From time to time, we Window Geeks hear the question: why are swing doors unlikely to achieve a fenestration Performance Class of CW? Why might a swing door achieve a Class LC when it passes a deflection limit of L/175, as opposed to a Class CW?
Let’s start with some lingo…
Performance Class LC: Common in low and midrise multifamily buildings where larger sizes and higher loading requirements are expected
Performance Class CW: Common in low and midrise buildings where larger sizes, higher loading requirements, limits on deflection and heavier use are expected
If we take the NAFS lab test results we gathered on a standard door width of 36” x 96” (a commonly used door size in a home) you may notice that it achieved a designation Class LC – PG70.
It is important to understand that for decades, door sizing has been structured around stock door slab sizes. This limits the sizes available in the market, but as we progress with doors, we have started making them similar to windows with custom sizes being more readily available. This has been facilitated by the transition from a fibreglass/wood system to a PVC system similar to windows. Previously door sizing has always been standardized, which is why the 36” x 96” door size was selected in our example.
What is interesting about these results is the deflection data contained in the report. We see below that the Uniform Load Deflection Data indicates the length of the tested product is 2311 mm (the L in the deflection limit of L/175). When you divide 2311 by 175, you get 13.2mm of allowable deflection. You can also see that during the test, the amount of deflection was 4.53mm. Based on this logic, the door meets L/175, and should be classified as Class CW, but it is reported as Class LC. Why is this?
It has to do with the gateway sizes. The size of the door tested was 920mm x 2440mm, and based on this, it does not meet the gateway size listed in table 12.2 of the NAFS standard. Therefore, it was designated Class LC despite meeting the L/175 requirement.
When evaluating product or deciding what size of product you want to test, it is important to consider the gateway sizes as a minimum for the result you are trying to achieve. Also, if your concern is deflection, focus on that as your review and not simply on the Performance Class of the product.
To sum up, the reason why most doors never achieve a CW class is because the stock door slab size that can be used is not large enough to meet the gateway size. However, as doors transition to similar methods as windows, sizing becomes more customizable and building a door wider than the standard 36” is achievable.
If you’re still confused, don’t worry! Just get in touch at Jacquiev@centra.ca and we’ll be happy to answer any questions you have.
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