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A Guide to ADU Solar Requirements in California
Workplace Inspiration

A Guide to ADU Solar Requirements in California

|Dec 15, 2023

The sun not only graces the skies but also plays a pivotal role in shaping the way homes are designed and powered in the vast canvas of California living. From the sleek simplicity of prefab ADUs to the sturdy charm of manufactured homes in California, Californians are weaving sustainability into the very fabric of their living spaces. Join us on a journey where we not only unravel the solar secrets behind these housing marvels but also decipher the nuances of California ADU law, illuminating the path towards a brighter and more eco-conscious future.

Navigating the Solar Mandate for New ADUs in California

California has implemented a mandate requiring newly constructed, non-manufactured, detached accessory dwelling units (ADUs) to install solar panels. This requirement applies to ADUs of all sizes, regardless of whether they are built on the same lot as an existing single-family home or on a separate parcel of land.

The purpose of this mandate is to encourage the adoption of solar energy for these secondary housing units, thereby reducing their reliance on conventional electricity sources and promoting a more sustainable approach to housing development. The specific solar capacity required for an ADU depends on several factors, including the size and location of the unit, as well as its projected electrical usage.

Navigating the Solar Mandate for New ADUs in California

Determining Solar Capacity Requirements for ADUs

To determine the minimum solar capacity required for an ADU, a formula is used that takes into account the unit's conditioned floor area (CFA), its climate zone, the number of dwelling units in the structure, and the type of dwelling unit. The formula is as follows:

kW (PV)required = (CFA x A)/1000 + (NDwell x B)


  • CFA is the conditioned floor area of the ADU in square feet
  • A is a factor that varies depending on the climate zone of the ADU
  • NDwell is the number of dwelling units in the structure
  • B is a factor that varies depending on the type of dwelling unit

By using this formula, local authorities can determine the appropriate solar capacity for each ADU project, ensuring that the unit generates enough solar power to offset a significant portion of its electricity consumption.

Determining Solar Capacity Requirements for ADUs

Exemptions to the Solar Mandate

While the solar mandate applies to a broad range of ADU projects, certain exceptions may apply under specific conditions. These exemptions include:

  • Manufactured ADUs: Prefabricated ADUs, also known as manufactured homes, are exempt from the California solar requirement. This is because a different set of standards regulates manufactured homes than site-built ADUs.
  • ADU additions and conversions: If you are adding an ADU to an existing single-family home or converting an existing structure into an ADU, you are not required to install solar panels. However, if the ADU is being built as a completely new structure, the ADU solar requirement in California applies.
  • Small ADUs: ADUs that are less than 800 square feet in size may be exempt from the solar requirement if they meet certain shading restrictions. This exemption is based on the assumption that smaller ADUs are less likely to have sufficient roof space for solar panels.

Exemptions to the Solar Mandate

Benefits of Installing Solar Panels on ADUs

Installing solar panels on your ADU offers several advantages:

  • Reduced electricity bills: Solar panels can significantly lower or even eliminate your ADU's electricity bills, saving you money in the long run.
  • Increased property value: Studies show that ADUs with solar panels tend to have higher resale values than those without solar panels.
  • Reduced environmental impact: Solar power is a clean and renewable energy source that helps reduce greenhouse gas emissions and contributes to a more sustainable future.

By installing solar panels on your ADU, you can enjoy these significant benefits while also contributing to a more sustainable future.

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Considerations for ADU Solar Installation

Before embarking on an ADU solar installation project, it is important to consider several factors to ensure a successful and cost-effective implementation:

  • Cost: The upfront cost of solar panel installation can be significant, but the long-term savings on electricity bills and the potential increase in property value often offset the initial investment.
  • Roof Suitability: Your ADU's roof should be large enough and have the correct orientation to accommodate solar panels.
  • Permits: You may need to obtain permits from your local government before installing solar panels.
  • Professional Help: It is advisable to consult with experienced solar installers to determine the specific requirements for your ADU project and to choose the most suitable solar panels.

By carefully considering these factors, you can make an informed decision about whether or not to install solar panels on your ADU and ensure that the installation process is smooth and successful.

Considerations for ADU Solar Installation


1. What are the California solar requirements for new homes?

In line with California's commitment to sustainable living, new homes in the state are required to adhere to specific solar standards. This initiative aims to integrate renewable energy sources, contributing to a greener and more energy-efficient future.

2. How does California solar requirement impact new construction?

California's solar mandate for new construction extends beyond traditional homes. Whether it's the sleek lines of prefab homes or the innovative designs of container homes in California, the requirement ensures that every new dwelling embraces solar technology, fostering a harmonious blend of modern living and eco-conscious practices. California solar requirement for new construction is pretty lax so there is nothing that you have to worry about.

3. Are prefab homes in California subject to solar requirements?

Absolutely. Prefab homes in California, with their efficient construction methods, are an integral part of the state's housing landscape. Embracing solar requirements, these homes not only showcase contemporary design but also contribute to the state's renewable energy goals.

4. How about container homes in California? Are they exempt from solar mandates?

No exemptions here. A container home in California, known for its uniqueness and adaptability, must align with California's solar mandates. The challenge lies in creatively integrating solar solutions into these structures, showcasing the state's commitment to innovation and sustainability.


Whether you're contemplating the simplicity of prefab homes in California, the uniqueness of container dwellings, or the versatility of prefab ADU in California, California's solar requirements are the common thread weaving through the state's commitment to sustainable living. As new homes rise, embracing solar technology in their construction, California stands as a beacon for the nation, illuminating the path towards a future where every home is a testament to eco-conscious living.

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