Evaluation of a new standard
The design and construction of roof assemblies for buildings in Canada are no longer a simple composition of layers of roof components, relying on the proprietary design of the system by the manufacturer. The low-slope roof assemblies, excluding protected roof membrane assemblies, built in Canada as per the building code are required to withstand dynamic wind uplift according to the requirements in the National Building Code of Canada and tested per the CSA standard A123.21, Standard Test Method for the Dynamic Wind Uplift Resistance of Membrane-Roofing Systems. This requirement has a major impact on the roofing industry, obliging manufacturers to design, test and determine the performance of complete roof assemblies. In addition, this requirement means that each of the other project team members, including designers and installers, must play a pivotal role. As the industry tries to cope with current code requirements, the effects of climate change expose the built environment to more severe environmental stressors. Extreme weather events, including high wind speeds, intense rainstorms, heavy snowfalls, extended heat waves and other stressors, are becoming more frequent and powerful.
With the changing climate and anticipated climate severities, there is a need to further enhance requirements for roof assemblies to resist increased wind load, to control and manage increased precipitation, and to counter increases in temperature from having an impact on durability. To meet this need, NRC, in collaboration with the SIGDERS committee, has developed Performance Requirements for Climate Resilience of Low Slope Membrane Roofing Systems (CSA A123.26), which addresses the severities related to wind and rain.
Evolution of the CSA A123.21
In 1994, the National Research Council of Canada (NRCC) led the way in forming a consortium-based research and development study group, the Special Interest Group for Dynamic Evaluation of Roofing System (SIGDERS), which includes representatives of manufacturers, contractor associations, testing laboratories, homeowners and insurance companies. The group’s research led to the development of the CSA A123.21, Standard Test Method for the Dynamic Wind Uplift Resistance of Membrane-Roofing Systems, which was first published in 2004 and subsequently revised in 2010, 2014 and 2020. Referenced in the National Building Code of Canada (NBCC) since the 2015 edition and adopted by the provincial codes, including the Ontario Building Code (OBC), CSA A123.21 specifies the primary means of assessing a roofing system’s resistance to counteract calculated wind loads and has become a pivotal point in the development of roofing specifications.
Meeting code requirements for wind uplift
To satisfy code requirements for wind uplift resistance, designers must first calculate and/or use the available online calculator to determine the project-specific wind uplift values and include them in the project specifications. In addition, the designer should specify a requirement for the contractor to submit reports issued by third-party testing laboratories to confirm that the procured roof assemblies are rated to exceed the required project-specific wind uplift values. If the designer chooses to include basis-of-design roof assemblies in the specification, the designer may choose to research and/or work with manufacturers to identify rated roof assemblies that meet the project-specific requirements. NRC is developing a portal with database of tested roof assemblies from various manufacturers to provide a centralized resource. At the time of the roof assembly procurement, the roofing contractor can work with manufacturers to identify a roof assembly that is rated to resist the project-specific wind uplift resistance load requirements of all zones at each of the roof areas of the building, and present as a substitution request for designer’s approval.
While selecting a rated roof assembly is an important step, the general contractor and roofing trade must take responsibility for good quality work and the correct installation of the selected system. It is critical to follow the manufacturer’s instructions for the tested assembly, including proper spacing, patterns and installation timing for each component. Materials must be stored properly, and precautions must be taken at the time of installation to ensure the effective functioning of the components.
For the installation of assemblies during winter, those components affected by cold weather conditions, a winter-grade product offered by the manufacturer is to be used. Additionally, crews must pay attention to details at the time of construction, such as temporary seals at perimeter scuppers and openings, and along the end-of-workday assembly terminations, to avoid loss of integrity of the roof assembly due to inclement weather including extreme weather conditions that may occur during installation. Quality control measures by the general contractor and roofing trades are essential to verify that materials and components are properly installed. A general conformance review by the designer and a qualified consultant, as required, is imperative during construction.
Managing precipitation and resistance to water penetration
Addressing the project-specific challenges related to the wind load is a crucial starting point in achieving the long-term durability of roof assemblies, but there are other concerns. The other main challenge is to design roof assemblies that resist and manage precipitation.
Project teams must consider the NBCC requirements for sizing drains and rainwater leaders to address this challenge. In addition, several qualitative measures are followed in the industry that are either industry best practices or standards, including standards published by roofing contractors associations, for example the Roofing Practices Manual of Roofing Contractors Association of British Columbia.
Projected climate severities
With the changing climate and the likelihood of adverse weather conditions, the design and construction of roof assemblies capable of resisting project-specific wind uplift values as required by the building code is a starting point to achieve durable and resilient roof assemblies with long service lives. In addition to meeting current code requirements, designers and contractors also need to understand that further enhancements to how roof assemblies are constructed for long-term durability may be necessary to prepare for climate-change-driven events such as intense windstorms, heavy precipitation and increased temperature. With the Earth’s current surface temperature already reaching 1.5°C warmer than pre-industrial levels, severe climate-related conditions are anticipated immediately and throughout the course of the service lives of existing and to-be-built building stocks. Among building envelope components, roofs tend to be especially vulnerable to climate-related risks due to their exposure to increases and variations in temperature, windstorms causing wind uplift failures and extended water and snow retention.
CSA A123.26-21, a new standard, aims to enhance the resilience of roof assemblies, particularly low-slope membrane roofs, against future climatic conditions by incorporating anticipated wind and rain loads, using data from Climate-RCI, an online tool developed by NRCC, and improving the quality of roofing details. The requirements in the standard, both quantitative and qualitative, are intended to enhance the performance of the roof assemblies and ensure durability by countering future climate severities and reducing wind uplift failures, water ingress issues, safety issues, and maintenance. The standard also provides clearer guidelines for construction practices, which can support designers across regions, provinces and/or jurisdictions.
Designing and testing for optimal performance
Our roof consulting team is at the forefront of understanding and implementing the design and construction of low slope roof assemblies that meet the requirements for wind resistance, waterproofing and other environmental challenges. Our roof testing laboratory in Drummondville, Canada is accredited to perform tests in accordance with CSA A 123.21 and is a member of the UL Data Acceptance Program. EXP’s roofing professionals are actively involved in the SIGDERS committee that spearheads the development of standards and code requirements for low slope roof assemblies. With clients across North America, our experts are equipped to address roofing designs across locations, climates and structural needs.
Learn more about Building Science at EXP.
Adapted from a study that was originally presented at the 2024 IIBEC Building Enclosure Symposium.
Contact the authors:
Bruno Bernard, Project Manager – Roof Testing Laboratory | EXP
Sathya Ramachandran, Architect, OAA, MRAIC, BArch, MASc, Director of Building Science