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What is Window Thermal Performance?

Master Class

How is Window Thermal Performance Regulated and Enforced in Canada?

Thermal Performance and the BC Step Code

Master Class

Last time on the Window Geeks: Master Class, we explored how thermal performance is regulated and enforced in Canada.

The BC Energy Step Code may not specify how to construct a building, but it does identify an energy efficiency target that must be met – while allowing the designer and builder to decide how best to meet it.

After reading this installment, you will...

  • Understand how thermal performance is enforced
  • Understand what BC is doing to adopt these energy standards
  • Understand the U-Values associated with higher and lower efficiency homes

What is the BC Energy Step Code?

Stepped requirements are in place to ensure new homes are built to increasingly efficient standards. These standards have been deemed the BC Step Code. This code encourages builders to work with an Energy Advisor who will model a home virtually and provide guidelines for items such as heat pumps, windows, and insulation. Performance can be offset by wall assemblies and vice versa – meaning it’s all a matter of balance. For example, if high-performance windows are specified, there may be an opportunity to choose lower-performing elements elsewhere. Conversely, if lower-performing windows are specified, the model will likely require substantial wall assemblies to offset the fenestration.

Prescriptive vs. Performance Path

The BC Building Code has multiple compliance paths for windows – one being the prescriptive and the other performance path. The prescriptive method specifies how the building must be constructed and what components are desired for products – like asking for windows to have a certain coating on the glass. The performance method, on the other hand, specifies what standard these components and the building itself should be able to achieve. In our opinion, we prefer the performance path because it is much less rigid and allows for trade-offs in energy performance.

Performance Values

The most common performance values discussed in BC are U-Values and Solar Heat Gain Coefficients. U-Values measure the overall insulating properties of windows and generally become more restrictive as you enter colder climates. SHGCs measure the amount of solar energy (heat) entering the home.

The Energy Step Code, which is part of the building code, allows you to use software to calculate overall home performance and lets you trade off window performance with other elements such as insulation. It is possible when following the performance path that higher U-Value products can be used as long as the performance of other components and assemblies have increased to account for the impact of higher U-Values. The Ministry of Energy created what is called the Energy Efficiency Act to regulate certain products, setting a minimum threshold for performance. This has been superseded by the Energy Efficiency Regulations 2016, an updated version that essentially does the same job. The building code regulates thermal performance at the time of design and permit, while the EER regulates windows at the time of supply. We’ve interpreted that the Energy Efficiency Regulations refer to complying with NFRC standards which are set for standard products. Failing to meet the building code requirements will result in rejected product, while selling/purchasing/importing product that violates the EER can result in a fine and/or jail time. That is because it’s not a code – it is a law.

Note: The EEA is only applicable to Part 9 buildings.

Next time, the Master Class will be bringing you a guide to Code compliance for thermal performance in windows. Sign up and stay tuned!

Written by: Jacquie Vandermeer , March 2, 2023
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