Nonresidential Thermal Bridging

Measure Description

Thermal bridging occurs when conductive elements penetrate a building’s thermal insulation and allow heat to bypass the insulating layer. This reduces the overall effectiveness of the insulation and decreases the efficiency of the building’s thermal envelope by allowing additional heat to escape the building. The current requirements only prescribe U-factors for an assembly (e.g., wall, roof, etc.). These assembly U-factors do not account for thermal bridges that occur at the intersection of two assemblies, such as a wall and a roof. Thermal bridging for poorly designed details at the intersection of assembly can result in overall assembly U-factors that are as much as 50 percent higher than the requirement. Thus, the U-factor requirement for assemblies alone is not enough to capture the impact of thermal bridges because assemblies meeting the requirements may not achieve that level of performance in the field. This submeasure will prescribe detailing of the thermal envelope at major thermal bridges, thereby increasing the efficiency of the envelope and resulting in energy savings. The goal is to mitigate heat transfer through major thermal bridges in a building including wall-roof intersections, wall-intermediate floor intersections, wall-fenestration intersections, and wall-exterior projections, including balconies and overhangs. This submeasure will build upon (though not necessarily replicate) the ASHRAE 90.1 proposal (addendum AV to ASHRAE 90.1-2016).

Submeasure Moved to Future Code Cycles

The Statewide CASE Team investigated code change opportunities for nonresidential thermal bridging for the 2022 code cycle. This measure was considered because of the potential for very significant savings and the energy impacts that are not currently considered in CBECC-Com or Title 24, Part 6. This measure would also potentially harmonize with an addendum being developed by ASHRAE .

After initial research, including interviews with stakeholders, the Statewide CASE Team discontinued pursuing proposed changes for the 2022 code change cycle because there would be no nonresidential registry or third party entity ready to perform field inspection and verification by 2022 nor an established format for professionals to sign off that calculations had been properly performed. Also, the relevant ASHRAE proceedings would not be available in time for the Statewide CASE Team  to leverage them.

To support ongoing research and future code cycle consideration, additional information on nonresidential thermal bridging can be submitted to the Statewide CASE Team through [email protected]. This measure may be pursued through CalGreen (Title 24, Part 11).

Relevant Documents

• Presentation – Oct. 24 – Nonresidential Envelope Part 1: High Performance Envelope Utility-Sponsored Stakeholder Meeting
• Notes – Oct. 24 – Nonresidential Envelope Part 1: High Performance Envelope
• Thermal Bridging Submeasure Summary with Draft Code Language