In 2020, California became the first state to require new homes to be equipped with solar panels to offset the use of grid electricity as part of its goal to achieve net-zero emissions by 2045. Known as the California Solar Mandate or Title 24, this standard applies to single-family homes, apartments, condos, and Accessory Dwelling Units (ADUs).

ADUs are small, fully-finished living spaces that can be rented out or used as additional living space. They are also known as in-law suites, granny flats, and casitas. For the most part, new ADUs need to have solar panels to be in compliance with California Title 24 Building and Energy Efficiency Standards. But, read on, there are exceptions.

According to the California Department of Housing and Community Development (HCD) 2020 ADU handbook, “…newly constructed ADUs are subject to the Energy Code requirement to provide solar panels if the unit(s) is a newly constructed, non-manufactured, detached ADU.”

Solar panels are required to offset the ADUs electricity consumption, but they do not necessarily need to be installed on the ADU. They can also be installed on the main house, ground, other eligible structures, added to an existing on-site arrays or, in some cases, to community solar arrays.

It’s important to note that these standards only apply to ADUs for which permitting was submitted after January 1, 2020. So, although it might be worth it for the energy savings and additional home value, if you had or built an ADU prior to 2020 you don’t need to add solar panels for it.

ADU Solar Exemptions
Now, you may have noticed in the Title 24 ADU requirements above that HCD specifically requires solar panels for “newly constructed, non-manufactured, detached ADU(s).” That leaves room for exemptions for the solar requirement for some ADU projects.

Specifically, HCD’s 2020 ADU handbook states, “ADUs that are constructed within existing space, or as an addition to existing homes, including detached additions where an existing detached building is converted from non-residential to residential space, are not subject to the Energy Code requirement to provide solar panels.” Here are some scenarios that could qualify for an exemption from Title 24.

If you are adding to or converting an existing structure to create your ADU, you may be exempt from Title 24 solar requirements. That’s because additions and conversions can be permitted as alterations instead of new construction. And, as the HCD pointed out, addition and conversion projects are not subject to the solar panel requirements in the energy code.

Exempt additions or conversions may include:
• Converting a detached garage to an ADU
• Converting part of your primary home to ADU
• Constructing an ADU as an addition to your primary home

Now, there are some gray areas here. For example, if you completely tear down a detached garage and rebuild it as an ADU, is that a conversion or new construction? The answer will likely require a discussion with your city planning department, and it may be worth considering early on whether to risk delaying your ADU project in order to skirt around solar panel requirements.

Is Your ADU a Manufactured Unit?
Manufactured ADUs are also exempt from Title 24 solar requirements. Just like manufactured homes, manufactured ADUs are built off-site, transported, and placed on a foundation on-site. Manufactured ADUs are regulated by differently than site-build ADUs and are exempt from solar panel requirements in California.

Manufactured ADUs may include tiny homes, modular homes, and other structures built primarily offsite. However, it’s worth consulting your city planners ahead of time to fully understand what qualifies as a manufactured ADU.

Does the ADU Have a Too-small or Shaded Roof?
Another avenue for Title 24 exemptions is for particularly small or shaded roofs. Even as the biggest advocates of rooftop solar, we’ll be the first to tell you solar panels and shade don’t mix.

According to a 2020 newsletter from the CEC, “no PV is required if the effective annual solar access is restricted to less than 80 contiguous square feet by shading from existing permanent natural or man-made barriers external to the dwelling, including but not limited to trees, hills, and adjacent structures. The effective annual solar access shall be 70 percent or greater of the output of an unshaded PV array on an annual basis.”

However, if you file for exemption because your roof is too small or shaded, your regularity agency may explore alternative options for making solar viable on your lot.

How Many Solar Panels Do I Need For an ADU?
The number of solar panels required for newly constructed ADUs under California’s Title 24 depends on the size, location, and projected electrical usage of the ADU. According to the 2022 Building Energy Efficiency Standards, the formula for determining the minimum solar capacity for dwelling spaces is as follows:

kW (PV)required = (CFA x A)/1000 + (NDwell x B, where:
•kW(PV) = kW(DC) size of the PV system
•CFA = Conditioned floor area
•NDwell = Number of dwelling units
•A = Adjustment factor (from Table 7-1)
•B = Dwelling adjustment factor (from Table 7-1)

How Much Does it Cost to Install Solar Panels on an ADU?
The cost of installing solar panels on an ADU varies based on the size and location of the project. But at an average cost of 8 cents per kWh, going solar through solar.com is much cheaper than paying for grid electricity in California.

Average cost (October 2022 prices per Bureau of Labor Statistics):
Los Angeles 25.7 cents per kWh
San Diego 40.9 cents per kWh
San Francisco 30.7 cents per kWh

For Further Reading:
• California Department of Housing and Community Development (HCD) 2020 ADU handbook, stating the solar requirements for ADUs, is at: https://santacruzarchitect.wordpress.com/wp-content/uploads/2023/01/67aee-adutahandbookfinal.pdf