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Glossary, Windows and Doors Installation in Toronto


Air and Water Infiltration

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

Air Chambers

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

Argon Gas

An odourless, colourless, tasteless, non-toxic gas; six times denser than air. Used to replace air between glass panes, reducing thermal transfer.


The central member of a double door, attached to a fixed or inactive door panel.

Awning Window

A top-hinged window you crank to open. They’re often installed above or below other windows, or above doors for increased ventilation and lighting.


Balance System

A device that holds a vertically sliding sash in any desired position. Its main functionality is counterbalancing the weight of the sash during opening and closing.

Bay Window

Large windows that come in angled sections; the middle pane is fixed, while some models feature outer panes that open up for airflow. Bay windows are often found in living areas; they are inviting, create depth, and can significantly increase the amount of light that a room receives. These windows are large and often feature inner ledges that can be decorated.

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 that covers the gap between a window or door frame and the opening that it sits in. In addition to serving as an anchor point for installation of the unit, brick moulds provide 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, which reduces the amount of light allowed through the pane.


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


Cam Lock and Keeper

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


A grooved, usually H-shaped, rod of cast lead used to hold window panes or pieces of glass together.


Cosmetic covering, usually found on the exterior of a window or door for aesthetics, or to integrate the window or door system into a building surface or weatherproofing system. Also known as ‘cladding’. Usually made of aluminum.

Casement Window

These windows open outward via a hinge mechanism. They can open on the left or right side, and are perfect for spaces that need adequate ventilation. Casement windows are energy-efficient and are effective at minimizing noise. They are often installed in hard to reach spaces, given the ease of which they can be opened by the crank handle.


Sealing cracks and joints around window and door frames to prevent air and water infiltration.


A mastic compound used to fill joints and sealing cracks to prevent air and water infiltration; commonly made from silicone, bituminous, acrylic, or rubber-based material.

Centre of Glass - U-values and R-values

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


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


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


Sealing cracks and joints around window and door frames to prevent air and water infiltration.


Dead-Air Apace

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


The locking mechanism installed on entry doors. It features a throw (the bolt) that locks into place within the frame. Deadbolts provide greater security than standard door locks, as they are very difficult to open through forced entry.


A drying agent (similar to silica gel) used in insulating glass to absorb water vapor. Prevents fogging.

Divided Lite

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

Door Jamb

A door jamb is an essential component of a door frame, providing structural support and a stable base for the door itself. It is the vertical portion of the door frame that runs alongside the edge of the door and helps to hold it in place when closed. The door jamb is crucial for maintaining the integrity and functionality of the door, ensuring it fits securely within the door frame and opens and closes smoothly.


The door jamb consists of three parts: head, strike, and hinge jambs. The vertical sections, strike and hinge, are where the strike plate and hinges are attached. The head jamb runs horizontally, connecting the two vertical sides of a door frame.

There are three types of door jambs: rabbeted, split, and flat. Rabbeted jambs have a groove cut into the wood and come with a built-in stop. Split jambs are made of two parts to accommodate a thick and wide wall, while flat jambs are for matching a pre-existing standard doorway opening.

Wood is the standard material used for building a door jamb. Almost all residential houses have wooden jambs without a specific finish since they’ll be hidden once a casing or trim is installed. On the other hand, commercial settings call for building steel, aluminum, or fibreglass door jambs for long-term durability and weather resistance.

In addition to providing structural support, door jambs also play a role in weatherproofing and insulating the entryway. Weatherstripping, which is often attached to the door jamb, helps to seal any gaps between the door and the frame, preventing drafts, moisture, and outdoor elements from entering the interior of a building. This improves energy efficiency and enhances the comfort of the indoor environment.

Door Slab

A door panel without lites, a frame, or sweeps installed.

Door Sweep

Weather-stripping system installed at the bottom of a door; a sweep prevents air and water from entering the next room.


A space which protrudes from the roof of a house, typically 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, this involves two glass sheets separated by an air space within an opening to improve insulation against heat transfer and sound transmission.

In factory-made, double glazing units, the air between the glass sheets is thoroughly dried and the space is sealed air-tight, eliminating any potential condensation and providing superior insulation.

Double Hung Window

A window style that opens vertically on the top and bottom. These windows are best suited for rooms where you want to maintain privacy and have ample natural light and airflow. You can open the bottom sash when you need to cool a space, or the top when you want to vent warm air out.

Dry Glazing

An alternative method of placing glass in a door or window. Dry glazing is recommended whenever reflective coatings are glazed on the first surface.


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


Easy-Clean Glass

A specialty option that can be applied to the glaze; refers to the coating that helps prevent moisture and grime buildup. Rain that comes into contact with these windows will be sheeted off. This option is recommended for high up or hard to reach units.


