Wind-RCI: Calculating Wind Uplift Resistance of Roofs in Accordance with the CSA A123.21 Standard

Since 2015, the CSA A123.21 standard has been the only standard for determining the wind uplift resistance of roofing systems. In a context of increasingly frequent extreme weather events, designing roofs capable of resisting wind loads is a priority for ensuring the sustainability of buildings.

This standard provides a rigorous framework for testing and evaluating the performance of roofing systems subjected to dynamic wind loads. It thus ensures compliance with the safety and performance requirements established by the National Building Code of Canada (NBCC).

Calculating wind loads is a crucial step in the design of roofing systems. To assist in this process, the Wind-Roof Calculator on the Internet (Wind-RCI) tool was developed by the Special Interest Group for the Dynamic Evaluation of Roofing Systems (SIGDERS). This online tool allows building professionals to estimate wind loads in full compliance with the National Building Code of Canada.

The calculator is used to meet Canadian standards, avoid human error, ensure safety, and facilitate design.

To use Wind-RCI, you will need to determine the following:

• The location of the building in Canada
• The dimensions of the building
• The exposure of the building
• The opening of the building
• The risk category of the building

The tool will then provide wind loads for different areas of the roof (centre, edges, and corners) in accordance with the requirements of the National Building Code.

SOPREMA Canada offers a wide selection of assemblies that are evaluated according to the CSA A123.21 standard. These assemblies undergo rigorous laboratory tests that simulate dynamic wind loads in order to evaluate the resistance of the roof to these loads. The test results are presented in the documentation available on our website. Our evaluated solutions help optimize roof design and ensure compliance with current standards.

The roofing systems that comply with the CSA A123.21 standard include the following:

• Mechanically attached roofing systems (MARS) in which the waterproofing membrane is mechanically attached to the deck with fasteners.
• Adhesive-applied roofing systems (AARS) in which all components are bonded.
• Partially attached roofing systems (PARS) in which the membrane is adhered and at least one component below the membrane is mechanically attached.

The SOPREMA test results presented in the documentation include a weighting factor, in accordance with the requirements of the CNBC. Depending on the requirements, this weighting may be referred to as a “safety factor” or as a “resistance factor.”

This means that roofing systems must bear a greater load during testing than the calculated load. This weighted resistance compensates for the following factors:

• Uncertainties related to wind loads
• Potential calculations errors
• Material wear

Professionals can also refer to the summary of CSA A123.21-tested assemblies, a comprehensive reference for selecting an optimal roofing system.

By complying with the CSA A123.21 standard and the requirements of the National Building Code, roof design can effectively address the challenges of wind loads. The Wind-RCI tool facilitates the calculation of these loads, thus ensuring building compliance and safety.

Thanks to SOPREMA laboratory tests, professionals have access to reliable solutions, which include mechanically attached, adhesive-applied and partially attached roofing systems. To find out more, visit the documentation pages or contact one of our experts.