www.rcabc.org  l  31 TECHNICAL UPDATE Incorporating wind resistant roof design in project specifications To ensure a project is constructed as easily as the previous three steps, project specifications should clearly and unam- biguously articulate the requirements. There are two essential approaches to specify the application of the NBCC and RoofStar Guarantee Standards: the prescriptive approach or the descriptive approach. The prescriptive approach is really the traditional method of specifica- tion writing. In this approach, the Specification lists the materials to be used, perhaps together with approved alternates (commonly done). The Design Authority must include the following in the project specification: 1.  List the Specified Wind Loads for the roof 2.  Provide details of the Roof Securement Design, either by a) Identification of a specificTested Assembly that matches the listed materials, or b)  A clearly described assembly with “Proven Past Performance,” supported by design calculations and clear fastening patterns and descriptions. These proven assemblies are typically offered by manufacturers who are confi- dent the assembly will meet the Specified Wind Load calcula- tions for the roof (also a provi- sion in the NBCC) c)  Description and details of a specific securement system designed by an engineer to meet or exceed the wind load calcula- tions using ANSI/SPRI WD-1. In the descriptive approach, the Design Authority may elect to specify only the wind load requirements, roof system, and attachment methodology (MARS, PARS or AARS), and leave the selection of securement to either an engineer or the roofing contractor. In any event, secure- ment details, inclusive of clear fastening patterns and descriptions, should be submitted to the Design Authority for review and approval. Certainly, a specification need not be wide open for interpretation by the contractor and could include some parameters, such as restrictions on the type or brand of membrane and insulations. Installing the Roof Once the design is complete, the roofing contractor is obligated to install the specified roof system and its secure- ment design. Project specifications need to provide sufficient detail for the contractor to work with, including copies of test reports and fastener or adhesive pattern diagrams. Not in Kansas anymore, Toto: looking ahead Our climate is changing. A 2017 report produced by Metro Vancouver indicates significant climate and local weather pattern change over the next three decades, affecting mean seasonal tempera- tures, wind and rainfall. Similar changes are anticipated for other regions of British Columbia, and we are witnessing consid- erable climate shifts across the province, and across the continent. We already know that wind events are stronger than they were one or two decades ago, even if their frequency seems no different. Designing a roof to meet the demands of the future is what we are about. Our RoofStar Guarantee Standards are as dynamic as the climate we live with. Watch for further changes to our Guarantee Standards as we work with the NRC to develop new, improved wind resistance standards to ensure roofs stay where they’re built. Read the full article published as part of the Roofing Practices Manual, online at rpm.rcabc.org/, or find it on LinkedIn. We’ve authored the book on great roofing design standards. Learn more about our RoofStar Guarantee Program at www.rcabc.org. James Klassen is a RoofStar Technical Advisor and staff writer with the Roofing Contractors Association of British Columbia. He is an experienced roofing estimator, Occupational Health and Safety professional, independent Insurance Claims Adjuster, and Facilities Manager for a large private school in British Columbia’s Fraser Valley, overseeing facilities maintenance, grounds management, custodial services, school transportation and driver education, and capital projects.