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

Egress Code

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

Egress Window

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

Electronic Deadbolt

A type of deadbolt that features an automatic locking system. Electronic models come equipped with keypads that can store a number of code combinations for user convenience. They can be programmed to automatically lock when you leave your home, too. They feature all the same hardware as traditional deadbolts; the throw is released electronically, although it can be manually turned as well.


The measure of a material’s effectiveness in emitting thermal energy. In the case of glass, it refers to its ability to cool itself from sources of heat, such as the sun.

End Vent Slider

A window that features a fixed center sash, flanked by two sliding outer sashes. The sliding panes can be tilted inward for cleaning purposes; these windows are perfect for ventilating spaces. They are best suited where outside space would be compromised by an out-swinging window.


The ENERGY STAR® label signifies that a product, such as appliances, electronics, windows, and more, meets of exceeds energy efficiency guidelines set by the Environmental Protection Agency (EPA) in the United States. This label indicates that the product has undergone testing and verification to demonstrate its ability to significantly reduce energy consumption without compromising performance.

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For windows and doors, an ENERGY STAR® label indicates that these products have been designed and tested to effectively insulate against heat transfer, reducing energy loss and enhancing comfort. They contribute to lower heating and cooling costs while promoting sustainability by curbing greenhouse gas emissions.

Manufacturers and service providers can only display this logo on their products when they meet all ENERGY STAR® requirements. To earn an ENERGY STAR® certification, products must pass strict energy efficiency criteria set by the organization. These standards may change depending on what kind of product needs to be tested. During this process, a recognized third party manages the examination to ensure objectivity as they confirm if a product meets the existing standards.

Since its launch in 1992, ENERGY STAR® has made immense contributions to environmental protection. It continues to create a market of energy-efficient products, allowing consumers and organizations to use less energy while getting the job done. When shopping for products, the appearance of the ENERGY STAR® logo helps consumers make informed decisions about energy and cost savings.

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’s on the exterior side of the light or panel.


The process of shaping aluminum or vinyl by forcing it through a die, producing 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 commonly utilized in creating frame and sash materials, as well as glass insulating spacers and glazing sealers.


Failed IG Unit

An insulated glass unit failure is the industry term for permanent material obstruction of vision through the unit, due to the accumulation of dust, moisture, or film on the internal surface of the glass.


Fenestration refers to the arrangement and design of openings in a building, including windows, doors, and skylights. In Latin, "fenestra" means a small opening or pore in an anatomical structure and directly translates to "window."

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Fenestration serves two purposes: elevating the aesthetics of a building’s exterior and improving the indoor environment. Creating openings for doors and windows breaks the seal of a structure, creating paths for air to pass through. Having ample fenestration increases home comfort, enhances indoor air quality, and boosts energy efficiency.

Architects work hand-in-hand with window and door manufacturers, clients, and contractors to create a functional building design featuring the most ideal fenestration. Common types of fenestration include:

- Single or double hung windows
- Casement windows
- Awning windows
- Sliding windows
- Bay and bow windows
- Picture windows
- Transom windows
- Skylights

In essence, fenestration is a pivotal architectural consideration that balances practicality and design, shaping the interaction between interior and exterior spaces.

Fiberglass Doors

These doors are very durable and have a place in most households. They have the beauty of hardwood, but are not subject to dents, cracks, or splitting. The paneling designs on fiberglass doors can be custom-tailored for a unique finish!

Fire Rated Doors

A door constructed in such a manner to 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 Window

Windows that do not open; they feature a thinner frame and larger glass pane for maximum viewing space. ‘Picture windows’ can be installed anywhere; they provide maximum energy-efficiency due to the lack of an opening system, and are a great choice when you need to brighten a dark or small space.


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


Flashing is a crucial element in window installation designed to prevent water infiltration and moisture damage. It's a thin, flexible material, often made of metal, plastic, or rubber, applied around the perimeter of windows. Flashing serves to create a barrier that directs water away from the vulnerable areas where window meets the wall.

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Flashing is placed both above and below windows, along the sides, and sometimes integrated into the window's sill. It helps to seal gaps, channels rainwater and moisture away from the building envelope, and prevents leaks that could lead to structural damage, mould growth, and energy loss.

Properly installed flashing works in conjunction with other water-resistant components, like caulking and insulation, to ensure a tight and effective seal around windows, enhancing their longevity and contributing to the overall durability and efficiency of a building.

Window manufacturers recommend a specific sequence for flashing during window installation. While it’s possible to install window flashing on your own, it’s best to leave this task to the professionals. Their expertise makes them more adept and precise, preventing errors that may lead to costly expenses.

