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Multifamily High Performance Envelope

Measure Description

This CASE Report will reduce area-weighted U-factor for the thermal envelope in multifamily buildings and will include the following five submeasures.

Improved Fenestration U-factor and Solar Heat Gain Coefficient

This submeasure will align fenestration U-factor and Solar Heat Gain Coefficient requirements across multifamily buildings based on construction type and whether the fenestration is factory-assembled versus site-assembled. It will also address higher performance fenestration including triple pane windows where feasible.

This measure will include requirements for fenestration efficiency that are categorized by construction type (e.g. wood framed vs metal framed) and/or fenestration assembly method, rather than number of stories, to harmonize multifamily requirements.

Window area limits and metrics (Window to Wall Area Ratio vs Window to Floor Area Ratio)

This submeasure will align window area limits by orientation and total window area across all multifamily buildings. Currently there are separate metrics for low-rise and high-rise residential buildings, resulting in different total window areas and window areas by orientation.

Quality Insulation Installation (QII)

This submeasure will revise quality insulation installation (QII) requirements and inspection protocols for application to multifamily buildings of all types, dependent on construction assembly types.  QII shall be a prescriptive requirement for all multifamily building types, including buildings currently defined as high-rise residential (having four or more habitable stories). An exception for Climate Zone 7, which currently exists for low-rise multifamily buildings, is likely to stay in place and apply to all multifamily buildings.

This measure will include requirements and verification protocols for QII categorized by construction type (e.g. wood framed vs. metal framed, or mapped to construction types used by the fire or structural codes), rather than number of stories, in order to harmonize multifamily requirements. This measure does not propose to change the QII protocol language as it currently applies to low-rise multifamily construction types.

Reduced thermal bridging

This submeasure will mitigate heat transfer through major thermal bridges in a building: wall-roof intersection, wall-floor intersection, wall-fenestration intersection, and wall-exterior projections. The Statewide CASE Team will leverage nonresidential high performance envelope CASE measure on thermal bridging potentially based on ASHRAE 90.1 proposal (addendum AV to 90.1-2016).

The Statewide CASE Team anticipates that the new code will apply one of the following three code compliance implementation methods for this new measure.

  • Adjust assembly u-factor calculation methods to include thermal-bridging elements.
  • Prescribe acceptable details of joints between assemblies or acceptable offsetting insulation for high levels of thermal bridge heat losses.
  • Establish use of UA budgets that include the impact of thermal bridging between assemblies.

Improved wall assemblies

This submeasure will align wall assembly u-factor requirements to be categorized by construction type (e.g. wood framed vs metal framed, or in alignment with construction type labels used by the fire or structural codes), rather than number of stories, to harmonize multifamily requirements. Update wall framing factors and other requirements affecting wall U-factor calculations by construction assembly. This submeasure will address potential conflicts with fire code for exterior wall insulation or dense wall insulations.

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

Submeasure Summaries

Provide Feedback

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.


Give Us Your Feedback

The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

  • Use the form above to provide feedback on this measure.