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June 15, 2016 - 3 min

How To Design a CSA A123.21 Roofing System in 3 Steps

Published by SOPREMA

Three main steps are required to design a CSA A123.21 roofing system. This article summarizes these steps, in addition to centralizing all resources needed to be able to determine the roofing system that best matches the parameters of your project.

1. Determine the Wind Load of the Designed Building

SIGDERS developed an online calculator called Wind-RCI which is based on data and comments booklet from Part 4 of the National Building Code of Canada.

To perform a Wind-RCI calculation, you will need to determine:

  1. Location of the building in Canada ;
  2. Building dimensions ;
  3. Building exposure ;
  4. Building openings ;
  5. Building importance .


Wind-RCI calculated the specified wind loads for various zones (i.e., field, edge and corner) of the roof assembly in accordance to the building code.

2. Find the CSA A123.21 Roofing System That Meets the Project's Parameters

SOPREMA currently has more than 80 assemblies of all types, including adhered and partially adhered roofing systems as well as systems with mechanically fixed membranes.

3. Apply a Minimum Safety Factor of 1.5

System rating obtained from the CSA A123.21 testing should be higher than the specified wind load when a minimum safety factor of 1.5 is used.

You can find a complete list of CSA A123.21 certified roofing systems available in the market on the exp website from the dropdown list Shown manufacturers, as illustrated below.

Exp reports should allow you to choose roofing systems and related components with resistance data higher than the load data. 


Designing roof assembly according to Ultimate Limit States (ULS) requires multiplication of 1.4 (principal wind load effect factor) to the specified wind loads for various zones (Table – Division B – National Building Code of Canada -2010).