Flat Glass

All types of glass (rolled, float, plate, etc.) manufactured 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. This produces a high-optical-quality glass with parallel surfaces, without polishing and grinding.


The enclosure in which the window sash or door panels are mounted. Refers to the part the sash fits into (head, jambs and sill).

French Doors

Doors that open outward from one another; consist of two pieces that lock together when closed and swing out on a hinge. French doors are great for letting in light and airflow.

Full Screen

A screen which covers the entire opening of a window.


The process of heating mitered corners to 2008°F, 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.

Gas Fillings

Refers to the type of gas that is present between the panes of glass. Argon and krypton fillings are used often, as they slow down the heat transfer inside the glaze. This increases the energy-efficiency of the window better than windows that contain air.


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


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


The pane that sits inside the frame.


The process of sealing the glass to the sash. This can also refer to the number of panes that are present in the window. You can choose from double or triple glazed options; the latter is recommended for very cold climates, but most homes are suited for double glazed units.

Glazing Stop

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

Gliding Window

A window that opens horizontally; the panels slide left and right on a built-in track. Gliding windows are great space-savers and can be opened and closed with ease. They are recommended for use as an emergency escape window, due to the speed at which they can be opened.


Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being divided into smaller lites of glass. These are the bars that separate the glass into individual panes (the crisscrossing designs that many windows have).


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.


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; accommodates differences between opening and window heights.


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


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 a 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.


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


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

Internal Grills

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



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


The vertical sections located on both sides of the frame.

Jamb Extensions

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



The part of a window lock, mounted on an opposing surface of the window, that the lock arm locks under or into. Pulls 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, odourless, colorless, tasteless, non-toxic gas which is about 12 times more dense than air. Used to replace air between the glass panes, reducing temperature transfer and deters convection. Ideal when a higher performance is desired than panes 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’ indicates 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.

Lineal Footage

A dimension expressing length (in feet). 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.


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


A unit of glass in a window or door.

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, improving the U-value. The "E" stands for emissivity; Low-E glass comes in both soft coat and hard coat types. Soft coat units radiate better, as they consist of small metallic particles. Hard coats have a thin metal coating welded onto the pane.


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

Window and door frames fastened with screws.

Meeting Rail

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


Fabric made of fiberglass used in making screens.


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.


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 a unit to the rough opening.

Night Latch

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.


Crank-operated device used to open and close casement windows.



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


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.

Privacy Doors

These doors feature special glass designs that prevent people from peeking through them. They work great as entry doors, as the bevel designs are attractive yet functional.

Pull Handle

A handhold for sliding a 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.


An extruded or molded plastic material used for window framing.


Quarter Round Window

Stationary or operating window shaped as a quarter circle.



R-value, or “resistance value,” is a measure of the thermal resistance of an insulating material. It quantifies the material's ability to resist the flow of heat from one side to the other. A higher R-value indicates better insulation performance.

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It is used to evaluate the effectiveness of materials like insulation in buildings, with the primary goal of reducing heat transfer through walls, floors, and roofs. The R-value considers factors like thickness, density, and conductivity of insulating materials.

The formula for calculating R-value is R = Thickness / Thermal Conductivity, where the thickness is the thickness of the material in inches and thermal condictivity is a property indicating how well the material conducts heat. Building codes often specify minimum R-values for different parts of a building, helping to ensure energy efficiency and comfortable indoor environments.

For windows and doors, R-value is particularly important is assessing their energy efficiency. Windows with high R-values have excellent resistance to heat transfer, which lessens air leaks and sudden temperature changes. Installing windows with high R-values can provide lower energy consumption, improved insulation, reduced solar heat gain, and greater savings on electricity bills.

You’ll typically find an R-value number and description displayed on the energy labels of these products. If a window’s energy label doesn’t have an R-value, use this formula: R-value = 1/U-value. The U-value measures how quickly or slowly a window allows heat to pass through its surface. Using U and R-values, you’ll have a better understanding of how effectively a window insulates heat. Overall, a window with a high R-value and low U-value offers outstanding levels of insulation and heat transfer balance.


Wave energy transmitted directly from one object to another through the atmosphere or through transparent / 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 vapor or other liquid vapor begins to form on a cold surface. If the temperature changes, but no water vapor is added or taken away, then the relative humidity will also change, increasing as the temperature falls. The relative humidity will continue to rise with falling temperature until the dew-point is reached – or, the temperature at which the relative humidity becomes 100%.

Replacement Window

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


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


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

Roll-formed 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 where a window or door unit will be installed.


Safety Glass

A strengthened or reinforced glass that is less susceptible 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 aesthetic.


The components that hold a window glass in place inside the frame.

