CSA Group has published CSA Z251, Design of volumetric modular structures, establishing a common technical framework for Canada’s growing modular construction sector, according to Canadian Consulting Engineer. The standard sets new design expectations for how windows, curtain wall assemblies and other glazing components are integrated into factory-built volumetric modules.
What CSA Z251 Covers
According to Canadian Consulting Engineer, the standard addresses structural design, building services, environmental separation, fire protection, manufacturing and architectural considerations. It was developed by a technical committee that included engineers. The standard is intended to complement the National Building Code of Canada by establishing approaches specific to volumetric modular buildings, where modules are manufactured off-site and then assembled on-site.
Why Glazing Contractors Should Pay Attention
For glazing contractors and curtain wall designers, the environmental separation and architectural considerations clauses are the most direct signal. In modular construction, window and curtain wall units are often installed into modules at the factory, then the modules are transported and connected on site. CSA Z251 creates a unified technical framework that sets out how those assemblies need to be designed, detailed and verified as part of the module. The standard does not by itself restate the performance thresholds found in CSA A440 or the North American Fenestration Standard; those remain separate code instruments. Rather, it establishes how glazing elements are treated within the module as a system.
Canadian practitioners will continue to use CSA A440 for window performance and the North American Fenestration Standard for fenestration ratings, while ENERGY STAR Canada handles energy efficiency recognition. CSA Z251 adds a modular-specific layer that coordinates those existing requirements with module design and factory assembly.
Environmental Separation and Building Envelope
For window and curtain wall contractors, environmental separation is the part of the standard that most directly touches their scope. In site-built construction, a glazing assembly is installed after the structural frame and enclosure are complete. In volumetric modular construction, the module's wall, floor and roof assemblies are fabricated in a plant, and windows are typically installed before the module leaves the factory. That reverses the sequence: the glazing assembly must be integrated into the module's air, water, vapour and thermal control layers at the factory, then protected during transport and connected to adjacent modules on site.
Factory Installation and Inspection
Because modules are manufactured off-site and then assembled on-site, as described in the Canadian Consulting Engineer article, quality control for glazing shifts from the field to the factory. Window and curtain wall installations can be completed under controlled conditions, but any rework after modules are joined becomes more difficult. CSA Z251’s inclusion of manufacturing considerations suggests that glazing assemblies will need to be documented, inspected and verified before modules are loaded for delivery.
Coordination with Existing Glazing Standards
CSA Z251 does not replace performance standards such as CSA A440 for windows or the North American Fenestration Standard, and it does not restate ENERGY STAR Canada criteria. Those instruments continue to set the performance targets. What CSA Z251 adds is a modular-specific design layer that tells designers how to integrate those assemblies into factory-built modules and how to demonstrate compliance as part of the overall modular building.
Supply Chain and Procurement
The shift toward factory-built modules also changes procurement timing. Window and curtain wall specifications must be finalized earlier because modules are fabricated on a production schedule. CSA Z251’s manufacturing and architectural considerations point to earlier involvement of fenestration suppliers in design, which can reduce last-minute changes but requires more disciplined specification control.
Market Context and Federal Push
Canada’s modular construction industry is currently valued at more than $5.5 billion and is expected to grow by more than 5% annually through 2029, the Canadian Consulting Engineer article reported. The federal government has identified modular construction as one of the modern methods to support its Build Canada Homes agency.
The publication also noted that governments and industry leads are increasingly looking to modular construction to help accelerate the delivery of housing and other infrastructure, reduce waste, improve worker safety and enable more predictable outcomes.
Industry Reaction
Dwayne Torrey, director of construction and infrastructure standards at CSA, said scaling the sector requires a consistent approach, and that CSA Z251 provides that common framework with clear recommendations and guidance.
Tom Hardiman, executive director of the Modular Building Institute, said standards like CSA Z251 provide the consistency and clarity that give confidence to the companies and communities investing in modular construction.
Relationship to Other CSA Standards
CSA Z251 builds on a broader suite of standards supporting modular construction, including:
- CSA A277, Procedure for certification of prefabricated buildings, modules, and panels
- CSA Z250:21, Process for delivery of volumetric modular buildings
- CSA Z252:23, Volumetric modular construction – Guide to compliance and approval processes
Implications for Modular Glazing Design
For glazing teams, the arrival of CSA Z251 makes it clear that modular projects will demand earlier coordination between module fabricators and fenestration suppliers. The standard’s focus on manufacturing and architectural considerations means window and curtain wall specifications are likely to be locked in before modules leave the factory. The common framework also points to a future in which glazing assemblies are inspected and verified as part of the module, not just on site after installation.
As more provinces and territories adopt volumetric modular approaches, the standard may also influence procurement specifications and municipal permitting. Glazing contractors that understand CSA Z251’s module-level expectations will be better positioned to collaborate with module fabricators and demonstrate compliance early in the design process.