T24Studio
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ADU · California Title 24

Does my ADU need solar?

Generally, yes for a new detached ADU — and an existing system on the main house usually doesn’t cover it. Here’s the actual rule and where the exceptions are.

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The short answer

A new detached ADU generally needs its own PV system

A newly constructed, detached ADU is generally treated as new construction under Title 24 — and new residential construction generally requires a newly installed solar PV system sized for that unit. An existing PV array on the main house doesn’t automatically satisfy the ADU’s requirement on its own — new modules can sometimes be added to an existing array, but they have to be sized and permitted specifically for the ADU, not just left as-is.

There are exceptions that come up often enough to be worth knowing before you assume the worst case:

  • No PV required if the calculated minimum system size works out to under 1.8 kWdc — common on a small ADU footprint.
  • No PV required if the available Solar Access Roof Area is under 80 contiguous square feet — heavy shading or a small/complex roof can trigger this.
  • JADUs and interior or attached ADUs are generally treated as alterations rather than new construction, so they’re generally not subject to the new-construction PV mandate at all.
  • A garage conversion to ADU is generally treated as an alteration too — generally exempt from the same-mandate for the same reason.

“Generally” is doing real work in those sentences — solar sizing depends on the specific project, roof, and how the local building department interprets the exceptions. Send the plans and the model will tell you exactly where your project lands, with the assumption stated plainly, not buried.

Rates

Prices

Flat fees, in writing before I start. No hourly, no bid package, no change-order games — the number on the quote is the number on the invoice.

New client offer

Your first report with me

$150$9924–48 hours

One per client, homes under 3,000 square feet. Full energy model, CF1R and CHEERS registration. It’s a test run — send one job and see how it goes.

Every model after the first

$150Per model

The standard rate once you’re a client — the second building, ADU plus main house, the next project that walks in. Back in 3 business days.

Over 3,000 square feet

QUOTED

Quoted from the plans before any work starts, same day.

24×36 plan-sheet set

$20

Your CF1R laid out full size, matched to your drawing set. Comes back as a PDF you drop straight in.

Revisions

FREEFirst two

Two revisions included, plus questions any time. Past two I quote first, before I touch it.

Commercial / tenant improvement

QUOTEDSame day

Send the plans and you’ll have a flat quote back the same day. No deposit, no minimum.

Process

How it works

  1. 01

    Send the plans

    A PDF of the architecturals and the project address. If something’s missing I ask once, in one email — not five.

    Mechanical and plumbing don’t have to be picked yet. If the plans don’t call out the HVAC or the water heater, I model what I’d normally specify for that job and tell you exactly what I assumed. Change any of it and I’ll rerun — that’s not a revision.

  2. 02

    I build the model

    If the design does not comply as drawn, I tell you what the model needs to pass and the least disruptive way I can find to get there — your call what goes on the drawings.

  3. 03

    You get it back ready to sign

    CF1R registered with CHEERS, you named as the responsible designer. 3 business days — 24–48 hours on your first one. Pay on delivery: Zelle, Venmo or Cash App.

Disclosure

One honest note

I’m not a licensed engineer or architect, and I don’t stamp drawings. On the CF1R I’m the documentation author — you stay the responsible designer. Nothing about your role on the job changes.

That’s on purpose. I’m not after your scope or your clients. I do one piece of the permit set — the piece that usually holds it up — and I do it fast.

Questions

ADU solar questions

If yours isn’t here, see the full FAQ or call and ask.

Does my ADU or addition actually need one?

Almost certainly. New conditioned floor area — ADUs, JADUs, garage conversions, additions — triggers Title 24. So do alterations that touch the envelope, the ductwork, or the HVAC equipment, including a straight change-out. A remodel that only moves non-structural interior partitions usually doesn’t.

Send it either way. If it doesn’t need a report I’ll say so and there’s no charge for the look.

Does a garage conversion ADU need solar?
Generally no — a garage conversion is generally treated as an alteration rather than new construction, which generally exempts it from the new-construction solar mandate that applies to a newly built detached ADU. See garage conversion vs. detached ADU for the fuller comparison.
Does a JADU need solar?
Generally no. A JADU is generally treated as an alteration to the existing structure rather than new construction, which generally puts it outside the new-construction PV mandate that applies to detached ADUs.
Can I just add panels to my house's existing solar array instead of a separate ADU system?
Sometimes, but not automatically. An existing PV system on the main house doesn't by itself satisfy a new detached ADU's separate requirement — any added capacity has to be sized and permitted specifically for the ADU. Whether that's the right approach for your project depends on the array and the ADU's own energy budget — the model settles it.

Find out where your ADU lands.

Send the plans and the CF1R comes back with the solar requirement (or exemption) stated plainly, not buried in an appendix.

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