California applies a common set of ADU and JADU standards to every city in the state. Answer six questions and see how your parcel measures up on size, setback, height and whether a JADU can be added alongside. What comes back is a screening, not an approval.
Nothing here is a quote, a bid, an engineering determination or a boundary determination. We are a drafting and design firm: we coordinate with a licensed structural engineer and a Licensed Land Surveyor when your project needs one, rather than performing or stamping that work ourselves.
It helps to picture California's ADU statute as a floor rather than a ceiling. A city generally may not refuse an ADU of 800 square feet at 16 feet tall with 4-foot side and rear setbacks, no matter how the local ordinance reads. That protection is the reason parcels that look hopeless on an assessor map still work out. Coverage caps, floor area ratios, minimum lot sizes and open-space standards generally cannot be stacked up to push an ADU under that floor.
Move above the floor and the familiar framework takes over. Detached units are commonly allowed up to 1,200 square feet. Attached units are generally held to half the floor area of the main house, still with the 800 square foot protection underneath. JADUs stop at 500 square feet, sit inside the existing or proposed walls of a single-family dwelling, connect to the main house internally, include an efficiency kitchen, and carry an owner-occupancy condition on one of the two units. Because an attached garage is inside those walls, it can become a JADU. A detached garage is not, so converting one is simply a regular ADU. Conversion projects are sized by the footprint already standing, and trading a garage for an ADU does not oblige you to rebuild the parking space you lost.
Everything wrapped around that box stays local: how deep the front yard runs, whether design and materials get reviewed at all, how far past the state floor you may build upward, which trees are protected, how wide the driveway and the fire lane have to be, the way the site grades and sheds water, what the sewer lateral can carry, and what the impact fees add up to. Drop the same parcel in Sunnyvale and then in Los Gatos and the buildable answer can shift for reasons that have nothing to do with ADU law. That is precisely why the jurisdiction, not this page, has the last word.
Once the size question settles, the rest is drafting. Expect floor plans, an elevation of every exterior face, sections cut through the building, a site plan that dimensions the setbacks and the separation from the main house, details covering assemblies and egress, a schedule listing every door and window, power and plumbing layouts, and a registered Title 24 report riding alongside all of it. That package is what our ADU and JADU design service produces, and the Title 24 CF1R energy calculations page explains why an ADU gets modeled differently from an addition.
Foundation design for a detached unit, or a shear wall that disappears when the garage door opening is infilled, calls for structural sheets and calculations. An independently licensed engineer we bring onto the project draws and stamps those. We assemble and reconcile the rest of the set; every engineering judgment, and the stamp itself, belongs to the engineer. No firm can hand you a plan check result in advance, but a complete set whose sheets agree with each other is the most reliable way to keep the correction list short.
On a single-family parcel, state law generally permits the pair. The JADU stops at 500 square feet, has to fall inside the existing or proposed walls of the house, connects internally to the main dwelling, includes an efficiency kitchen, and comes with an owner-occupancy condition on one of the two units. Duplex and multifamily parcels run under a different set of allowances and JADUs are generally off the table there. Your jurisdiction confirms what applies to your address.
It depends on whether the garage is attached. An attached garage sits within the walls of the single-family house, which is the defining JADU condition, so it qualifies. A detached garage does not, and converting one is screened as an ordinary ADU instead. Either way the existing footprint caps the project unless you expand past it, at which point you are building new construction.
Rarely. State law generally stops a local coverage limit, floor area ratio or open space standard from shrinking an ADU below 800 square feet at 16 feet with 4-foot side and rear setbacks. That is exactly why constrained parcels still pencil. It does not suspend fire access, recorded easements or flood requirements, so those remain on the checklist with the city.
Generally not, when the result is an ADU. State law waives replacement parking for that case specifically. Turn the same garage into a bedroom, office or family room instead and the waiver does not follow, so your local zoning may still want the off-street space accounted for somewhere on the lot.
No. All this does is line your answers up against statewide minimums. It has no view of your zoning district, easements, fire access, utilities or protected trees, it is neither a zoning nor a boundary determination, and it cannot commit a city to anything. Verify at the planning counter before you design to any figure on this page.
No. Sunny Drafting & Design handles drafting, design, Title 24 and permit documentation. We deliver the drawings and compliance documents you submit, we bring in an independently licensed engineer when structural design or a stamp is called for, and a Licensed Land Surveyor when a boundary survey is. Your contractor does the building.
Residential or commercial, drafting or Title 24 — send a few details and we'll follow up with next steps and a free quote.
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