22 l ROOFINGBC l WINTER 2018 TECHNICAL UPDATE zones should be). This is the minimum requirement. The specification also may indicate what type of roof assembly is acceptable (MARS, PARS or AARS), or even what type of membrane should be used, but this is as specific as it may get; in a descriptive approach, the choice of a satisfactory roof assembly generally is left to the roofing contractor. To ensure the end result matches the desired outcome, the Design Authority can insist that the roofing contractor provide a written system description and securement details to a consultant or the general contractor for review and approval prior to construction. A descriptive specification can be as open-ended as the designer feels comfortable with, but the key to under- standing this approach is that it removes certain decisions from the Design Authority and provides for a variety of solutions. That sounds great, but broader parameters may result in bids that are “apples to oranges,” or remove from the Design Authority some control over the project, or it may produce undesirable results. For example, the Design Authority may wish to assign to the Contractor all the responsibility for engaging a Professional Engineer (and for providing all supporting schedules) to design the makeup and securement of the roof assembly. But this may mean the Design Authority forfeits any control over the performance and appearance of the assembly, and it complicates the entire building design when it comes to meeting the energy performance requirements of the structure as a whole (think envelope first as a guiding prin- ciple of the BCBC). Often, it simply is better to keep all that work in-house, if only because it simplifies coordination and code compliance. Common Mistakes At the RCABC, we review many specifications. We do this as a service to specifiers, and we review specifications when our Members come to us with questions during the bid stage and in mid-construction. In our unique role, we see a range of specifications, and while many of them are good or even great, some of them reflect the haste and uncertainty of the writer. When a specification fails to clearly articulate the requirements for the job, it engen- ders confusion and can result in costly “extras” because of contradictions within the specification, or because of misapplied terminology. Try to avoid these common mistakes when it comes to wind-resistant roofs: •  Avoid referring to “FM” standards (usually the so-called FM 1-90), because FM standards are not rele- vant to comply with the BCBC, they are specifically for FM-underwritten projects, and when FM is listed it may be impossible to comply with both FM and BCBC requirements. •  Don’t state the wind speed the roof assembly should be rated for. Wind velocity is only one factor in deter- mining upward (negative) wind pressure, which is the measure- ment required by the BC Building Code. Wind velocity by itself is meaningless when considered out of context. •  Be careful about including “CSA A123.21” in the References subsec- tion of the specification, unless you are actually going to specify a Tested Assembly. CSA A123.21 is a standard for how to test the wind resistance of membrane roof assemblies, and is often mistaken as the standard for wind resistance. No one but a qualified facility can actually perform the test. •  Resist specifying securement details like fastener penetration depths or adhesive ribbon applications. These details normally are listed in any Tested Assembly report, or as part of an assembly with Proven Past Performance, or should be incorpo- rated in a custom-engineered roof assembly. Details like this are also dictated by some material manu- facturer’s minimum requirements in order to achieve a desired rating. Request a Quick Quote Toll-Free: 1-877-505-5003 www.KeeSafety.ca Separating People from HazardsSM KeeGuard® is a modular safety railing system that can be designed to fit virtually any flat or low-sloped roof. • Does not penetrate the roof membrane • Easy to install - no welding or drilling • Corrosion resistant FallProtectionfortheSize &ShapeofYourRoof Meets or Exceeds OHS and Provincial Regulations