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Window Performance: Are You Missing Something?

Strata and Property Management

What type of window is better? Last week for our LinkedIn initiative, #TwoCentsTuesday, we asked about the advantages casement windows have over sliding windows. Do they offer added water and airtightness? Increased insulating or structural performance?  

77% of you guessed that they offer all of the above, and in most cases this is correct… but not always! 

People tend to follow assumptions on window performance that is over 20 years old. Centra is working to break that paradigm and determine what modern windows are truly capable of. 

What we commonly miss 

We usually think of window performance as water and airtightness, and insulating and structural performance. One assumption is that casement windows always perform better than sliding windows in all areas of performance. However, sliders today aren’t like those of 20 years ago. Today, they can also be high-performing and efficient. A window’s performance covers several categories including a major one that is often forgotten: functionality.

When is a slider window better than a casement?


The location of the window is very important. If the window is meant to meet egress standards, then a casement would not suffice and therefore would not be a better performing window. Also, if the window is on the balcony deck and designed as a casement, it would take up deck space and could even be a hazard. A slider window is again a better option in this case.  

Visual Light 

Visual light isn’t something that is always considered, but it’s an important factor for some. Due to the smaller frame, a sliding window has more visual light transmittance when compared to a casement.

Don’t forget about Hardware

Hardware affects performance too. While casement windows usually seem to have the edge over sliders, performance is largely related to the function of the window and its hardware and this can make a difference. In this case, hardware also refers to the window’s PVC extrusion, as the performance will be affected by changes to its design. 

While casement windows with crank handles typically provide better airtightness, less water leakage, and higher structural stability than those with cam handles, medium to large size casements will have multiple cam handles and this can actually give better performance. Also, providing the hardware is not loose, the wedge action of the cam handle can generate greater force than the gear mechanism of the crank handle. The Benefit of the crank handle is that it locks in the open position with positive engagement, whereas cam handles lack that capability.

How do I select the right window?

  1. Consider all categories when it comes to window performance.

Don’t just limit your criteria to airtightness, water leakage, and structural performance. Always keep functionality in mind.

  1. Compare apples to apples

Casements vs. sliders is a good example of this. Casements perform better when it comes to water tightness, but there’s a catch: direct comparison of casement and slider windows of the same size is not applicable as half of the slider is fixed. If we take a 36x72 inch casement and compare it to a 72x72 inch horizontal slider, the casement has a significantly better water rating of 510Pa compared to 330 for the slider. This is attributed to the bulb seals on casements.

  1. Get an expert opinion

Selecting the right windows for your project will have a significant impact not just on cost and performance, but on the longevity of the building and the functionality for the end user. If you get a Window Geek involved early in the design phase, we can help you compare apples to apples and understand the impact your window selection will have on the short and long-term goals for your project.

We are your Certified Window Geeks

We love to talk windows! The demand for glass is at its all-time highest, but we are working with our customers to ensure you get the products you need. Contact us as early in the process as possible so we can help secure your order and keep your project on schedule. We will guide you early on so that your supply requirements are met. 

For more information on this topic (and many more!) contact our local Employee Owners at 1-888-534-3333 or drop us an email at Become a Window Geek yourself by signing up for our biweekly newsletter, which provides news, advice, and tips about the window industry and Centra events.

Written by: Les Ferris , June 3, 2022
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