which holds the sash as well as the operating hardware for the window.

Window Hardware

Various devices and mechanisms for the window including cords, chains, fasteners and locks, hinges and pivots, lifts and pulls, pulleys, sash weights, sash balances etc.

Window Size

Size of the actual window frame always expressed as width first then height.

Window Style

The description of the way a window operates; example hung, sliders, casements etc.