Nonresidential Envelope

Proposal Description

This proposal presents three cost-effective code changes that would improve the envelope performance in nonresidential buildings: opaque assemblies, vestibules, and windows. The CASE Report linked below contains pertinent information supporting the measures.

Opaque Assemblies

The opaque assemblies of the building envelope are all those that are not transparent. This proposal would make the prescriptive U-factors more stringent for new wall and roof/ceiling assemblies, by climate zone. All assemblies would be affected except metal-framed walls, for which the U-factors were revised during the 2022 Title 24, Part 6 code cycle. This proposal would not apply to alterations. It would not add or modify field verification or acceptance tests or require any technology not previously regulated.

Vestibules

The proposed code change would establish a new mandatory requirement for vestibules in nonresidential buildings with high-traffic main entrances. The affected building types would be assembly, business, education, institutional, and mercantile. The vestibule requirement would be applicable to main entrances in new construction and additions. It would not apply to alterations. Exceptions to the requirement would parallel those identified in ASHRAE 90.1 and in IECC, including the option of using a revolving door or air curtain in some applications.

Windows

This proposal would set a new mandatory requirement establishing U-factor values for vertical fenestration assemblies for alterations, additions, and new construction. The proposed mandatory requirements would apply to all vertical fenestration including fixed windows, curtainwall or storefront, and operable windows.

Currently, Title 24, Part 6 includes prescriptive U-factor and RSHGC requirements for exterior vertical fenestration, but these values can be traded away for higher efficiency HVAC equipment or other building systems when a designer uses the performance path to achieve code compliance. This measure, by establishing maximum mandatory U-factor for vertical fenestration, would ensure that there is a minimum level of window efficiency that cannot be replaced by a non-envelope system that typically has a much shorter lifespan.