California leads the nation in environmental stewardship, and the California Green Building Standards Code—known as CALGreen—stands as a cornerstone of this commitment. For homeowners planning renovations, builders working on new construction, or designers creating Accessory Dwelling Units (ADUs), CALGreen compliance isn’t just required—it’s an investment in sustainable, healthy living spaces.

What is CALGreen?

CALGreen represents Part 11 of the California Building Standards Code, establishing mandatory sustainability benchmarks for both residential and commercial buildings statewide. As the nation’s first comprehensive green building code when adopted in 2010, CALGreen addresses critical environmental challenges through targeted requirements that reduce greenhouse gas emissions, boost energy and water efficiency, improve indoor air quality, and promote responsible resource use.

The code operates on a three-year update cycle as part of Title 24 of the California Code of Regulations (CCR), with periodic interim revisions to address emerging technologies and environmental needs. The current 2022 CALGreen Code became effective January 1, 2023, reflecting the latest advances in sustainable building practices.

Essential CALGreen Requirements for Residential Construction

CALGreen governs new construction projects and substantial renovations, establishing performance standards across multiple building systems. The code’s residential requirements focus on four key areas that directly impact homeowner comfort, operating costs, and environmental footprint.

Water Efficiency and Conservation

Water conservation forms a fundamental pillar of CALGreen compliance. Indoor plumbing fixtures must achieve specified efficiency levels, with toilets limited to 1.28 gallons per flush or less. Outdoor water use receives equal attention through requirements for water-efficient irrigation systems and drought-tolerant landscaping strategies.

Properties with landscape areas exceeding 500 square feet must demonstrate compliance with Water Efficient Landscape Ordinance (WELO) standards, ensuring that outdoor water use remains proportional to actual irrigation needs while supporting healthy plant communities.

Energy and Resource Conservation

CALGreen promotes circular economy principles through strict waste diversion requirements, mandating that builders redirect at least 65% of construction and demolition materials away from landfills. This requirement encourages material recovery, recycling, and responsible disposal practices that reduce environmental impact.

The code also prioritizes building materials with recycled content and restricts volatile organic compound (VOC) emissions from paints, adhesives, sealants, and other finishing materials. These provisions protect both environmental and human health while supporting markets for sustainable building products.

Indoor Air Quality Standards

Recognizing the connection between building design and occupant health, CALGreen establishes comprehensive indoor air quality requirements. Ventilation systems must deliver minimum airflow rates calculated for each specific space, while HVAC equipment requires proper sizing and sealing to ensure optimal performance and energy efficiency.

Material selection requirements mandate low-VOC flooring and finishes, creating healthier indoor environments by minimizing chemical off-gassing that can affect respiratory health and overall well-being.

Environmental Quality Protections

The 2022 CALGreen update introduced enhanced air filtration requirements, including MERV 13 filters for central HVAC systems. These higher-efficiency filters capture smaller particulates, improving indoor air quality in response to increasing concerns about wildfire smoke and urban air pollution.

Moisture control strategies receive detailed attention through requirements for proper flashing installation, drainage plane design, and vapor barrier placement. These measures prevent mold growth, structural damage, and indoor air quality problems that can arise from inadequate moisture management.

CALGreen Compliance for Accessory Dwelling Units

ADUs represent one of California’s most important housing strategies, and CALGreen requirements apply equally to these smaller residential structures. Whether designing a detached unit, attached addition, or garage conversion, ADU projects must meet the same environmental performance standards as primary residences.

New ADU Construction Requirements

Newly constructed ADUs must satisfy all mandatory CALGreen provisions applicable to low-rise residential buildings. This includes water efficiency standards, waste diversion requirements, indoor air quality measures, and energy conservation provisions. The compact nature of most ADUs can actually make some requirements easier to achieve, as smaller spaces often require less complex mechanical systems and generate less construction waste.

Conversion Project Considerations

Converting existing spaces like garages or basements into ADUs may involve more limited CALGreen applicability, depending on the renovation scope. However, common upgrades such as energy-efficient lighting, high-performance plumbing fixtures, and indoor air quality improvements typically remain required regardless of the existing structure’s age or condition.

Site Development Requirements

Detached ADUs and substantial site modifications may trigger additional CALGreen provisions related to stormwater management and pervious paving systems. These requirements help manage runoff, reduce flood risk, and support groundwater recharge—particularly important considerations as California addresses ongoing drought conditions and climate change impacts.

Understanding CALGreen’s Tiered Structure

CALGreen employs a tiered approach that balances statewide consistency with local flexibility. The mandatory provisions apply universally across California, establishing baseline sustainability performance for all covered projects. However, local jurisdictions can adopt Tier 1 or Tier 2 voluntary measures to achieve more aggressive environmental goals.

These voluntary tiers allow progressive communities to push beyond minimum requirements, creating regional leadership in sustainable development while maintaining market flexibility. Before beginning any project, confirm with your local building department whether enhanced tier requirements apply in your jurisdiction.

Ensuring Compliance and Documentation

CALGreen compliance requires careful coordination between project teams and building officials throughout the design and construction process. Most residential projects, including ADUs, must submit completed CALGreen checklists or worksheets during the permitting phase, demonstrating how proposed designs will meet applicable requirements.

Construction phase compliance often involves on-site verification by building inspectors or qualified third-party raters, particularly for complex systems like HVAC installations that require Home Energy Rating System (HERS) testing. Early coordination with inspectors and clear documentation practices help ensure smooth approval processes and successful project completion.

Building California’s Sustainable Future

CALGreen compliance represents more than regulatory obligation—it embodies California’s commitment to environmental leadership and climate resilience. Whether designing a new home or creating an ADU, these requirements guide development toward buildings that operate more efficiently, provide healthier living environments, and minimize environmental impact.

As resource constraints intensify and climate challenges grow more urgent, CALGreen offers a proven framework for responsible development. By embracing these standards, builders and homeowners contribute to a more sustainable built environment while creating spaces that deliver lasting value through reduced operating costs, improved comfort, and enhanced durability.

The path to sustainability runs through thoughtful building design, and CALGreen provides the roadmap for success.