A Tale of Two Cities: Implications of Envelope Backstops in Recent Energy Codes

Speaker: Stephane Hoffman, PE – Morrison Hershfield

In the drive for increased energy efficiencies, recent energy codes are putting increased focus on the thermal performance of enclosure assemblies. One increasingly popular concept is the introduction of envelope backstops to limit the traditional energy codes approach of accommodating a shortfall in the thermal performance of the enclosure using efficiencies from other building systems. We will contrast the UA restriction approach to envelope backstops adopted in the latest City of Seattle Energy Codes and other US jurisdiction with the TEDI (Thermal Energy Design Intensity) approach adopted by the British Columbia Step Code and other Canadian jurisdictions. We outline the particular challenge this presents for enclosure design of high-rise building using the case study from Artscape project in Vancouver, one of Canada’s tallest Passive House buildings. Examples from the Building Envelope Thermal Bridging Guide will be used to illustrate the current limitations of traditional unitized glazing systems when it comes to accounting for the impact of thermal bridging on enclosure thermal performance. We will conclude with a couple of examples of how manufacturers are adapting the design of unitized glazing system to meet this new challenge.

Codes are putting increased focus on the performance of enclosure. One increasingly popular concept is the introduction of backstops to limit the approach of accommodating a shortfall in the thermal performance of enclosures using efficiencies from other systems. We will contrast the backstops adopted in US and Canadian jurisdictions. We will outline the challenge for high-rise buildings using the case study from one of Canada’s tallest Passive House buildings. Examples from the Building Envelope Thermal Bridging Guide will illustrate the thermal limitations of traditional spandrel design. We will conclude with examples of how manufacturers are adapting to meet this challenge.