Your garage already has walls, a roof, and a slab. Turning it into a legal home is mostly about what those parts were never built to do — keep water out from below, carry a dwelling’s loads, hold heat in, and let someone sleep there safely.
A garage conversion is California’s most-used ADU for a reason: the structure is standing, state law gives conversions a protected approval pathway, and the cost is the lowest of any ADU type. But “the structure is standing” is where the easy part ends. A garage was built to shelter cars, not people — its slab, walls, wiring, and ceiling were all allowed to meet a lower standard than a dwelling’s. This guide walks through every layer a conversion has to upgrade, in the order a builder actually checks them, with the state rule or building-code section behind each one. For the project overview, pricing, and timeline, start with our Garage Conversion ADUs hub; this page is the deep dive underneath it.
Watch: Turn Your Garage Into an ADU
The Legal Shortcut: Government Code Section 66323
Most garage conversions in California are approved under Government Code section 66323, subdivision (a)(1) — the conversion category the Department of Housing and Community Development (HCD) calls a “66323 Unit.” HCD’s ADU Handbook (March 2026 edition) summarizes what that pathway guarantees:
- One conversion ADU per lot within the converted space of an existing (or proposed) single-family home or an accessory structure on the lot — a detached garage is the classic case, and HCD confirms sheds and other existing detached accessory structures convert under the same state law (sections 66314(d)(3) and 66323(a)(1), (a)(4)).
- Up to 150 square feet of expansion is allowed — but only to accommodate ingress and egress, such as an entry or a stair. It is not 150 extra square feet of living space.
- No new setbacks. The unit must have exterior access and setbacks sufficient for fire and safety, but it is not subject to the four-foot side and rear setback that applies to new construction — it already sits where it sits, in the same location and to the same dimensions as the existing structure.
- Local design standards do not apply. Objective standards in a local ADU ordinance on height, lot coverage, landscape, design, development, and architecture do not apply to conversions. The one dimensional limit that does apply is built in: a conversion’s height is limited to the dimension of the original structure.
- Building standards fully apply. The exemption is from local zoning standards, not from safety. A conversion must meet all applicable building, health and safety, and fire standards for a dwelling — which is what the rest of this guide is about.
What to verify: that your project is framed as a section 66323(a)(1) conversion on the permit application — existing structure, same footprint, expansion (if any) only for entry. The pitfall: designing a “conversion” that quietly moves walls, raises the roof, or expands the footprint for living space. Past a point, plan check treats it as new construction, and the setbacks, size, and design standards you were exempt from come back.
Can a carport be converted into an ADU?
Yes, with a caveat about what a carport is. State law treats carports alongside garages in its conversion and parking rules — the replacement-parking protection in section 66314(d)(11) expressly names a garage, carport, or covered parking structure converted to an ADU. But a carport is a roof on posts: it has no walls, no slab built for a dwelling, and often no foundation at all. Converting one means building the walls, and frequently the floor and foundation work, that a garage already has — so a carport conversion usually prices and permits somewhere between a garage conversion and new construction, even though it uses the same legal pathway. The pitfall: budgeting a carport like a garage. Get the slab and foundation checked before you rely on the garage-conversion price range.
Can a shed, barn, or other accessory building be converted?
Yes — HCD states it directly: the conversion of detached garages, sheds, and other existing detached accessory structures into ADUs is permitted by state ADU law. The same two-part test applies: the zoning pathway is protected, and the building still has to be brought up to dwelling standards. Small or lightly built structures (a garden shed on skids, a barn with dirt floors) often need so much structural, slab, and utility work that new construction is the honest comparison — which is why the evaluation in the next sections matters more for accessory buildings than for any other conversion type.
Start at the Bottom: Slab Condition, Elevation, and Foundation
Is my garage slab good enough to live on?
The slab is the first thing to check and the hardest thing to change later. A conversion evaluation looks for cracking that shows movement (wide, offset, or heaving cracks, not hairline shrinkage cracks), settling or sloping toward a corner, spalling and deterioration, and evidence the slab is thin or unreinforced at the edges where new wall loads and a raised floor may bear. Many older garage slabs were poured with no reinforcement and no footing at all — fine for a car, not automatically fine for a dwelling. What to verify: slab condition in person, with exploratory cuts or an engineer’s review where cracking or age raises questions. The pitfall: finishing a floor over a slab that is still moving. Cosmetic fixes telegraph through new flooring within a season, and the repair after move-in costs multiples of the repair before framing.
