www.rcabc.org  l  19 TECHNICAL UPDATE R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com R E L I A B I L I T Y S T A R T S A T T H E T O P Serving Southern British Columbia Since 1976 COR Safety Certified P: 250-492-7985 • F: 250-492-7781 • E: interiorroofing@shaw.ca • www.interiorroofing.com leaving that to industry self-regulation1 . In its previous iterations, the BCBC provided the Design Authority with two optional pathways for compliance: a)  the “prescriptive path” in which the building design and construc- tion had to ensure that the build- ing’s individual components met certain standards for strength and performance (measurable through standard testing); or b)  the “performance path,” in which the building was treated as a whole, or “system of systems,” where every component was evaluated in its relationship to all the others (an example would be a window’s effi- ciency in relation to the control of air and water vapour throughout the rest of the building envelope). The prescriptive path was always the easiest to follow, and so most design specifications followed that path, and most builders built a building to comply with the prescriptive requirements of the BCBC. In some respects, the BCBC made an artificial separation between structural requirementsandthestandardsforsafety, comfort, accessibility and energy effi- ciency, which includes any requirements for building envelope performance. The 2018 BC Building Code changed all that, and the design and construction of roof assemblies is where it is most noticeable. A roof structure is no longer supposed to resist primarily gravitational loads (dead and live loads that exert a downward force on the structure) but 1 The RoofStar Guarantee Program is a QA/QC program operated by the RCABC. must also resist the upward (and poten- tially destructive) forces of wind. These forces can tear open a roof assembly and compromise the water, vapour and air control layers in a building. Consequently, the Design Authority must now understand and apply together the BC Building Code requirements found in both Part 4 (Structural Loads) and Part 5 (Environmental Separation). This is a unique and potentially compli- cated marriage within the Code. The very thought of being responsible for both Part 4 and Part 5 requirements can induce an aneurism in some designers; but it reflects the new focus on perfor- mance-based building design, rather than the prescriptive approach. It is potentially complicated because it means the roof assembly design for environmental separation (keeping water out, regulating the temperature of the conditioned space and controlling the passage of air and vapour through the envelope) must be able to resist those upward pulling forces that wind exerts on a flat roof surface. This was not contemplated in the old BCBC require- ments. But this new union between Parts 4 and 5 is complicated only when the building is particularly tall, or where it is unusual in its design. In nearly every other instance, there are tools and templates available to the Design Authority so that a roof assembly can be easily designed to satisfy both. Of course, the structural calculations remain the responsibility of a Professional Engineer. Setting that aside, however, the Design Authority may choose one of two general pathways for specifying the roof design so that, in simple and effec- tive ways, the architect can communicate clear and unambiguous intentions for a secure, weathertight roof that serves the rest of the building envelope. Choosing an Approach: Two Pathways There are two fundamental approaches to specifying the application of the BCBC (or NBCC), which our RoofStar Guarantee Standards support and enforce: