All New Single Family Residential constructions and ADUs are mandatorily required to have solar per the 2022 energy code (in fact this was applicable since the 2016 energy code), except for a few exceptions.
Firstly, is your home or ADU a New Construction?
Before we get into the exceptions, let's first make sure your project IS a New construction. If you are doing an “addition” to your home (such as adding a few SF) or an “alteration” to your home (such as window replacements or kitchen remodel, etc), then this is NOT a New construction and hence won’t trigger solar requirements. If you are building something New from the ground up, and there was nothing else that stood there previously or if you completely demolished what stood there previously. Only then the project is to qualify as a New Construction.
The above is all the more important for ADUs. Only new construction ADUs need solar. New Construction ADUs are ones that are detached and built from the ground up. If they are attached they are "additions" or "alterations" and not a "new construction", and hence don't need solar. Similarly, if they are detached but a conversion (such as a garage conversion to ADU or pool house conversion to ADU) or even if they are built attached to an existing garage (such as on top of the garage or share an interior wall), they qualify as "addition" and not "new construction", and hence don't need solar. So essentially for ADUs, new detached constructions that are not conversion (built from the ground up), qualify as a New Construction and hence might need solar.
Calculating Required PV Size per the 2022 Energy Code
The required solar size for Single Family Residence and ADU New Constructions depends on the conditioned floor area and climate zone. And if the required solar size is < 1.8 kW then we can claim an exception and won't require solar.
The required solar size is calculated by Equation 7-1 in the code, which is:
Required PV in kW = (Conditioned Floor Area x A) / 1000 + (Number of Dwelling units x B). Here A and B are adjustment factors mentioned in the table 7- A in the code. Both of them are dependent on the climate zone.
If any doubt which climate zone your project falls under, you can use the below tool from the California Energy commission. It will help you confirm the climate zone per the zip code of the project.
So if we work backwards from 1.8 kW and take the number of dwelling units as 1 (for single family residences and ADUs), we get the approximate conditioned floor area below which we can claim the exception and won’t need solar.
For climate zone as 7 (for San Diego and Oceanside):
1.8 kW = (CFA x 0.572)/1000 + (1 x 1.15)
From the above, we get the CFA = 1136 SF. So as a thumb rule, on most single family residential projects and ADUs in CZ 7, you won't need solar up to ~ 1100 SF.
Similarly, for climate zone as xx (past of Los Angeles)
Similarly, for climate zone as xx (San Francisco)
A few other Exceptions
Besides the above, there are a few other exceptions that can be claimed but those are very site dependent and require additional documentation proving that the site qualifies for them. These include insufficient solar access (such as if there are tall trees around the site that block the sun) or if there is high snow load or if the project is a fire re-build in a declared emergency area etc.
A few Caveats
Please note that all of the above is for projects that fall under the 2022 energy code. For the previous 2019 energy code, the 1.8 kW exception mentioned above is not available.
Also, please note that certain counties have local reach codes that supersede the above exceptions or might require a larger sized PV system. It’s best to address this once we start working on your Title 24 calculations.
Please note that the above is for single family residential projects. For multi-family, high rise or non-residential projects, the PV requirements and exceptions are different.
Please note that there is a difference between solar requirement and solar ready requirement. Solar requirements supersede solar ready requirements.