Slab elevation: the step, the slope, and the water line
Garage slabs are usually poured lower than the house floor and sloped toward the overhead door so water runs out. Both facts shape a conversion. The finished floor of the ADU is typically raised above the slab — for moisture protection, insulation, and plumbing runs — which changes the step at every entry and eats into ceiling height (see below). The slab’s slope has to be leveled or built out in the floor system, and the entry has to be detailed so driveway runoff cannot run under the new wall where the door used to be. On lots in a mapped flood hazard area, the finished-floor elevation can be a permit condition, not a preference — check the parcel’s flood status before the floor height is set. The pitfall: picking a finished-floor height off the existing slab alone, then discovering the entry, the ceiling height, or the flood requirement needed two more inches you no longer have.
Does a garage have a foundation that can carry a home?
Some do, some don’t, and you cannot tell from the driveway. Detached garages range from a proper perimeter footing to a slab thickened only at the edge to, on older properties, walls bearing almost directly on a thin slab. The conversion’s structural engineer confirms what is actually there — sometimes with a small excavation at the wall line — and designs what is missing: new footing segments under load points, doweling into the existing slab, or underpinning where walls will carry a second-story or a reframed roof. An attached garage shares the house’s foundation system more often, but the wall between house and garage gets its own checks (see fire separation below). What to verify: foundation adequacy in the structural scope of the plan set, not as a verbal assurance. The pitfall: assuming “it has stood for 40 years” answers the question. It has stood for 40 years as a garage, under garage loads, with no one sleeping in it.
Moisture: The Problem You Cannot See From Inside
Where does moisture get into a converted garage?
Three ways. From below, by capillary action and vapor drive through a slab that was almost certainly poured without the vapor retarder a new dwelling slab gets. From the sides, where the bottom of the wall sits at or below driveway and soil grade, so rain and irrigation water wick into the framing. And from above, through a roof and flashing that were maintained to a garage standard. The symptoms in finished conversions are consistent: musty odor, flooring that cups or lifts, mold at the base of walls, and paint that peels at floor level. What to verify: how the design handles all three paths — a slab moisture strategy, a raised and flashed wall base, and roof/flashing repairs in scope. The pitfall: treating moisture as a flooring problem. By the time the floor shows it, the source has been wetting the wall bottoms for months.
What is a capillary break, and why does a garage need one added?
A capillary break is a non-porous layer that stops water moving upward through concrete and masonry by wicking. New dwelling slabs get one by code: CRC section R506.2.3 requires a vapor retarder at least 10 mils thick under a slab-on-grade, with joints lapped at least 6 inches — and garages were expressly excepted from that requirement while they were garages, which is why an existing garage slab almost certainly has none. A conversion therefore retrofits the function instead of the layer: typically a surface-applied moisture-mitigation coating or membrane system on the slab before flooring, a capillary break under new sill plates and at the raised floor, and flooring selected and warranted for the slab’s measured moisture level. What to verify: that the plan set and the flooring specification name a slab-moisture system, and that moisture testing happens before the floor goes down. The pitfall: laying luxury vinyl or wood directly on a bare garage slab because it “looked dry.” Concrete that looks dry in August can still pass enough vapor to fail an adhesive floor in its first wet winter.
Framing the New Room: Door Infill, Ceiling Height, and the Roof
What happens to the garage door opening?
The wide opening is the conversion’s biggest framing job and its weakest structural link until it is done. The usual approach keeps the existing header where it is sound and builds a framed, insulated, sheathed wall inside the opening — often with a window or the unit’s entry door in it, which is one place the 150-square-foot ingress/egress expansion and a new entry stoop can come in. The structural questions are shear and load: the old opening was a deliberate hole in the wall’s bracing, and the infill wall has to restore the wall line’s resistance to lateral loads, tie into the slab, and be flashed so the old driveway apron sheds water away from it. What to verify: the infill detail in the structural plans, including how the new wall anchors and how the threshold is waterproofed. The pitfall: a cosmetic infill — studs and siding with no shear value and a flat threshold. It looks finished, leaks at the first driven rain, and fails the framing inspection it should have been designed for.
How much ceiling height does a garage conversion need?
