Commercial window replacement projects are involved, and the type of window that’s installed on a property must be specific performance grades. Introducing a product without the correct window performance specifications can cause many problems – from structural issues to energy performance problems.

That’s why every commercial window installation project starts with an analysis of the building. Low- and mid-rise buildings have many different needs compared to residential buildings, and therefore, attention must be paid to the types of windows that are installed.

Commercial windows used on low-rise properties, for example, are much greater forces of pressure, wind-driven rain, and structural strength. A question we often receive is what exactly is window performance, and why does it matter? We’re going to take a quick look at different performance grades, and what they mean for your property.


Energy performance. Energy performance is crucial for commercial windows. Matching a window with the right energy performance rating to a property can help to balance solar heat gain and heat loss, which limits the heating and cooling demands on a property.

Some factors are used to determine the energy performance rating, including SHGC (solar heat gain coefficient), U-value, which is how well a window conducts heat, as well as condensation resistance and visible transmittance. Ultimately, window installation companies carefully select products for a property depending on how much direct sunlight it receives.

Performance grade. Alternatively, performance can refer to design pressure (which is referred to in the industry as “performance grade). There are four performance classes, R, LC, CW, and AW, and these classes refer to the type of property a window is designed for.

LC and CW windows, for example, are rated for commercial properties, especially low- and mid-rise buildings. To achieve a specific class, a window must meet the minimum performance grade ratings for the class.

Performance grade includes many pressure, structural and water penetration tests. For example, the structural pressure must be 150 percent of the design pressure for commercial windows. Similarly, the window must achieve a certain percentage of design pressure to pass the water penetration test. Performance grades also take into account some other variables including air infiltration, forced-entry resistance, and uniform load deflection testing, among others.

Why Performance Grade Matters?

For commercial property owners, window performance ratings matter for many reasons.

Pressure. Most importantly, window performance ratings help to protect the structural integrity of a property. Wind pressure is much stronger on commercial properties, especially mid-rise and high-rise buildings. For example, the downdraft effect is caused when the wind blows directly at a mid- or high-rise building. The wind has nowhere to go, so it’s pushed downward, exerting significant pressure on the low-story windows.

Therefore, installing the right type of window will prevent damage from occurring, due to this heightened pressure.

Wind-Driven Rain. Because of the higher pressure, rain hits larger buildings with much stronger force. Therefore, the right performance rating ensures a building is protected from water entering in through the windows.

Thermal Performance. Windows can significantly affect the energy performance of a building. In fact, as much as 30 percent of heat loss can be attributed to inefficient windows. Therefore, energy performance grades help installers choose the right products for achieving specific efficiency goals for the property.

These are just a few examples of how window performance can affect a commercial property. There are numerous other instances. For example, in hurricane-prone areas like the coastal Mid-Atlantic states and Florida, windows must be hurricane-tested.

What You Need to Know About Window Performance

Ultimately, window performance is a tough concept to grasp. There are just so many standards and tests. For most people, it can be a challenge to get the hang of the lingo. If there’s one thing to remember, though, it’s this: Window performance grades protect the structural integrity of a property. They make it possible for installers to choose products that are specifically designed to meet the energy and pressing demands of a property.