Multifamily Envelope

Proposal Description

This CASE Report will focus on three measures that are grouped into the ‘Envelope’ category of building systems. These three measures work in conjunction to reduce the total amount of heat transfer that occurs in a building from the conditioned inside air to the outside ambient air.

Data may be provided anonymously. To participate or provide information, please email Avani Goyal ([email protected]) directly and CC [email protected].

• Cool Roof Improvements
• Improved Wall Performance
• High Performance Windows

Cool Roof Improvements

This measure would increase aged solar reflectance (ASR), thermal emittance (TE) and solar reflectance index (SRI) value requirements and expand cool roof requirements to more climate zones. Cool roofs reduce the heat absorption into the roof materials, reducing the cooling loads in the building. The proposed code changes intend to align more closely with the 2022 Title 24 nonresidential or single family residential cool roof requirements.

For steep-sloped roofs, Option B, the proposed changes would increase the requirement for Climate Zones 10,11,13 and 15 from an ASR of 0.20 to 0.25 and a TE of 0.75 to 0.8.

For low-sloped roofs, Option D, the current prescriptive code for roof requires multifamily low-sloped roofs have a minimum ASR of 0.63, a TE of 0.75, and an SRI of 75 in Climate Zones 9 through11 and 13 through15. Proposed code changes would expand these requirements to other Climate Zones 2, 4, 6 through 8, and 12

Data Needs/Stakeholder Information Requests

• Technical Feasibility – Information from manufacturers and specifiers on the following topics:
  1. Specifiers – Does available (stocked) product selection drive specifications? Are higher SRI and emissivity products available through special order and is that path chosen as a tradeoff in the performance method?
  2. Manufacturers – Are there limitations to the range of SRI than can be introduced while still maintaining the range of esthetic options desired for architectural purposes? What are the most specified roof colors and are there higher SRI versions that may be considered visually equivalent for architectural purposes?
• Market Readiness – Information from manufacturers on product availability and any barriers to increasing the SRI requirements for cool roofs.
  1. Manufacturers – Availability of cool roof products in the California market that exceed the current code for SRI and thermal emissivity. Are there any barriers to introducing higher performance cool roof products into the CA market? Do municipalities limit the SRI to address glare in a manner that will cause conflict between the Code and local ordinance?
• Costs – Information from manufacturers on the cost of cool roof products.
  1. Manufacturers – What are the cost implications of increasing the SRI of roofing products? Is there a premium to specifying a cool roof with asphalt shingles compared to a non-CR rated product? Does this cost difference increase as the SRI increases?

Improved Wall Performance

High performance window measure will save energy by reducing the amount of heating or cooling needed to keep the indoor air temperature in the desired comfort range. This measure would improve prescriptive U-factor and solar heat gain coefficient (SHGC) for all categories of multifamily fenestration, including curtainwall, architectural windows, and punched windows. The Team proposes reduction of prescriptive U-factor requirement for All Other window category from 0.3 to 0.28 in climate zones 1,3-5, 11 and 13-16 and modifying prescriptive minimum RSHGC requirements of multifamily buildings with four or more habitable stories to be “NR”, no RSHGC requirement, in heating dominated climate zones 1,3,5 and 16 across all window type categories. The standard design will assume 0.35 RSHGC in performance approach.

This measure is aligned with changes to the single-family residential requirements. The proposed changes in prescriptive requirements are extended to additions and alterations scenarios as well.

Data Needs/Stakeholder Information Requests

• Technical Feasibility – Information from manufacturers and specifiers on the following topics:
  1. Specifiers – Are higher (above code minimum of R-13 and R-20) R-value insulation products used in wall cross-sections as a tradeoff in the performance method? What do most projects have for insulation in typical wall cross-sections?
  2. Manufacturers – Are there limitations to the range of R-value than can be accommodated in 2×4 and 2×6 wall cross-sections? What is the practical limit for R-value in these walls based on space available or other limitations?
• Market Readiness – Information from manufacturers on product availability and any barriers to increasing the minimum R-value requirements for walls.
  1. Manufacturers – Are R-value 15 and 21 insulation products readily available in the market for specification?
• Costs – Information from manufacturers on the cost of insulation products.
  1. Manufacturers – What are the cost implications of increasing the minimum R-value from 13 to 15 in 2×4 walls, and from 20 to 21 in 2×6 walls?

High Performance Windows

This measure would improve prescriptive U-factor and solar heat gain coefficient (SHGC) for all categories of multifamily fenestration, including curtainwall, architectural windows, and skylights. This will save energy by reducing the amount of heating or cooling needed to keep the indoor air temperature in the desired comfort range.

However, because of complex interactions associated with thermal lag between the building and the outside air, improving (lowering) the U-Factor value will not necessarily reduce the annual building energy consumption. There are conditions where the lower U-Factor might improve annual heating energy but worsen the annual cooling energy to the point where the total energy consumption will increase. The Statewide CASE Team will evaluate this as part of the measure development process. This measure will also be coordinated with changes to the residential and nonresidential fenestration requirements.

Data Needs/Stakeholder Information Requests

• Technical Feasibility – Information from manufacturers and specifiers on the following topics related to high performance windows:
  1. Specifiers – Preferences for window specifications; are higher performance windows used in performance metho compliance approaches? What product types are used when specifying higher performance? Do triple pane or thin triples get specified? Are there any practical reasons (other than cost) that higher performance windows aren’t chosen at times?
  2. Manufacturers – Are there any reliability or other limitations to window units that make high performance windows less reliable or have lower life expectations?
• Market Readiness – Information from manufacturers on product availability and any barriers to introduction for high performance windows.
  1. Manufacturers – Availability of window products in the California market that exceed the current code for U-factor. Are triple pane or thin triple window units available? Are there any barriers to introducing higher performance windows into the CA market? Are higher performing products available in traditional double pane configurations that can compete with triple or thin triples?
• Costs – Information from manufacturers and distributors on the cost of high performing windows.
  1. Manufacturers – Are better than code windows sold at a rate (currently) to support standard production lines and distribution? What are the cost implications of improving a window unit from the current code performance level up by a U-factor of 0.02? Does this increase extend linearly for each 0.02 beyond code?
  2. Distributors – Are specifiers driving the selection of window performance by requesting (specifying) improved performance, or do specifiers allow product availability and/or cost determine specifications?

Data may be provided anonymously. To participate or provide information, please email Avani Goyal ([email protected]) directly and CC [email protected].