The California Residential Code sets the floor: habitable rooms and hallways need a ceiling height of not less than 7 feet, and bathrooms, toilet rooms, and laundry rooms not less than 6 feet 8 inches (CRC section R305.1). Garages fight this number from both directions — the slab is low and often sloped, the finished floor has to rise above it for moisture and plumbing, and the existing ceiling or roof framing was never checked against a 7-foot finished room. Measure the worst point, not the best: the height that matters is from the finished floor to the finished ceiling at the low end of the old slab slope, after floor build-up and any dropped soffits for ducts. Sloped-ceiling rules allow part of a room below 7 feet, but at least half the required floor area must reach the full height. The pitfall: approving a plan drawn off the garage’s open, unfinished dimensions. Insulation, drywall, floor build-up, and a level floor over a sloped slab can quietly take three to five inches that a tight garage does not have to spare.
Can the existing roof framing stay?
Often, yes — but it has to be verified, not assumed. Garage roofs were framed for roofing and storage loads, with trusses or rafters that may be undersized, widely spaced, or cut and altered over the years for pull-down stairs and storage platforms. A dwelling ceiling adds insulation, drywall, and sometimes a second story or a storage attic above, and the conversion’s engineer checks the existing members against current loads and either clears them, reinforces them (sistering, added bearing), or designs replacements. This is also where a raised or vaulted ceiling is won or lost: removing a flat garage ceiling to vault into the roof changes the structure, not just the look. What to verify: roof framing in the structural scope, with any attic storage or future second-story ambitions stated before the engineer runs the numbers. The pitfall: discovering undersized rafters at framing inspection, when the fix is no longer a line on a plan.
Insulation and the Energy Code
Do garage walls have to be insulated to dwelling standards?
Yes. A garage’s walls are typically a single stud depth with no insulation, no air sealing, and siding or stucco straight over framing. As a dwelling, the walls, ceiling/roof, and floor become the unit’s thermal envelope and must be insulated and air-sealed to the California Energy Code (Title 24, Part 6) requirements the plan set’s energy documentation demonstrates — the same compliance paperwork every ADU files, prepared for this unit’s actual assemblies. The California Energy Commission’s ADU guidance classifies a conversion of an existing unconditioned space — a garage, attached or detached — as an addition under the Energy Code, complying under section 150.2(a), not as a newly constructed building. In practice that means cavity insulation in the stud walls (and sometimes added depth or continuous insulation where the existing studs are shallow), a fully insulated ceiling or roof deck, and detailing at the slab edge and the door-infill wall, which are the two places conversions most often leak heat. Two addition-specific rules from the CEC’s ADU FAQs are worth knowing at design time: existing 2×6 walls on a conversion can comply prescriptively with R-21 cavity insulation, with no continuous insulation required on those walls (section 150.2(a)1Ai); and the prescriptive Quality Insulation Installation requirement does not apply to ADU additions of 700 square feet or less (section 150.2(a)1Bv) — a category most garage conversions fall inside. One energy consequence saves conversions real money: the solar photovoltaic system the Energy Code requires for a newly constructed detached ADU (section 150.1(c)14) is a new-construction requirement, and the CEC states the point outright for attached ADUs — no PV required, because they are additions. A garage conversion’s energy budget goes to its envelope, systems, and lighting instead. What to verify: the energy features are in the plans and the budget before framing — insulation is a named line in a proper conversion bid, not an assumption. The pitfall: the “insulate it later” conversion. A converted garage without a real envelope is the unit tenants describe as freezing in winter and an oven in summer, and opening finished walls to fix it costs what the whole insulation package would have, several times over.
Wiring and Plumbing a Space That Was Never a Dwelling
Can a garage’s electrical wiring serve an ADU?
Almost never as-is. A garage typically has one general circuit, a door-opener outlet, and lighting — a dwelling needs dedicated kitchen and bathroom circuits, laundry and appliance circuits, heating and cooling loads, and the full set of safety protections current code requires in living space, all of it usually fed from a new subpanel or an upgraded service. The panel-capacity question belongs to the whole property, not just the garage: the conversion is the right moment for a proper load calculation on the main service, because an ADU added to an already-loaded panel is one of the most common mid-project surprises in ADU work generally. What to verify: a load calculation and a panel plan in the electrical scope, before the bid is signed. The pitfall: a conversion bid that says “electrical included” with no panel work anywhere in it — the upgrade then arrives as a change order at rough-in, when there is no leverage left.
How close does the plumbing have to be?
