The California Energy Commission is responsible for ensuring new and existing buildings improve energy efficiency and indoor environmental quality. Title 24, Part 6 covers the specific details regarding all low-rise residential buildings including single-family home new construction, which is the focus of the report. Local agencies enforce and verify compliance to the codes.

Codes are updated every three years to incorporate new technologies and construction techniques that are cost-effective for a homeowner over the expected lifespan (30 years) of the home. Each iteration of the code is designed to save energy, improve indoor comfort and air quality, reduce the need for additional power plants, and reduce greenhouse gases. The code details are specific to the sixteen climate zones in the state.

The 2019 standards went into effect on January 1, 2020. The California Energy Commission estimates the standards will add about $40 to an average monthly 30-year mortgage payment but will save consumers $80 per month on heating, cooling and lighting bills.

Local governments are allowed to have more stringent standards than state codes. However, to implement, the local municipalities must prove their standards will save more energy cost-effectively.

2019 Title 24 Building Standards

The California Energy Commission estimated the 2019 Title 24 building standards would reduce annual electricity usage by 653 gigawatt-hours and natural gas consumption by 9.8 million therms. Its reported that in 2020, these standards were expected to affect 117,000 new single-family homes in the state.

Recently adopted, the new residential standards' primary focus is on updated ventilation requirements and smart residential solar PV systems. Many of the changes attempt to align details with nationally accepted standards or to prescribe requirements for higher efficiency products or installation methods for categories such as solar PV, ventilation, insulation, and lighting.[1]

Mandatory, Prescriptive, and Performance

Building standards can dramatically impact home energy use and are a key element of how California has kept consumption flat. While the standards cover hundreds of details, there are three main categories: mandatory features, prescriptive requirements, and performance options. All parts of the codes are evaluated for cost-effectiveness.  

• Mandatory features apply to every home built and their associated costs are applicable to the base home. As described, they are not optional.
• Prescriptive requirements often vary by climate zone, but are specific in how they address a building component. For example, the type and amount of insulation is different by climate zone but still required. These prescriptive standards are proven cost-effective measures for a minimum energy savings via construction techniques or a technology solution. Following the prescriptive requirements is often easier for the builder or trades involved as they essentially follow a set of instructions, but this method offers less flexibility. Unlike mandatory items, there can be more than one choice and either can be chosen as an acceptable solution. 
• Performance options exist to give builders flexibility and encourage new solutions. Builders can submit alternative design choices for prescriptive requirements. If the building achieves the same overall efficiency as using the prescriptive option, it is likely to be approved and then the performance option may be used.

Each of the construction methods or technologies are measured against the base home by climate zone from the previous standard. For example, the cost to build a home to the 2019 standard is compared with cost to build to the 2016 code, and then the energy savings are included in the evaluation. For example, the 2016 code resulted in an increase of $2,700 to construct the home and saves $7,400 in energy and maintenance costs over 30 years. This translates to an $11 per month increase on a 30-year mortgage with a 5% interest rate. Energy and maintenance savings add up to $31 per month. The net gain to the homeowner was $20 per month.

The entire structure must meet a minimum building efficiency. In the state of California, this is called the home’s energy budget, which is the energy consumption per square foot of floor space. Before construction begins, the home’s design must be modeled through state-approved software. One of the software options is CBECC-Res, a free computer program developed by the California Energy Commission for use in demonstrating compliance with the California Residential Building Energy Efficiency Standards.