Most people meet the solar requirement late, from their contractor, as a surprise line on a bid. The number is usually smaller than they expect, and what drives it is rarely the panels.

The questions people actually ask

Does my ADU actually need solar?

It depends how it’s built. A newly constructed ADU is generally treated as a new dwelling unit under Title 24; a garage conversion can land differently. The document that settles it is your CF1R — the Title 24 compliance report your energy consultant or architect produces. It states the required size in kilowatts. If nobody has shown you one, ask before you accept any solar number.

How big does it have to be?

Smaller than people expect. The requirement scales with conditioned floor area, and an ADU is a fraction of a house — so the required system is usually a fraction of a house system. Anyone quoting a whole-house-sized array for an ADU should be able to explain why.

Does it get its own meter, and does that matter?

It matters more than almost anything else on the bid. A separately metered ADU is a separate system: its own array, its own home run, its own interconnection application. Sharing the main house service is a different design and usually cheaper. Your plans and your utility decide which you have — not the solar company.

Can the panels go on the main house instead?

Sometimes, if the ADU is on the same meter and the main roof has the room and the orientation. If it’s separately metered, its production generally has to serve its own meter. Worth asking early — the answer changes where the scaffolding goes.

When in the build does this happen?

Usually as a deferred submittal: the solar plan set is permitted separately from the main permit, by the licensed contractor doing the install. That’s normal. What isn’t normal is finding out the week before you want a certificate of occupancy.

How to tell if you’re being upsold

This is the part nobody writes down, so here it is.

What we do on an ADU

We read the CF1R and the plans, tell you what’s actually required, and size to that unless there’s a reason to go further — which we’ll explain rather than assume. The installation is performed, permitted and warranted by a CSLB-licensed contractor we name before you sign, and your contract is with them.

If you want a second opinion

Send us the CF1R and whatever number you have been quoted. We will tell you what we see, whether or not it turns into anything. If your ADU does not need what you are being sold, that is a short email and it costs you nothing.