Plumbing is where garage location makes or breaks a conversion budget. Water supply is usually the easy half — lines can be extended from the house or run in the new floor. Drainage is the governing half: the new bathroom and kitchen drains must reach the building sewer with continuous fall, and a garage at the far end of the lot, or sitting low relative to the sewer connection, can mean a long trench across the yard, a deeper connection, or in the worst geometry, a sewage ejector. One state rule helps conversions specifically: an ADU created from existing space under section 66323(a)(1) cannot be required to install a new or separate utility connection unless it is built at the same time as a new single-family home (sections 66311.5(d), (e)) — the conversion connects through the existing services. What to verify: the sewer connection point and its depth, ideally with a camera inspection of the existing lateral before design — an old clay or cast-iron lateral that is already failing is far cheaper to replace while the yard is open for the conversion trench. The pitfall: designing the bathroom at the far end of the garage from the sewer, then paying for every extra foot of trench, depth, and restoration the layout created.
Where do the bathroom and kitchen fit?
Inside a two-car footprint — usually around 400 square feet — layout is a zero-sum puzzle, and the wet rooms drive it. The efficient pattern clusters the bathroom and kitchen on one shared “wet wall” as close to the sewer route as the plan allows, keeps the bathroom’s required clearances honest (fixtures cannot be squeezed below code minimums just because the footprint is tight), and puts the bedroom where the egress window and the quiet side of the lot are. Stacking the kitchen over the bathroom’s plumbing wall, or back-to-back across it, shortens both drain and vent runs. What to verify: the layout against the sewer direction and the window wall, not just against the furniture you want to fit. The pitfall: falling in love with a floor plan that puts the bathroom in the one corner the drains cannot reach without a pump — see our ADU floor plans for layouts that work inside a two-car footprint.
Kitchen and bathroom venting
A dwelling’s wet and cooking spaces must exhaust moist, contaminated air directly outdoors — a garage’s passive vents do not count. For bathrooms, the California Residential Code requires either a window of at least 3 square feet (half openable) or mechanical exhaust — 50 cubic feet per minute intermittent or 20 cfm continuous, ducted directly outside — and bathrooms with a tub or shower must have mechanical humidity-control ventilation regardless of windows (CRC sections R303.3, R303.3.1). Kitchens need a range hood or other local exhaust ducted to the outdoors, sized under the California Mechanical Code and the Energy Code’s kitchen-exhaust rules (Title 24, Part 6, section 160.2) — a recirculating hood alone does not satisfy a new ADU kitchen’s requirements where the code calls for ducted exhaust. The pitfall: venting into the attic or the old garage roof cavity. It passes a glance, fails inspection, and pumps a shower’s worth of moisture into the roof framing every day.
Windows: Egress, Daylight, and Ventilation
Every sleeping room needs an escape window
This is the code rule that most changes a garage’s walls. Under CRC section R310, every sleeping room (and basement and habitable attic) needs at least one operable emergency escape and rescue opening, sized so a person can climb out and a firefighter can climb in: a net clear opening of at least 5.7 square feet (5.0 square feet for a grade-floor opening), at least 24 inches high and 20 inches wide in net clear dimensions, with the bottom of the opening no more than 44 inches above the floor (CRC sections R310.2.1–R310.2.3). Most garage walls have no window anywhere near that size — small, high garage windows fail on both size and sill height — so a conversion normally cuts at least one new, properly sized opening in the bedroom wall, with the header, flashing, and (near a property line) fire-separation questions that come with it. One conversion-specific relief exists: where a change of occupancy triggers the egress requirement, CRC section R310.7.1 allows certain existing operable windows to comply at a smaller size — 4 square feet net clear, 22 inches high, 20 inches wide — but whether it applies to your garage is your building department’s call, so verify it at plan check rather than designing around it. The pitfall: counting an existing garage window as the bedroom’s egress on a plan. It is the single most common reason a conversion plan comes back with corrections.
Daylight and fresh air
Habitable rooms also need glazing of at least 8 percent of the room’s floor area, and openable area of at least 4 percent for natural ventilation, unless the design uses the code’s mechanical-ventilation alternatives (CRC section R303.1). A windowless or small-window garage starts far below both numbers, which is why conversions typically add windows beyond the one egress opening — and why the window plan belongs in the first design pass, balanced against privacy from the main house and the fire-separation limits on openings in walls close to a property line. What to verify: the light and ventilation math room by room on the plans. The pitfall: a legal-but-dark unit. Meeting egress alone leaves a room that technically sleeps one and feels like a closet; the daylight numbers exist precisely to prevent that outcome.
