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Windows elevate our everyday by bringing in natural light while keeping away harmful insects and controlling adverse weather conditions.  Windows are tiny parts of a house, but the window terminologies can be overwhelming, especially for non-industry players. That’s why we’ve taken it upon ourselves to explain some of the technical window terminologies we use in new construction, remodels, and replacement projects.

Common Window Terms Explained


American Architectural Manufacturers Association. The nonprofit trade association that sets quality standards and provides various educational programs and events for the window, door, and skylight manufacturers.

Annealed Glass

Annealed glass is manufactured by slowly cooling to relieve internal stress and prevent cracking when exposed to temperature changes. Unlike tempered glass, annealed glass often breaks off in large, sharp pieces hence not suitable for high traffic areas or windows accessible by young kids. They are great for basement windows because they’re relatively cheaper than tempered glass.

Air Infiltration (Air-Leakage)

The measure of the amount of air leakage passing in and out of a building’s structure through windows, doors, skylights, poorly sealed access plumbing access points, siding cracks, etc.

Air-Leakage Rating

A measure of the rate at which air is leaking around a door or window or door. The measurement is calculated based on the building’s relative interior to exterior air pressure. The rating is used to determine how air-tight the building’s doors and windows are.

Ambient Temperature

The environmental temperature of the immediate surroundings.

Argon Gas

Argon is a gas fill used by window manufacturers for displacing the air trapped between the panels in windows. Constituting about 1 percent of the Earth's atmosphere, Argon is non-toxic, clear, odorless, and inert.

Astragal Balance

A vertical hardware piece designed to be fastened to a door for the purpose of sealing the gap between double doors when the doors are closed.

Basement Window

Any window located in a basement for the purpose of light or ventilation of the space.


A window balance refers to the hidden window components fitted inside the window frame. They are only used in single windows or double hangs to assist you with the sash’s weight when closing or opening the window.

Bay Window

An assemblage of a picture window between two smaller windows that are angled to create a bay space on the interior side.

Bottom Rail

The horizontal section at the bottom of a window sash.

Bow Window

An assemblage of four or more windows positioned to form an arch-shaped window unit bowing outward from a building.


A molding designed to use as the casing for the exterior side of a window or door.

Blind stop

A blind stop is a rectangular molding used in the construction of window frames. It’s often nailed between the outside sashes and the outside trim piece and serves to stop the sash or the screen.

Cam Lock

A cam lock is a small piece that pulls together your window sash to keep the window locked and secure. They’re available on both single hung and double hung windows.


A casing is a piece of molding often used to trim the window’s perimeter. Cases are narrower but much thicker than base moldings.

Cable Support Kit

A set of hardware made for anchoring a bow or bay window to a building’s structure. The kit is designed to support the part of the window that extends outward to prevent it from sagging.

Casement Window

A window with hinges on both the interior and exterior sides, designed so that the sash swings open in the outward direction for ventilation.


A construction compound made for sealing crevices to prevent air or water leaks.


The accumulation of water on a window, wall, drinking glass, or other surfaces due to humidity in warm air converting to water droplets when it meets the colder surface.


The process or effects of deterioration of stone, metal, or other material from a chemical reaction due to exposure to moisture, weather conditions, corrosive chemicals, or other causes.


Window cladding refers to wood windows enclosed in another material or made with an external application of another material like aluminum, vinyl, PVC, or fiberglass.


Composite windows are manufactured with several different materials in a compact combination to give the window the look and benefits of many window types.


Interior window condensation occurs when there is excessive moisture in the house, usually during winter. Exterior condensation occurs when the window surface is cooler than the dew point.


Conduction is one way through which heat passes through the window and involves the passing of heat through a solid material (window frame and glass) from molecule to molecule.


Convection is the heat transfer through the movement of gases or liquid. Warm air in the room touches the cold window and cools down and sinks, which creates a convection current of air around the window.

Double Glazing

Double glazing is sometimes referred to as Insulating glass (IG), and consists of 2 or 3 glass window panes that are separated by a gas-filled space or vacuum to minimize heat transfer across the window.

Double Hung Window

On a double-hung window, both sashes in the window frame are operable by moving up and down. They allow the sashes to tilt easily for easy cleaning.


Egress windows are large windows that allow room occupants to enter or exit during an emergency. They’re required when finishing a basement and are often attached to ladders or steps for an easy escape.

ENERGY STAR® Certification Program

ENERGY STAR® Certification Program streamlines window manufacturing by ensuring that windows are manufactured by ENERGY STAR qualified windows manufacturers and the products are independently tested, verified, and certified by the National Fenestration Rating Council (NFRC).


