“Do I have to add solar?”
And the honest answer is: Most of the time, yes — but not always in the way you think.
Solar requirements in California can feel confusing because they depend on how your ADU is built, whether it’s new construction vs. a conversion, and what the local building department requires based on the latest California Energy Code.
In this guide, we’ll break it down clearly so you know what to expect before your project starts.
California’s solar rules come from the state’s energy standards (Title 24), which are designed to:
In simple terms: if you build new living space, California wants it to produce some of its own energy.
Not every ADU requires solar, but most detached new builds do.
Here’s the easiest breakdown:
Yes — solar is typically required.
This includes:
Not always.
Many conversions do not trigger the same solar requirement because you’re converting existing conditioned space rather than building brand-new square footage.
However, this can vary depending on:
Usually no.
JADUs are typically interior conversions, so they usually do not require solar.
Good news: you might not need to add a full new system.
If your home already has solar, the city may allow:
It depends on:
This is where it gets tricky — because it’s not one-size-fits-all.
Your required solar size depends on:
The final solar requirement is calculated through Title 24 energy modeling, and the solar sizing typically happens during plan preparation.
This is actually common — especially with:
If your roof doesn’t work, there may be alternatives such as:
This is another question we get constantly.
In most cases:
No — battery storage is not required.
But some homeowners choose to add a battery for:
Battery storage can also be helpful when the ADU will be used as a rental, since it can reduce peak-time energy costs.
If you’re considering a prefab or modular unit, solar still usually applies if the unit is considered new construction.
That said, prefab solar requirements depend on:
This is why it’s important to work with a builder who understands both:
Solar is an added line item, but it’s also one of the most predictable costs in an ADU project compared to:
Many homeowners are surprised to learn that solar can often be sized efficiently for an ADU — especially when paired with energy-efficient systems.
At ADUs by Avatar, we handle the full process — including:
We make sure the solar portion of your ADU doesn’t become a surprise cost halfway through your build.
If you’re planning a new ADU build in Southern California, solar is something you should expect from day one.
The key is making sure your project is designed correctly so solar:
And most importantly — so it doesn’t slow down your permit timeline.