Fire Separation When the Garage Is Attached
Two different fire questions get confused in attached conversions, and they have different answers. The first is sprinklers: a conversion cannot be made to add fire sprinklers the primary residence is not already required to have, and building the ADU cannot trigger a sprinkler requirement for the main house (sections 66314(d)(12), 66323(d)) — our fire sprinkler guide covers that rule in full. The second is separation. Where part of a garage remains a garage next to new living space — the classic case is converting one bay of a multi-bay or attached garage — the wall and ceiling between the remaining garage and the dwelling must meet the dwelling-garage separation in CRC sections R302.5 and R302.6: at least ½-inch gypsum board on the garage side of the wall, ⅝-inch Type X gypsum where habitable rooms sit above the garage, no opening from the garage directly into a sleeping room, and any door between garage and home a solid or 20-minute-rated, self-closing and self-latching door. Where the entire garage becomes the ADU, the wall it shares with the main house stops being a garage wall and is treated as a dwelling separation in the plan set — your plan checker confirms the assembly, but it is designed and inspected either way, never just left as the old garage drywall. The pitfall: assuming “no sprinklers required” means “no fire work required.” Separation, alarms, and egress are separate requirements, and conversions are held to all of them.
The Driveway After the Garage Is Gone
Converting the garage does not convert the driveway — and state law is specific about the parking. A city cannot require the off-street parking spaces lost in a garage, carport, or covered-parking conversion to be replaced (section 66314(d)(11)), and an ADU created within an existing accessory structure is itself exempt from ADU parking standards (section 66322(a)(3)). What physically happens to the driveway is a design decision with practical consequences: it usually stays as the ADU’s entry walk and access path (and often as the household’s remaining parking, in front of what is now a front wall), its drainage pattern has to be kept away from the new infill wall, and on many lots it becomes the construction access route — which is why its condition and width get noted at evaluation. What to verify: where the ADU’s entry path, trash bins, and mail access actually go once the driveway’s destination changes, and whether your street’s on-street parking rules work for your household’s cars. The pitfall: discovering after the conversion that the household’s real parking plan was the garage all along. The law says the city cannot make you replace the spaces; it does not park your cars.
The Paper Trail: Existing Permits and Unpermitted Work
Does it matter whether my garage itself was permitted?
Yes — it decides how much archaeology your project starts with. A garage built with the house and finaled on the original permit is a clean starting point. A garage that was added, expanded, or partially converted over the years without permits carries that history into your application: the conversion permit is the moment the whole structure has to be shown as a legal dwelling, and work that was never inspected — a bonus room over the garage, a bathroom roughed in “for later,” a water heater and panel added informally — has to be documented, brought to current standards where the code requires it, or removed. A permit-history search at your city or county, plus whatever the seller disclosures and assessor records show, is part of a proper evaluation. What to verify: the garage’s permit record before design, and whether anything attached to it (additions, mezzanines, plumbing) appears on any permit at all. The pitfall: a conversion bid priced on a permitted garage that turns out to be an unpermitted one. The design and correction scope is different work.
What if the garage was already converted without a permit?
Then the project is a legalization, and California law gives it a real pathway. For an unpermitted ADU built before January 1, 2020, a city generally cannot deny the legalization permit just because the unit violates building standards, state ADU law, or the local ADU ordinance — denial requires a finding that correction is needed to protect the health and safety of the public or the occupants, or that the building is substandard under Health and Safety Code section 17920.3 (section 66311.7). Before applying, a homeowner may also obtain a confidential third-party code inspection from a licensed contractor to learn the unit’s condition and likely correction scope without starting the official clock. Health and safety corrections are still real work — egress, alarms, sanitation, and structural safety are exactly the items a legalization has to prove — and the CEC adds one more: unpermitted work permitted now must meet the applicable current Energy Code requirements, with the building department deciding whether the unit complies as a newly constructed building or as an addition. So a lived-in unpermitted conversion should be budgeted as a conversion plus a correction allowance, not as paperwork alone. Our ADU FAQs cover the related legalization questions, including the related rules for unpermitted units built on or after January 1, 2020. The pitfall: assuming an unpermitted conversion is “grandfathered” when you sell or refinance. Lenders, appraisers, and insurers treat it as what it is — unpermitted space — until the legalization permit finals.
