Reaching for A Passive House Code: California's Nascent Adoption Journey

[Editor’s Note: This article was originally published as part of the 2019 NAPHN Policy Resource Guide, release at its 2019 conference. Registration for this year’s NAPHN conference, PASSIVE HOUSE 2020, opens March 2.]

California’s Building Energy Efficiency Standards, commonly called Title 24, are maintained and updated every three years by two state agencies, the California Energy Commission (CEC) and the Building Standards Commission (BSC). In order for a construction project to receive a permit, it has to show, using approved modeling software, that the total energy consumption of the project does not exceed a consumption baseline defined by Title 24.

In addition to enforcing Title 24, local jurisdictions have the authority to adopt local energy efficiency ordinances, called Reach Codes. These codes exceed the minimum energy efficiency standards. Local jurisdictions must demonstrate that a proposed Reach Code, typically consisting of multiple components, can be implemented cost effectively. The jurisdiction must obtain approval from the CEC and file the ordinance with the BSC for the ordinance to be legally enforceable. A Reach Code can have multiple pathways. It can include its own requirements or require that a project use an established framework such as Passive House, LEED, or other certification.

The California Energy Codes and Standards is a statewide utility program that works in partnership with the CEC, local governments, and other stakeholders to identify Reach Codes tailored to each of California’s sixteen climate zones. Once approved by the CEC, individual jurisdictions can adopt one or more Reach Codes into their local energy efficiency code.

First Steps

In late 2018, Passive House California (PHCA) board members were approached by various city representatives, eager to include Passive House measures or certification in their Reach Codes deliberations, as the California Energy Codes and Standards team commenced their work to develop Reach Code options for the 2019 code cycle. PHCA was encouraged to provide a proposal for inclusion in the scope of the Codes and Standards review. Consequently, the PHCA Board approved a study to compare Passive House buildings to California’s energy code requirements.

To simplify the initial task, PHCA elected to focus on low-rise, multifamily residential buildings using a gas/electric fuel mix. This is currently the most common type of building being permitted in terms of number of units. PHCA’s initial study included only the most heavily populated climate zones—San Francisco, Los Angeles (represented by climate data for Torrance), and Sacramento. Due to this study’s complexity, cost effectiveness was ignored, although it was given consideration when selecting building upgrades.

The Study Comprised Five Distinct Phases:

  1. Procure the official California modeling files for a two-story, multifamily prototype building that complies with the 2019 California residential energy code;

  2. Model that prototype in PHPP;

  3. Modify the building’s characteristics until it qualifies as a certified Passive House;

  4. Modify the original California model to match the Passive House building; and

  5. Determine the effect of the changes on the building’s energy efficiency as per California-defined metrics.

Conversion Challenges

There were some definite challenges to overcome. For example:

  • Rough approximations for separate glazing and window frame components were used because California uses NFRC whole-window specifications,

  • Heating, cooling, and hot water efficiency modifications were excluded so as not to preempt California’s adoption of Federal efficiency standards for that type of equipment,

  • Vicinity shading and thermal bridges were ignored because California modeling software has no way to accommodate those items.

Converting the models from PHPP back to California-approved models revealed the most significant issue: the current approved California modeling software has no provision for modifying multifamily infiltration rates. It assumes that all multifamily buildings leak 7.0 ACH50. Reducing the infiltration rate to 0.6 ACH50 was approximated by converting each multifamily building to a single-family building. An additional sanity check was done by applying the multifamily upgrades to one of the prototype single-family homes. Both are admittedly rough approximations.

Promising Results and Prospects

The results of this initial study show that upgrading low-rise multifamily buildings to Passive House criteria can result in overall energy savings of 13–20% over the 2019 baseline code, a 50% average reduction of heating demand, and a 47%-59% reduction of carbon emissions using PHPP metrics. The single biggest factor contributing to these reductions is the combination of low infiltration rates coupled with a medium-efficiency HRV.

The study, which has been shared with the California Energy Codes and Standards group, makes two strong recommendations: infiltration rates and balanced ventilation equipment should be included in future Reach Code analysis, and infiltration rates should be factored into multifamily and commercial building analysis and modeling software. More importantly, it demonstrates to many jurisdictions and decision makers in California that building to Passive House standards supports the state’s long-term goals of reduced carbon emissions and energy consumption. This, in turn, may lead to the eventual goal of making Passive House certification an alternate pathway to California energy code compliance. In the short-term, parameters showing how to upgrade the California one-story, single-family prototype to Passive House performance have been provided to the Codes and Standards consultant responsible for single-family analysis and recommendations. The consultant anticipates including a formal appendix, specifically discussing Passive House alternatives, to the Reach Codes residential report.

Author: Steve Mann