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Window Glossary

Learn what each part of the window is called.


Metallic element of the earth's crust that is silver and white with a hint of blue tones. Not easily tarnished or corroded. Has very good thermal and electric conductivity and makes strong, durable windows.

Aluminum Cladding

Provides a protective shell for exterior surface of windows. It does not scratch, crack, flake, or blister easily.

Annealed Glass

Is standard float glass before it is treated for tempering or heat strengthening.

Arch-Top Window

Also known as a radius window, this window has a curved top. Similar windows would be full round, half-round, quarter-round, or arch top products. These windows may be available in operating or none-operating configurations.


Gas is injected into the airspace of a glass unit for insulation value.


Astragal is the vertical trim that is attached to one of the sashes of a French door. Astragal is used to bridge the gap between the sash/panels when closed.

Awning Window

A window that has a sash that is hinged at the top but opens from the bottom.

Constant Force Balance System

Interlocking spring system that helps you move the window up and down.


Mechanical device used in single- and double-hung windows to counterbalance the weight of the sash during opening and closing. Ball Bearing Hinge Most commonly used to reduce friction of the hinge flange, for doors that receive high traffic.

Basement Window

Used to provide ventilation for basements or similar spaces. Basement windows are sash units that swing from the top or bottom. Most commonly known as a "Hopper Window".

Bay Window

A set of three windows projecting out of a building at 30, 45 or 90 degree angles. The center window is parallel with the structure.

Bow Window

Four or more window units that adjoin together and project 10"-20" from a building wall forming a radius.


Exterior casing for doors and windows that are used as a boundary between the frame and the siding.

Bulb Seal Weather Strip

Weather seal that has a rounded and closed profile.

Cable Support Kit

Typically used in a bay or bow window, this set of hardware is designed to tie a window to the structure. It prevents window sagging and supports the projected portion of the window.

Cam Lock

Forms a tight weather seal, this single-point locking mechanism uses a "cam" action to lock and pull the window sash against the frame.

Cam Pivot

Allows the sash to "pivot" for removal, this is a pin on the bottom corners of single and double-hung sashes.


Pieces of metal that hold individual pieces of glass together to create decorative glass. Types of metals are lead, brass, zinc or nickel.


A thin metal or vinyl covering that is fitted over building components for weather protection and finished appearance.


Exposed decorative moulding or profile around a window to cover the space between the window frame and the wall. Casement window Hinged on either the right or the left side allowing the sash to open outward in a swinging motion.


Compound used for sealing cracks and filling joints, this prevents any possible leakage of air or water.

Cellular PVC

Extruded polyvinyl chloride material used in window and door components and trim.

Cellulosic composite

Generally, a material combining an organic material, such as wood fiber, extruded with plastic.


An office of the National Research Council that evaluates building materials.


Canada's housing agency, mortgage insurance, housing data, housing research

CSA International

A standard writing and certification association.

Condensation Resistance Factor (CRF)

A rating of window's ability to resist condensation. The higher the CRF, the less likely condensation is to occur.


A term used for window or door components that consist of two or more materials, such as glass fibers or wood and plastic.

Meeting Rail

In a double-hung window, this is the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted.

Circle-Top Window

A type of window featuring curved components such as full round, half-round, quarter-round, arch top and spring-line products. Circle top windows may be available in either operating or fixed configurations.


When excess humidity in warm air is released as water droplets onto a cold surface such as a pane of glass.

Cottage Window

Either a double or single-hung window that has a smaller top and larger bottom sashes.

Crank Handle

A handle that has a knob and arm assembly to open casement or awning window.

Design Pressure Ratings

A way to specify the performance of windows based on structural, air, and water ratings. The ratings measure a product's ability to withstand forces in both negative and positive directions, while the window or door is closed or locked.


A dying agent that is used in manufacturing insulated glass to prevent fogging of the insulated unit.

Diamond Lite

This is a decorative diamond grille pattern.

Divide Lite

A clear opening in a window that is divided into small sections using a grid system on the exterior and interior. Note: This is never in-between the glass.

Door Frame

Used to fasten the door system to the structure with structural members (head, jambs, sill).

Door Jamb

The two vertical frame members as well as the upper horizontal that house the door panel, classified as side or head jambs.

