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Residential High Performance Attics

Residential Envelope

Codes and Standards Enhancement (CASE) Report

The Statewide CASE Team 2019 Title 24, Part 6 Final CASE Report is available below. The Final CASE Report incorporates feedback received during utility-sponsored stakeholder meetings, Energy Commission Pre-Rulemaking workshops, and personal communication with stakeholders. We encourage stakeholders to email feedback on the Final CASE Report to You can also participate in the 2019 Title 24, Part 6 Standards updated by attending the Energy Commission workshops and submitting written comments to the rulemaking docket. Refer to the Pre-Rulemaking and Rulemaking Workshop Notices for instructions on how to submit comments to the Energy Commission’s docket (available here).

Final CASE Report: Residential High Performance Attics

Draft CASE Report: Residential High Performance Attics

Measure Description

The proposed residential high performance attic (HPA) measure increases the prescriptive performance of the residential envelope in certain climates, primarily reducing the cooling season heat transfer through the roof deck, contributing to lower heating, ventilation, and air conditioning (HVAC) loads. The HPA measure as represented in Title 24, Part 6 is based on a traditional ventilated attic with insulation at the ceiling and either ducts fully located in conditioned space or additional insulation added above or below the roof deck. This proposed prescriptive measure only applies to single family and low-rise multifamily buildings in new construction. No changes to the current 2016 HPA prescriptive requirements are being proposed for additions.

In regards to the assumed Standard Design reference case (tile roof with air space between the roof deck and the roofing material) in the performance method, the proposed measure increases the below-deck insulation R-value to:

  • R-19 in Climate Zones 4, and 8 through 16 for single family homes, and
  • R-19 in Climate Zones 4, 8, 9, and 11 through 15 for low-rise multifamily buildings.

This specification represents the proposed prescriptive requirement for the predominant tile roof configuration seen in California production housing. Equivalent performing cases for roofing systems without an air space (typically the case for asphalt roofing materials) and above deck insulation options were also developed and are reported in Section 7.1. Using the performance path, a builder has the full flexibility to choose to follow the prescriptive path, including the proposed 2019 HPA requirements, or trading HPA off against other efficiency measures.

Request for Feedback

The Statewide Utility Team encourages participation in the CASE Report development process through the submission of data—both primary sources and references to existing data. We are requesting data on areas such as energy savings, costs, market impacts, industry practices, barriers to code compliance, etc. from stakeholders. The data will inform the energy savings estimates, cost-effectiveness analysis, compliance and enforcement, and market impacts that will be presented in CASE Reports.

Do you have feedback or data to share? Send us an email at