Codes and standards
You Bet Your Glass: June 2013
A standard too far
June 14, 2013 By Frank Fulton
When NAFS is more widely specified, many manufacturers will be finding
out that the new standard is so very different from the A440 that they
will have to re-test their entire product offering to comply.
When NAFS is more widely specified, many manufacturers will be finding out that the new standard is so very different from the A440 that they will have to re-test their entire product offering to comply. I anticipate that a lot of manufacturers may be irate at what will soon be coming their way.
The new NAFS looks an awful lot like the AAMA standards of the past. Having done a lot of window business south of the border in my former role at Fulton Windows, I became very familiar with the AAMA standard and developed a big dislike for it. I found that the rules and procedures and the way users applied the standard to their project specifications made it necessary to greatly overdesign products to comply, in particular the structural requirements.
Instead of having one test size per product to comply as we did with the A440, NAFS has four categories or “performance classes”: Residential (R), Light Commercial (LC), Commercial (CW), and Architectural (AW). In each category, the criteria are more stringent, but the major difference is that the test size of the window or door gets significantly larger. The test sizes under the A440 were reasonable and reflective of what could be expected in the marketplace. The test sizes for the CW rating are way overboard and for the AW rating are outrageous, in my opinion. In order to have a product rated to one of the performance classes, it must pass testing at a prescribed “gateway” size. Downscaling to achieve a performance class rating is not permitted.
Under A440, windows and doors in a ten storey building located in all major centres from British Columbia to Quebec would require a structural rating of C3, meaning that a window could not blow out or fail to operate at a force of 3,000 pascals, equivalent to a wind speed of 245 kilometers per hour, or deflect more than L/125 at a force of 1,200 pa. For a one-metre-high sliding window, the maximum the meeting rails were permitted to bend was eight millimeters. For a sliding door the blow-out limits were 2,500 pa and the deflection limits were L/175 at a force of 1,000 pa with an allowable bending limit of the meeting rails at 11.7 mm.
Under NAFS, the structural load test for windows in a 10 storey building in major centres is different from city to city. The blow-out pressures are in a range between a low of 1.56 kPa for Montreal to a high of 2.15 kPa for Quebec City. The testing for resistance to blow-out is less stringent under the new NAFS standard.
The problem for manufacturers will be to meet the new deflection limitations imposed by NAFS due to the considerably larger test sizes and heights in particular but also because of higher imposed loads and more stringent limitations in the case of windows. As an example, for windows and doors installed in a ten storey building in either Toronto or Quebec City, the test for deflection would be conducted at 1,430 pa with limits of L/175. Factoring the size, load, and deflections limitation differences on the meeting rails, the test on a sliding window under NAFS-CW is 328 per cent more stringent and for a sliding door 79 per cent more stringent than under A440 and CGSB 82.1-M89.
To meet the new CW rating, all existing sliding window and door meeting rails must be re-designed and reinforced significantly. The absurd thing in all of this is that a slider has to be designed strong enough to pass a test at a height of 1,500 mm, but in reality most sliding windows provided to mid-rise buildings are only about 500 mm high. In other words, the new standard will be responsible for over-engineered products and greater building costs.
Frank Fulton is president of Fultech Fenestration Consulting. He has been in the industry for 30 years and can be reached via e-mail at firstname.lastname@example.org.
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