ASHRAE Journal - June 2023 - 42

TECHNICAL FEATURE
Thermal Bridging
Requirements in
Standard 90.1-2022
BY LEN SCIARRA, AIA, MEMBER ASHRAE; RAHUL ATHALYE; JONATHAN HUMBLE, FAIA, MEMBER ASHRAE; CHRIS MATHIS, FELLOW/LIFE MEMBER ASHRAE; BEN MEYER; MIKE TILLOU, P.E.,
MEMBER ASHRAE; ROBERT ZABCIK, P.E., ASSOCIATE MEMBER ASHRAE
ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Sites and Buildings Except Low-Rise
Residential Buildings, offers " the minimum energy efficiency requirements for design
and construction of new sites and buildings and their systems, new portions of buildings
and their systems, and new systems and equipment in existing buildings, as well
as criteria for determining compliance with these requirements. " The 2022 edition of
Standard 90.1 incorporates many changes to the building envelope, lighting, mechanical,
service hot water, and renewable energy systems that span the prescriptive and
performance compliance paths. These changes will be described in a series of articles
in ASHRAE Journal. This article, the second in the series, focuses on changes in Section
5, Building Envelope, related to thermal bridging in building envelopes.
For simplicity and in support of the energy modeling
programs then available in Standard 90.1, the building
envelope was broken into two main categories: (1)
opaque (walls) and (2) fenestration (windows). The
opaque envelope was represented by an overall assembly
U-factor that was then translated into an R-value of
insulation for ease of compliance.
This overall U-factor was then used for modeling
and assumed a perfect connection to other building
elements. As wall insulation levels were increased in
subsequent Standard 90.1 editions, a disparity grew
between how buildings are constructed and the ideal
thermal models used for compliance. This disparity led
to requests for a more rigorous approach to modeling
and calculating the effects of real-world building assemblies
on ideal (modeled) U-factors. Therefore, several
research projects studied the effects of thermal bridging
in building envelopes.1,2,3
The new provisions for thermal bridging mitigation
address common assembly interfaces, such as floor-toroof
and floor-to-wall connections. Whether projects
use the prescriptive, trade-off, or modeling compliance
path, Standard 90.1 provides guidance and default
values for steel-framed, mass, and wood-framed walls
and roofs. However, not all thermal bridges in every
building were addressed in the new provisions; the
focus was regulating the most common intersections
and scenarios.
Organization of New Thermal Bridges Content
The thermal bridging provisions introduced into
Standard 90.1-2022 are in Section 5.5, which means
Len Sciarra, AIA, is architect/technical director, Farr Associates, Chicago. Rahul Athalye is program director, codes and standards, NORESCO, Davis, Calif. Jonathan Humble, FAIA,
is regional director, American Iron and Steel Institute, West Hartford, Conn. Chris Mathis is president, MC2 Mathis Consulting Company, Asheville, N.C. Ben Meyer is building enclosure
business director, Siplast, Moseley, Va. Mike Tillou, P.E., is mechanical engineer, Pacific Northwest National Laboratory, Buffalo, N.Y. Robert Zabcik, P.E., is president, Z-tech
Consulting, Katy, Texas.
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