Sash Lift

A handle for raising the lower sash.

Sash Stop

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


Woven mesh of metal, plastic, or fiberglass stretched over a window opening to permit air to pass through.


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


Wood wedges (often wood shingles) used to secure the window or door unit in the rough or masonry opening in a square, for a 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, which lights an entryway or vestibule.


The horizontal section located at the bottom of the 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, simulating the look of a 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.


This is your standard door, minus the frame and weather-stripping; slab doors can be equipped with textures or left as a single flat surface; you can also choose to have glass inserts installed.

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.


A strip of material placed between two pieces of glass, maintains a uniform width between the pieces and prevents sealant distortion.

Square Foot

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


A blemish on a glass surface created by water or other solutions.


The vertical edges of a door window or screen. The bottom part of the frame; refers to the part the door slides against.


A trim member attached to the window frame, stopping 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 one another when opened.


Vertical wood framing members that create 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

Tempered glass is a type of safety glass processed and hardened by thermal or chemical treatments. It has various applications, including home windows, passenger vehicles, shower doors, and more. It’s four times tougher and stronger than a standard annealed glass, requiring extra power to smash it into pieces.

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The tempering process involves heating the glass inside an oven at 1,200°F. Then, manufacturers cool down the heated glass by rapidly blasting cold air onto the product. Doing so compresses the surface edges of up to 10,000 psi while adding tension to the glass’ inner layer. Because of this, tempered glass resists tensile stress and impact breaks.

Tempered glass splits into granular pieces instead of pointed shards when it breaks. This feature proves itself to be safe since it doesn’t harm those who get in contact with broken pieces. Its shatterproof and almost unbreakable feature also attracts homeowners to use it for their windows to prevent break-ins and burglaries.

Aside from that, professionals recommend using tempered glass in stressful areas such as high-temperature environments. Its resistance to wear and tear makes it a viable option for protecting people from sudden glass breaks due to heat.

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 temperature change.

Tilt Latch

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

Tilt-In Sash

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

Tinted Glass

Glass with material added, giving the glass a light and/or heat reducing properties and colour.

Total Unit U-Values and R-Values

The heat lost 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 efficiency.


A transom is a horizontal beam separating a door from a transom window placed above it, opposite the vertical mullion. This architectural feature is a popular customization choice, especially if you want to add flair to your house’s exterior. It can be as simple as a plain divider or as grand as a carved beam.

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This addition makes way for you to install a transom window, which is a fenestration product that’s available as a stationary or operable framework. Choosing the latter gives cross-ventilation to your home while maintaining privacy. It’s common in schools, apartments, houses, and office buildings.

Transom windows can come in unique designs based on your request. They may take a crescent or rectangular shape to fit the aesthetics of your house. You can even install stained glass or frosted windows for extra privacy. Installing transom windows typically happens during the design phase of a construction project. It’s when architects and engineers collaborate to see if it’s feasible for your house to have such an opening. However, it’s also possible to install this fenestration feature on existing buildings though it’ll take a lot of time, planning, and preparation for the project to be successful.

Transom Window

A large, fixed window. Typically 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).



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.



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

Venting Unit

A window or door unit that opens or operates.


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

Vinyl Clad

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

Vinyl Window

A window whose frame and sashes are made from vinyl.


Warm Edge Spacer

A non-conductive edge spacer found 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 is a material or a combination of materials used to seal gaps and openings around doors, windows, and other openings in buildings to prevent the infiltration of outdoor elements such as air, water, dust, pests, and noise.

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Weep Flaps

A vinyl flap covering a weep hole, which 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 glass to the sash.


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

Window Frame

The primary purpose of a window frame is to hold the glass or glazing of a window securely in place within the opening of a building's wall. It provides a rigid structure that keeps the glass panels in position and prevents them from shifting or falling out. The frame also helps to seal the gap between the window and the wall, contributing to weatherproofing and insulation of the building. It plays a crucial role in the overall stability, functionality, and aesthetics of the window.

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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 Sash

A window sash is a fundamental component of a window frame. It consists of the framework that holds the glass panes in place within the window opening. Sashes can be moveable or fixed, allowing for opening and closing. They're typically crafted from wood, metal, aluminum, or vinyl and may incorporate additional elements like grids or muntins for design and support.

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Single-hung windows use both types of sashes, while double-hung windows have two movable sashes. To lock a window sash in place, a sash lock hardware is installed.

When it comes to construction, a window sash is integral in keeping the window in place and maintaining durability. It should be air-tight, fusion-welded, and reinforced to prevent distortion over time. Otherwise, leaks and locking difficulties will occur, causing inefficiency in your home. The movable sashes should also be appropriately aligned with the window to prevent jams.

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.