Garage conversion vs. detached ADU: what Title 24 sees differently.
Both need a CF1R. What differs is how each one gets classified — and that classification is what decides whether solar is on the table.
New construction vs. addition is the whole distinction
Both a garage conversion and a new detached ADU need a Title 24 report — that part doesn’t change. What differs is the classification underneath: a newly built detached ADU is a newly constructed building, while a garage conversion is an addition — the Energy Code treats space that becomes newly conditioned as added conditioned floor area, not as an alteration of what was already there. That one distinction is what drives most of the practical differences.
Solar is the biggest one. New construction generally carries the solar PV mandate (see does my ADU need solar for the exceptions). A garage conversion, classified by the Energy Code as an addition rather than a newly constructed building, is generally exempt from that PV requirement — the existing roof and structure aren’t being newly built, they’re being repurposed. Starting in 2027, a single-family lot can carry two detached ADUs, and each one is its own new building with its own solar answer.
Envelope and HVAC requirements apply to both, just measured differently. A detached ADU’s whole envelope is new, so the whole thing gets modeled against current standards. A garage conversion’s existing walls, roof, and slab are evaluated under the addition rules (Section 150.2(a)) — newly conditioned walls generally have to be insulated to the mandatory minimums, but it isn’t a blank-slate model. Either way, if the project also involves an HVAC change-out or new ductwork, that gets modeled specifically.
Neither path is inherently cheaper or slower on my flat rate card — both are priced the same way under 3,000 square feet. The difference shows up in what the model has to account for, not in what you pay.
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.
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.
Garage conversion & ADU classification 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.
Is a garage conversion faster to get through Title 24 than a new ADU?
Does an attached ADU (not detached, not a garage conversion) follow the same rules as a garage conversion?
Not sure which one your project is?
Send the plans either way — the classification, the solar answer, and the report all come back together.