Double Glazing

Two panes of glass separated by a spacer to form a air pocket for insulation.

Double-Hung Window

A window that has both an upper and lower sash that slides vertically.

Double-Strength Glass

Refers to the thickness of the glass. Thickness starts at 3/32" to 1", standard size would be 1/8".

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.

Dual-Durometer Weather Stripping

Designed with two different materials providing above average performance.

Dual Seal

Used in sealing dual-pane windows where the primary seal is polyisobutylene and the secondary seal is silicone.

Egress Opening

The space between the top of the sill of the frame of an open window and the bottom part of the raised sash, multiplied by the space between the jambs of the opening.

Energy Star

An independent U.S. government program established designation to recognize energy efficient products based on a set of guidelines.

Extension Jambs

Wood or other material that is fastened to the inside edges of a window to increase width that allows adaptation to a thicker wall.

Extruded Nailing Fin

Metal or plastic flange that is attached on the perimeter of a window unit mostly used for New Construction projects.


Formed when material is forced through a die.

Eyebrow Top

A door with a top that slopes down from the center and up on either end.


The person or business that assembles all the component parts into a completed door, window, or sash unit.

Factory Mulled

Two or more window units that have been attached together at a manufacturing plant.


The arrangement and design of doors and windows on the exterior of a building.


A door or window that is inoperable or non-venting.

Fixed Sash

A window sash or door panel, often used in combination with other types of window and sash units, that is fixed to the frame and intended primarily for viewing purposes and for admitting light.

Flanker Unit

An outside door or window that is inoperable or non-venting.


Sheet metal that is overlapped to provide protection against water leakage.

Float Glass

A quality of glass that is made by taking a ribbon of molten glass and feeding it across a bath of heated liquid such as molten tin.


A deposit of film left on the interior surface of an insulated sealed glass unit. Fogging occurs when extreme conditions are present or when seals fail.

Folding Crank Handle

A type of hardware that is used to operate casement windows. The handle has the ability to easily fold away when not in use.


The assembly of structural members such as the sill, head or jam that is used to fasten a door panel or window sash to a building or structure.

French Door

A style of door where two panels open completely making a space equal to approximately twice the width of the panel.

Full Round

A type of geometric shape and radius that is available specifically for vinyl, wood and aluminum windows.

Full Screen

A screen that fills the entire window opening of a double-hung window from top to bottom.

Fusion Welding

When vinyl windows, door frames, or sashes are joined together. Each piece is heated and bonded together to reduce water and air infiltration.

Gable Top

A five sided geometric shape available in a vinyl, wood and aluminum picture window frame bar.

Garden Window

Popular in greenhouses and kitchens for plants, a garden window projects out from the side of the building. The slanted glass roof allows heat and light to enter.

Grids Between The Glass (GBG)

A decorative divided lite option for patio doors or windows. These grilles are placed between the panes of insulating glass and are maintenance-free.

Geometric Window

Specialty geometric shaped windows, available in triangle, rectangle, octagons, trapezoids, half-rounds, pentagons, quarter-rounds, sectors, full rounds, and ellipse shapes.

Glass Stop
Trim that covers the edge of the glass.

Glazing is used as a process to mount glass into doors and windows. The purpose of glazing is to retain the glass adequately under the design load, provide an effective weather seal, prevent loads or pressure points on the glass resulting from building movement, prevent glass-to-metal contact, and minimize glass breakage from mechanical or thermal stress. Glazing also refers to the lowest quality of plate glass.


A decorative removable or non-removable grid on the exterior or interior of the glass, between the glass panes, or in any combination of these locations that divides a window opening into smaller openings to create simulated divided lite or true divided lite.

Grills Between The Glass

Placed between the panes of insulating glass, grilles are divided lite options for patio doors or windows. They are also maintenance-free.


A screen that only covers one sash and fills half of the opening of a double-hung, single-hung or sliding window.


A half-round window is a half of a circle.

Handle Set

Hardware that attaches to the face of a sliding door that allows the door to open and close.


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 Transfer of heat from outside to inside by means of convection, conduction, and radiation.

Heat Loss

Heat loss is the transfer of heat from inside to outside by means of convection, conduction, and radiation.

Hopper Window

A sash unit that typically swings from the top or bottom is used to provide ventilation to basements.