This is a process of extruding molten raw material through a set of metal blocks (dies) to produce a vinyl profile that is then cut into specific lengths and welded together to form a window system.


Fenestration is a term used to refer to the design, construction, or openings in a building. They include windows, doors, wall panels, vents, storefronts, louvers, and much more.

Window Head

This is the main horizontal part that forms the top of a window frame.

Insulating Glass

Insulating glass (IG) comprises two or more window panes separated by an insulating material like a vacuum or gas.


This is a putty or glazing compound that holds the window glass in place and seals off external weather conditions.


Window Grilles refer to decorative patterns on a window or door and consist of horizontal and/or vertical bars dividing larger sheets of glass into smaller window panes.

Jamb liner

A jamb liner is helpful for extending the interior of your window so as to cover the thickness of the walls and transition between your interior trim and the window.

Krypton Gas

Krypton is a non-toxic, odorless, colorless gas that is used in place of air between window panes to improve insulation and energy efficiency.

Lead Safe Window Replacement

Lead safe is a certification requires as per the federal government law passed in April 2010 that requires all homes constructed before 1977 to adhere to practices that ensure minimal exposure to harmful Lead.

Low E Glass

Low E Glass is manufactured with advanced technology to keep your home warm during winter and cool during summer. The glass comes with 3 coats of silver on the outside to insulate your home from the outdoor conditions.


A mullion refers to a vertical element that divides different window or door units and is mainly meant for decoration.

National Fenestration Rating Council (NFRC)

The NFRC serves to provide doors and windows retailers with facts sheets to educate their clients during purchase.

Obscure Glass

It’s any type of rolled glass with an embedded pattern on its surface. Some types come as painted or laminated glass used for decoration purposes.


A pane refers to the glass part of a sectioned window.


A plumb refers to the vertical planes in a window.


R-value is the resistance of a window to heat conduction and is expressed as the inverse of the U-factor.


Rails fit between the vertical components of a window. They are the horizontal members of the sash.

Replacement Window

This is a window that is fitted to an existing window opening to replace the existing window.


A retrofit window is installed into an existing window frame.

Roller Cams

These are universal products that suit most UPVC profiles of window or door locking systems to provide a secure locking point.


A sidelight is a window with a vertical emphasis, usually flanking a door or a larger window.

Slider Window

A sliding window is utilized in wider and shorter openings. The windows often open sideways with one pane sliding over the other.

Solar Heat Gain Coefficient

Abbreviated as SHGC, Solar Heat Gain Coefficient denotes the fraction of solar radiation that goes through the window. It is usually expressed as a decimal number between 0 and 1.

Tilt and Turn Windows

Tilt and turn windows operate in two ways. As the tilt opens the top of the sash towards the inside for ventilation, the turn creates an opening side hung to the inside.

Window Sash

A window sash comprises one or more movable panels that hold panes of glass.

Sash Lock

This is a window latch and keeper used to lock sliding windows.


A windows operator features a worm gear driving mechanism with a steel arm and is often used in steel-framed windows.

Side Jamb

A side jamb is the side-post or lining on a window or doorway.

Single Hung Windows

A single hung window has the top sash fixed in place and does not move while the bottom sash is freely operable.

Tempered Glass

Tempered glass is a tough safety glass that is 4-5 times harder than regular glass and is made under extreme heating followed by rapid cooling. When it breaks, it shatters into little pebbles that pose less danger.

Vinyl-Clad Window

Vinyl-clad windows are made with wood interiors with an external vinyl cover to improve durability and longevity while giving the interior the aesthetic finish of the wood.

U- Factor

U- Factor is the measure of the rate at which heat is transferred across the window and tells how well the window insulates. It ranges between 0.25 and 1.25 and is measured in Btu/h.

Warm-Edge Technology

Warm Edge technology uses spacer bars to insulate the edges of sealed window units to keep the panes of glass apart and reduce heat loss.

Weep hole

This is a tiny hole located at the bottom edge of a storm-window frame to drain off water from the window and prevent the wood from rotting or steel from rusting.

Get Energy Efficient Windows in Utah from Advanced Window Products

Advanced Window Products is the #1 window replacement company in Utah. Known to challenge industry standards, we strive to provide durability, aesthetics, and great designs. We provide high-quality window products for vinyl sidings and energy-efficient replacement windows. Visit our showroom in downtown Salt Lake City or give us a call for a free estimate at your home. We manufacture our own products and sell directly to our clients. We even do the installations, so no room for middlemen.

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