New solar heat gain coefficient limits in the 2025 National Building Code of Canada create three distinct compliance paths — and shrink the pool of qualifying fenestration products. Here's what manufacturers, architects, and glazing contractors need to know before spec sheets land.
A Code Update That Changes the Glass Package Math
At the Fenestration & Glazing Industry Alliance (FGIA) Fall Conference, a panel of Canadian codes experts walked attendees through what may be the most consequential change to Canadian residential fenestration specifications in a decade: new solar heat gain coefficient (SHGCt) limits embedded in the 2025 National Building Code (NBC) of Canada.
Moderated by Amy Roberts, FGIA's Director of Canadian Codes and Advocacy, the session featured leaders including Jeff Baker (WESTLab Canada), Lisa Bergeron (JELD-WEN) and Paul Bush (Vitro Architectural Glass), who mapped out the critical new compliance path options manufacturers and builders must adopt to meet these strict energy mandates.
The headline takeaway for specifiers: SHGC is no longer a secondary metric behind U-factor. It's now a gating criterion — and one that will shrink the roster of products that can legally hit a project.
Three Paths, One Tighter Envelope
According to Baker, the NBC introduced new changes in 2025, and there are now three paths to compliance in the code. He described them as follows:
- A performance path in which builders work with an energy advisor and are free to use any fenestration product, provided the whole building meets its performance target
- A prescriptive path in which you can score points to achieve NBC tiers 1-5 by using components that are above minimum code in each climate zone
- A new prescriptive path in which there is a set of prescriptive components that comply by climate zone
Critically, in both prescriptive paths, SHGC limits will apply. That single sentence is why product managers at every Canadian window and IGU fabricator are rebuilding their spec matrices this fall.
Why the Code Is Getting Stricter About Solar Gain
The motivation isn't just carbon. It's occupant comfort in envelopes that have gotten dramatically better at trapping heat. Baker said, 'We will see how these changes go in terms of SHGC and U-factor,' noting that the code was asked to address this in highly efficient building envelopes to address overheating.
That's a familiar problem for anyone who has designed a well-insulated home in a cold climate: once you push U-factors low and airtightness high, uncontrolled solar gain can turn a south-facing bedroom into a sunroom in shoulder seasons. The 2025 NBC is codifying that lesson.
The Product Squeeze Is Real
The panel didn't sugarcoat the implications for manufacturers. Bush noted that these changes reduced the number of products that can comply with the code.
For glass fabricators and window OEMs, that reduction cuts several ways:
- Low-e coating selection tightens. Coatings tuned for high SHGC (favored historically in cold Canadian climates to harvest passive solar) may no longer clear prescriptive thresholds in the new paths.
- Frame design matters more. The discussion examined the practical implications for manufacturers, including considerations for frame design, product testing, certification and regional market variations.
- Triple-glazed IGUs become a specification pivot point for hitting both U-factor and SHGC ceilings simultaneously.
- Regional SKUs multiply. A window that qualifies in one climate zone may not qualify in another under the new prescriptive path.
What Architects and GCs Should Do Now
For design and construction teams working on Canadian projects — or U.S. teams with cross-border portfolios — the near-term action items are concrete:
- Ask fenestration suppliers which NBC compliance path their submittal packages target. The performance path preserves product flexibility; the prescriptive paths narrow it sharply.
- Re-verify SHGC on any product carried over from a pre-2025 specification. A window that met code last year may not meet code this year, even if U-factor is unchanged.
- Coordinate early with the energy advisor if you're pursuing the performance path. Whole-building modeling gives you room to specify glass optimized for daylight and view — but only if the modeling is done before submittals are locked.
- Watch how ER (Energy Rating) interacts with the new limits. Panelists shared insight into key performance metrics, including the relationship between solar heat gain coefficient (SHGC), U-factor and Energy Rating (ER), and how these factors influence glass package selection and overall product functionality.
The Bigger Picture
The 2025 NBC changes sit alongside a broader Canadian push toward net-zero-ready housing by 2030 and evolving ENERGY STAR Canada specifications. For manufacturers, the message from Ottawa is consistent: high-performance envelopes are now the floor, not the ceiling. For architects and contractors, the message is equally clear — SHGC needs to be treated as a first-order design variable, not a footnote on the window schedule.