Horizontal Gliding Window

Two or more sashes that slide horizontally past each other; one or more of the sashes may be fixed or inoperative or all the sashes may operate. In a closed position, the sashes come together to form a vertical meeting rail.

Insulated Glass

Two panes of glass with material between the two panes making it difficult for heat or cold to pass through.


Doors that swing to the interior of a home.

Insulating Glass Unit

Two or more panes of glass separated by a spacer.


Provides hooking action on a window or door between the sash rail and the sill or jam. Interlocking provides security and reduces air infiltration.


Perimeter flange on the outside of a window that allows siding on a home to slip between the nailing fin and the trim.


Several small horizontal glass slats held together by a metal end frame and then attached to the face of a window frame, side jams, door rails or stiles.


The vertical frame components of a door or window assembly.

Jamb Adjuster

Used to ensure that a product is installed squarely, these are adjustable screws designed for mounting door and window frames into rough openings.

Jamb Extension

Extends the depth of a door or window frame and usually has a larger depth than a jamb liner.


A bracket used as a latching point.

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. Lift Rail A rail on a single or double hung window designed with an integrated method of lifting the operating sash.


A framed opening in the glass within a door panel or sash used in reference to glass divided by a grid into multiple smaller openings.

Lock Rail

The intermediate rail of a door at lock height.

Low-E Glass

A type of insulating glass that blocks harmful ultraviolent rays as well as the sun's infrared heat so homes stay cooler in the summer.

Mulled Unit

Two or more window units joined together.

Multi Point Lock

A locking system with more than one lock.


The individual pieces of a decorative grid that work to divide a window opening into smaller sections.

Nailing Fin

A plastic or metal flange that is inserted into a point on the head, jambs and sill of window units. Nailing fins are commonly used to secure windows or doors to an opening in new construction installations.

National Fenestration Rating Council (Nfrc)

An independent third party certification organization with accepted standards for evaluating and certifying energy performance.

New Construction Window

A window installed during the original construction of a building.

Obscure Glass

A type of decorative textured glass that partially or fully obscures the view. Obscure glass allows for privacy while allowing light to enter a home.

Operating Sash
Operating (moving) portion of a window.

Hardware (excluding hinges) used to open and close windows.

Oriel Window

Either a double or single-hung window that has a smaller bottom and a larger top sashes.

Out-Swing Door

Refers to a door that swings outward rather than inward on a home.


A large arch top window that is flanked by smaller windows on either side.


Refers to one piece of glass.

Patio Door

A door made of mostly glass that opens onto a patio, deck, or backyard of a home.

Picture Window

A fixed large window with smaller adjacent windows.

Pile Weather stripping

A type of weather stripping that has a pile, also known as fuzz, that helps reduce dust around a window sash or door panel.

Prairie Grills

A type of divided lite grille pattern that borders the glass on the outside of the sash or frame, sometimes referred to as Queen Anne grilles.


Polyvinyl Chloride (PVC) is an extruded or molded plastic material framing as well as a thermal barrier.

Quarter Round

A radius and geometric shape used for vinyl and aluminum windows.


The amount of resistance a window has to heat flow or thermal transfer. The higher R-Value, the better the insulation.

Radius Window

A window available in operating or fixed configurations with curved components that may include full round, half-round, quarter-round, arch top and springline products.

Reinforcement Bar

Reinforcement bars have a steel or aluminum profile and is used to reinforce patio doors and vinyl windows.

Replacement Window

Any window custom made to replace an older window which does not have a perimeter nailing flange.

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). Most commonly this opening is ½" inch bigger than the window being installed.

Round Top

A 180-degree top curve feature on a window or door, also known as a true radius top.


Stiles and rails that are welded together to form a frame for holding glass in a window.

Sash Cord

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

Sash Weights

Concealed cast-iron weights used to counterbalance the sash of older double-hung windows. Seal Failure When the seal around the perimeter if insulated glass unit is lost which results in fogging between panes.

Shading Coefficient

The measure of a window's ability to transmit solar heat relative to the ability for a 1/8" clear glass pane. The higher a unit's SC, the more heat it transmits, and the less shading ability it has.

