Window Terminology You Need to Know

For the uninitiated, window terminology can be a bit of an ordeal to figure out. There are all sorts of specialty words, acronyms, window types, and organizations involved in the terminology that can seem, to outsiders, like a whole new language.

window terminology

While this is by no means an exhaustive resource for everything you’ll come across, this list will give you a brief overview of some of the more common words associated with windows.

American Architectural Manufacturers Association (AAMA)

Established in 1936, this national trade association sets standards for the door, skylit, and window industries. Being a material-neutral organization, their goal is to influence the construction codes of windows.


The area on the window underneath the stool that is usually made of a decorative trim.

Arch Window

A window with a curve on a top and rectangular lower half that is made from four panels. Also called a radius window.

Awning Window

awning window

This type of window has a top hinge that allows the sash to swing outward from the bottom. These types of windows are typically used in conjunction with other window styles.

Basement Window

This type of window is located in the basement and is typically intended for ventilation and natural lighting. Many building codes require it to be the correct size as an emergency escape route.

Bay Window

This type of window is built usually as a semi circle and protrudes from the house, consisting of three or more units.


This is the area where the frame overlaps the glazing – can be located on either the inner or outer edge of the frame.

British Thermal Unit (Btu)

The heat needed to raise one pound of water by one degree, also equivalent to 1.055 x 103 joules. Despite its name, it’s only used in the United States. BTUs are used to quantify the amount of energy retained in windows and other units.

Casement Window

casement window

A window with all of its hinges located on one side, and held open with a stay – because of this these windows open horizontally.


The decorative molding that goes around the inside of the window, covering up the ugly rough parts between the window frame and the wall.

Colonial Window

A specific style of window known for their multiple smaller panels of glass.


This is when warm, moist air comes into contact with a cooler object like a mirror or window, resulting in a collection of moisture on the object.

Condensation Resistance (CR)

In windows, this is a measurement of the interior resistance to condensation. Represented by a number, the CR can be anywhere from 1 to 100 – with higher numbers meaning a higher resistance.

Design Pressure (DP)

Regulated by the AAMA and the WDMA (Window and Door Manufacturers Association) this is a rating calculated to measure the relative pressure a window can withstand.

This is tested by clamping the window to a wall, reducing the interior pressure – and thus increasing outside pressure – and recording the amount of time it lasts without permanent damage. Typically, the DP rating is anywhere from 30 to 60.

Dual-Action Window

A window that can tilt both outwards horizontally or inwards vertically. Also called a tilt-turn window.

Energy Star

Energy Star stems from the U.S. Environmental Protection Agency as a way to categorize certain appliances and construction designs as energy efficient. For windows this means how much light is let in, along with how well insulated it is.

Four different standards have been set based on the four different climate zones in the United States.

Forced-Entry Resistance (FER)

This is a window or door that can withstand resistance from forced entry in the locked position. FER approved glass is usually made of multiple layers of glass and plastic.

French Casement Windows

These types of windows have hinges on opposite sides and open outward without any adjoining middle post.

Gateway Performance Requirements

This is a combination of all the minimum requirements for a set door, window, or gateway – this includes everything from forced-entry resistance, structural design load, water penetration testing, and several other factors.

Heat-Strengthened Glass

Heat treated glass that has been compressed to a certain strength based off of ASTM C1048. When compared to other types of glass with similar thicknesses and pressure loads, heated glass was rated as twice as strong.

Leadership in Energy and Environmental Design (LEED) rating system

A worldwide green rating system that works as way to reduce the environmental impact of human beings. Originally created by the U.S. Green Building Council (GBC), this program has recently expanded to residential projects as well.

Low-E Glass

This type of glass reduces heat loss with a microscopic clear coating that reflects infrared energy in the form of heat. Low-E glass has been shown to increase the insulation and energy efficiency of a home.


This is the section where two or more windows are joined together – this joint can be either horizontal, vertical, or both.

Negative and Positive Pressure

Pressure that pushes outward from the inside is classified as negative pressure. Pressure that pushes inward from the outside is considered positive pressure.

Pivot Window

This type of window moves either horizontally or vertically – rather than using a hinge it typically uses points on the frame to move.

Pressure that pushes inward from the outside

Shading Coefficient

A decimal value that is derived from dividing the solar gain of a single-glass window into that of the solar gain of any particular window. Double-glazed windows for instance, have a shading coefficient that ranges from 0.85 to 0.9.

Sound Transmission Class (STC)

Calculated based on ASTM E413, this class is based on how well sound is insulated in the interior. Based on typical indoor office noises, this is a single number rating.

Splayed Window

A window that is located at an angle in the wall.

Storm Window

Also called a secondary window, these are located outside of the normal window for additional protection against storms and insulation during winter.

Tempered Glass

Heat treated glass that follows in concordance with ASTM C1048. This type of glass has about four times the strength of similarly thick, untreated glass. When broken, this glass will break into multiple small cubed pieces.

Thermal Barrier

This is a piece of material with low thermal conductivity that is put between two materials that have high thermal conductivity in order to reduce heat loss and transfer.

Venetian Window

A large, arched window that has two smaller and narrower rectangular windows on either side. Originally pioneered by the architect Andrea Palladio in the 16th century, it is also called a Palladian window.


A resistant material that is made from polyvinyl chloride (PVC).

Know Your Window Terminology

While it may seem like a lot to take in, it’s important to understand the different terms associated with your windows. When you know certain things about your windows, you can better describe and identify any problems that may arise.

In such cases, you may need to replace your windows. When the time comes for replacement, look no further than Feldco. Over 350,000 homeowners have trusted us with their home improvement projects and we’d love to help you with yours – get a free quote now.

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