Measure Overview
This proposal recommends updates to two issues related to windows in nonresidential buildings: New Construction U-Factors in Climate Zones 1 and 16 for fixed and operable windows and Alteration U-Factors for fixed and operable window replacements.
These proposals do not apply to Glazed Doors or to Storefront, Curtainwall, or Skylight fenestration.
NEW CONSTRUCTION U-FACTORS. Improved U-factors for nonresidential fixed and operable windows in Climate Zones 1 and 16.
ALTERATION U-FACTORS. Updated prescriptive U-factors and RSHGC in Table 141.0-A for alterations, in line with requirements for new construction when certain thresholds are met.
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Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Nonresidential | New construction, additions, alterations | Prescriptive | Update existing feature, add new feature | Update existing verification requirements |
Justification for Proposed Change
NEW CONSTRUCTION U-FACTORS. The last update to Title 24 fenestration U-factors occurred in 2022, when the requirement for fixed fenestration in Climate Zones 9, and 11-15 was changed from 0.36 to 0.34. Prior to this (at least as far back as the 2013 code), the requirement in all climate zones for fixed fenestration has been 0.36 and for operable fenestration has been 0.46.
The International Energy Conservation Code (IECC) proposal CE44-24 for the IECC Commercial code made slight improvements to U-factors for fixed and operable fenestration in IECC Climate Zones 1, and 4 through 8. The changes in IECC Climate Zones 4B (Mixed Dry) and 4C (Mixed Marine) only impact Climate Zones 1 and 16 in California (IECC 4B overlaps CA CZ 16, and IECC 4C overlaps CA CZ 1), leading the Statewide CASE Team to recommend U-factor improvements for fixed and operable windows in Climate Zones 1 and 16. This proposal would maintain code equivalency with the IECC, while cost-effectively maximizing energy savings for Californians.
The existing Title 24 U-factors in CA Climate Zones 2-15 are better than the required fenestration U-factors in the IECC and therefore did not require upgrades.
ALTERATION U-FACTORS. The required U-factors for fenestration alterations have been unchanged since at least the 2013 code. The current requirements are U-0.58 in Climate Zones 3 and 5, and U-0.47 in all other climate zones, applicable to both fixed and operable windows.
The Statewide CASE Team proposes to update these values by requiring that replacement windows (where a certain threshold number of windows are being replaced) comply with the U-factor values for new construction. For fixed windows in California Climate Zones 2-8 and 10, that would be U-0.36; in all other climate zones the requirement would be U-0.34. Similarly, the requirement for operable windows would be U-0.39 in Climate Zone 1, U-0.43 in Climate Zone 16, and U-0.46 in all other climate zones.
IECC proposal CE141-24 provided clarity to the requirements for replacement windows by including a table in the chapter for existing buildings. The proposal was not a technical change; IECC has long required replacement windows to comply with the prescriptive U-factor and SHGC requirements for new construction. At the request of the CEC the Statewide CASE Team evaluated the possibility of using the IECC fenestration replacement requirements but found that their original proposal as noted above would provide significantly more energy savings.
Relevant Documents
Round One Utility-Sponsored Stakeholder Meeting Materials
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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.