Conversion vs. New Construction: The Honest Comparison
On headline price, a conversion wins every time — and the reasons are structural. You are not buying a foundation, four walls, and a roof; you already own them. Using the same price ranges as our ADU cost guide:
| Path | Typical total range | What the range assumes |
|---|---|---|
| Garage conversion | $100,000–$200,000 | Existing slab, walls, and roof are sound enough to keep; the budget goes to moisture protection, infill framing, insulation, full plumbing/electrical, and finishes. |
| Attached ADU (new construction) | $180,000–$300,000 | New addition sharing one wall with the house — new foundation, framing, and roof, but shared systems and a shorter utility run. |
| Detached ADU (new construction) | $250,000–$450,000 | A standalone backyard home: full foundation-to-roof build plus trenching and utility runs across the yard. |
Where the comparison narrows: a conversion whose slab needs major repair, whose foundation needs underpinning, or whose roof framing needs replacement is quietly buying back the items that made it cheap, and its true cost walks toward the attached range. Where it widens: conversions carry no replacement-parking cost, usually permit and build fastest of the three paths, and keep the yard intact. What to verify: the comparison on your garage’s actual condition report, not on the category averages. The pitfall: choosing the conversion on the $100,000 end of the range before anyone has looked at the slab, the footing, or the roof — the three inspections that decide which end of the range is real.
How a Conversion Is Built: The Sequence
Conversions feel fast because the shell exists, but the work inside it follows the same disciplined order as any dwelling build. Skipping ahead in this sequence is how moisture systems get buried and inspections get failed:
- Evaluation and permit history — structure, slab, sewer, panel, and the garage’s own permit record, before design money is spent.
- Design, engineering, and energy documentation — layout around the wet wall and egress wall, structural design for the infill and any foundation work, Title 24 paperwork.
- Permits — ministerial review under the section 66323 conversion pathway; the plan set has to prove dwelling standards, which is where complete first submittals pay for themselves.
- Strip-out and slab work — demolition of garage interiors, slab repairs or cutting for plumbing, moisture-mitigation system, foundation work where designed.
- Framing — door-opening infill, interior walls, window and door openings including the egress window, roof framing repairs or reinforcement.
- Rough trades — plumbing, electrical, and mechanical run and inspected before anything is covered.
- Insulation and drywall — the thermal envelope goes in only after rough inspections pass.
- Finishes and fixtures — flooring rated for the slab’s moisture system, cabinets, fixtures, and appliances.
- Final inspection and sign-off — the unit becomes legal living space; keep the finaled permit and plans with your property records.
Our ADU timeline guide puts realistic durations on each phase; the conversion advantage shows up mostly in steps 4 and 5, where a new build is still pouring and framing its shell.
Before You Sign: A Garage Conversion Checklist
- Confirm the project is framed as a section 66323(a)(1) conversion — existing structure, same footprint, any expansion only for ingress/egress.
- Get the slab checked (condition, elevation, moisture) and the foundation verified in the structural scope — in writing, not verbally.
- Confirm the finished ceiling height at the worst point clears 7 feet after the floor is raised and leveled.
- Place the bedroom where a code-sized egress window can actually go, and run the 8 percent daylight / 4 percent ventilation math room by room.
- Camera the sewer lateral and confirm the connection depth before the bathroom location is fixed.
- Get a load calculation for the main panel; make sure panel work is a named line in the bid if it is needed.
- Pull the garage’s permit history; price unpermitted elements as their own scope.
- Decide the driveway’s new job — entry path, remaining parking, bin and mail access — before the infill wall is designed.
We check the slab, structure, ceiling height, sewer, and panel on your property — and tell you straight which end of the conversion range you are really on.
Call 888-627-1131 Get a Free ConsultationSources (verified October 2026): California Department of Housing and Community Development, Accessory Dwelling Unit Handbook, March 2026 edition — 66323 Units, ADU Conversions, Parking, Fire Sprinkler, and Unpermitted Units sections; Government Code Sections 66311.5, 66311.7, 66314, 66322, 66323; California Residential Code Sections R302.5, R302.6, R303.1, R303.3, R305.1, R310, R506.2.3; California Energy Code (Title 24, Part 6) Sections 150.2(a), 150.1(c)14, 160.2, and the California Energy Commission’s 2025 Energy Code ADU FAQs (conversions of unconditioned space are additions; solar PV is a newly-constructed-detached-ADU requirement). This page is part of the California Accessory Dwelling Unit Handbook on this site (Garage Conversions, Questions 701–750, plus carport and accessory-building conversions from Types of ADUs). Related: Garage Conversion ADUs · ADU Cost Guide · ADU FAQs