Solar Heat Gain Coefficient (Shgc) Rating

A measurement of the amount of solar radiation present throughout a piece of glass or door material. The lower the SHGC, the fewer UV rays that cause heat gain will come through the window.


Narrow fixed units mulled or joined to operating door units to give a more open appearance. Sill: The main horizontal member that forms the bottom of the frame of a door or window.

Sill Expander

An extrusion that is attached to the bottom of the window to adapt for and angle in the rough opening of the window.

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 pane 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 top sash that does not move. Sliding patio Door A door with one or more panels that slide horizontally past each other, very commonly used in areas with minimal space.

Sliding Window

Includes one stationary sash and another sash that moves to the left or right in groves or tracks.

Soft Coat Lowe Glass

A thin layer of materials offering low emissivity or solar control benefits are applied to glass in a manufacturing center.

Solar Heat Gain Coefficient (Shgc)

A measurement of how much solar radiation is present through a piece of glass or door material. The lower the SHGC, the fewer UV rays that cause heat gain come through the glass.



A component that is typically metal that separates panes of glass to create airspace.

Sputter Coating

A thin layer of materials offering low emissivity or solar control benefits are applied to glass in a manufacturing center.

Stationary Sash Or Panel

A door panel or window sash that is typically used in combination with other types of window and/or sash units, fixed to the frame, and is used primarily for viewing and admitting light.

Storm Door Or Window

A door or window that is meant to cover, protect, and insulate an exterior door or window. Typically contains glass and screening material.


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. Stress Crack Resulting from a stress condition on the edge of glass, a stress crack is a defect in an insulated glass unit.


A polymer foam, no metal WarmEdge spacing system.

Tempered Glass

Extra strength heat-treated glass that withstands abnormal pressure and force on the surface, will not break into sharp pieces.

Three-Lite Slider

A vinyl horizontal slider where the center lite is generally equal to the width of both vents together.

Thermal Break

A low conductivity element that is placed between higher conductivity elements to reduce the flow of heat or cold, often used in aluminum windows.

Tilt Latch

A latch at the end of a window checkrail allowing the sash to easily release from the jamb liners and tilt into the structure.

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 Often a rectangular window placed over a door or another window.


A four sided geometric shape available specifically for an aluminum or vinyl picture window frame bars.

Tilt Window

A double-hung window where the sashes tilt inward to allow for easy cleaning of the exterior glass.

Tinted Glass

Colored glass that protects a home from harsh direct sunlight.


A three-sided geometric shape used for an aluminum or vinyl picture window frame bar.

Triple Pane

Three panes of glass in one insulated glass unit, offering optimal thermal performance.

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.

True Radius Top

A 180-degree top curved feature on a door or window.

Twin-Vent Slider

A vinyl horizontal slider where the center lite is generally equal to the width of both vents together.


A number representing the rate of heat loss through a door or window; the lower the number, the greater a window can handle the transfer of heat.

Ultraviolet (UV)

The type of rays that exist outside the visible spectrum. Too much exposure can cause plastic metals to change shape and dark paint finishes to chalk or fade.


A specialized process where a decorative pattern is grooved into glass, V-Groove is available in standard as well as grid patterns and can be created in various polishes and shadows.


A thin layer of wood that is typically rotary-cut, sliced or sawn from a log, bolt or flitch.


The operating sash in a window


Either rigid or flexible, this polyvinyl chloride material is used in glazing channels and weathering of doors and windows.

Virgin Extrusion

The original vinyl extrusions that do not have any regrind added.

Visible Transmittance

How much light actually comes through a product expressed as a percentage. The higher the VT, the more light transmitted.

Warm-Edge Technology

A way to create insulated glass using a non-thermal conductive spacer bar.


Metal, plastic, or vinyl fiber strips that fit tightly against the window or door frame to prevent air infiltration.

Weep Hole

Used to drain water out of a window or patio door, a weep hole is visible exit or entry point of a drainage system.

Wind Load

Wind Load


An opening in a building designed to let in air and light with the ability to block outside elements and can be opened and shut. Windows are created using a frame and sash containing a transparent material such as glass.

Window & Door Manufacturer's Association

Window & Door Manufacturer's Association

Window Unit
Some combination of the frame, sash, weather stripping, sash opening mechanism, screens and storm sash assembled as a complete operating unit.
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