Brands of composite decking and PVC decking now commonly promote themselves as having Class A Flame Spread Resistance. I know that sounds good, and Class A is probably better than Class B, but does it really mean anything? Essentially, no.
There is a standard (a standard and a test method are two different things - one is a requirement, like windows having a certain impact resistance in hurricane prone areas, and the other is a way to make sure two different labs can test the window for impact resistance and get the same result) for decking in Wildland-Urban Interface areas in new construction in California. But it doesn't have classes - it's pass/fail. Either you meet the the minimum requirement or you don't, and in fact a lot of decking that does meet it is ASTM E84 Class C. Here's an excerpt from a paper on this subject written by one of UL's top engineers:
There is no correlation between Steiner Tunnel FSI ratings and effective PHRR as measured by the Under Deck test.
• Class A Steiner Tunnel FSI rating does not guarantee California WUIBS fire compliance.
• California WUIBS fire compliant deck boards may exhibit a Class C Steiner Tunnel FSI rating.
So what is Class A? Well, there are Class A motor homes (a real big one), there's Class A office space (real nice, maybe too nice), and Class A driver's licenses (you can drive the big rigs), and of course Class A jerks (although, jerks are more commonly classified by number - first-class jerk, for example). But there isn't Class A decking.
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Decking will have a flame spread rating, but a ‘Class A’ flame spread rating isn't enough to qualify as a compliant decking product in California (according to the provisions in Chapter 7A of the California Building Code) and so in that respect, the flame spread rating doesn't matter. The flame spread rating can affect the type of siding that can be applied adjacent to the deck. If the flame spread of the decking is Class A or B, then any siding product that complies with any of the Chapter 7A ‘siding’ provisions is ok. If the flame spread rating is Class C, then only noncombustible or ignition resistant material can be used within 10-feet of the deck. An ignition resistant material is one that has passed the extended (i.e., 30 minute vs the 'normal' 10 minute) flame exposure described in the ASTM E-84 flame spread test (ASTM E-84 Standard Test Method for Surface Burning Characteristics of Building Materials), after a prescribed accelerated weathering procedure. Therefore, with a compliant decking having a Class C flame spread, untreated wood siding, vinyl siding, or log wall siding, for example, couldn't be installed within 10-feet of the deck. In California, if a decking manufacturer chose not to conduct a flame spread test, but had product that otherwise complied with the provisions of the code (i.e. met the required heat release rate requirement with tested to State Fire Marshal (SFM) Standard Test 12-7A-4) , then a Class C flame spread would be assumed, and the allowable siding would be restricted.
ReplyDeleteAlso, I checked out your ‘promote’ link. It goes to a TimberTech website, as you know. There is a photo of deck at that site, and ‘Class A Flame Spread’ is written on the photo. I think the main point of the site, however, is the statement ‘TimberTech Decking Meets California Fire Codes’. Some of the TimberTech products have a Class B flame spread rating and some (the PVC products) have a Class A flame spread.
For those interested in finding other decking products that comply with the California code, you can download the Wildland Urban Interface (WUI) Products Handbook on the California Office of the State Fire Marshal website: (http://www.osfm.fire.ca.gov/strucfireengineer/pdf/bml/wuiproducts.pdf). The document is free.
Steve Quarles
University of California Cooperative Extension