Multifamily ADUs in California: Conversions, Detached Units, and the SB 1211 Rules

An apartment property is the largest ADU opportunity in California law — and the most miscounted. Since SB 1211 took effect on January 1, 2025, a lot with an existing multifamily building can add converted units inside the building and detached units outside it, and the two allowances stack. This guide works through the actual formulas in Government Code §66323, what “non-livable space” really covers, what happens to tenants, parking, and common areas, and the questions state law pointedly does not answer — there is no state phasing rule, no state common-area rule, and no state rule that lets an owner displace a tenant’s home to build an ADU.

This page is general information about California law as of November 2026, not legal advice for your property. Local ordinances, rent-stabilization rules, and fire-district standards can add requirements the state rules below do not; confirm your parcel with your city and, for tenant questions, a California landlord-tenant attorney. This page is the Multifamily Properties chapter of our California Accessory Dwelling Unit Handbook. The law itself is summarized on California ADU Laws (the SB 1211 section); the income side is on ADU Rental Income in California.

What Counts as a Multifamily Property?

Start with a surprise: Government Code §66313 — the ADU chapter’s definitions section — never defines “multifamily dwelling.” Its defined terms cover the ADU itself, accessory structures, JADUs, livable space, and living area, but there is no multifamily definition and no statutory unit-count threshold (nothing in the chapter says multifamily means five units, or any other number). The operative language lives in §66323 itself, which speaks of an “existing multifamily dwelling,” its “structures,” and its “units.”

The working definition is the California Department of Housing and Community Development’s (HCD), and we publish it as HCD’s guidance, not as a statute: a structure with two or more attached dwelling units on a single lot is a multifamily dwelling structure; multiple detached single-family houses on the same lot are not (HCD ADU Handbook, Glossary and Multifamily FAQs). Two consequences follow:

• An attached duplex fits the multifamily pathways under HCD’s gloss; two detached houses on one lot do not — that lot uses the single-family pathways instead.
• “Existing” versus “proposed” is load-bearing. Interior conversions exist only in an existing multifamily structure. Detached ADUs reach lots with an existing or proposed multifamily dwelling — at different caps (below). A “proposed dwelling” is one that is itself the subject of a permit application meeting the requirements for permitting (§66313(l)); an intention to build is not a proposed dwelling.
• The zone test: §66323’s ministerial approvals apply to a building-permit application within a residential or mixed-use zone.

Three framing rules apply to every multifamily ADU in this guide. No junior ADUs: JADUs live in single-family zones under §66333, and HCD’s Multifamily FAQ answers “Can JADUs be created in multifamily dwelling structures?” with a flat “No.” No owner-occupancy: a local agency cannot impose an owner-occupancy requirement on these ADUs (HCD’s reading of §66315, reinforced for §66323 units by §66323(b) below). Long-term rentals only: for any unit created under §66323, the agency shall require rentals for terms longer than 30 days (§66323(e)) — that sentence expressly reaches the multifamily conversion and detached units in this guide. And an ADU may be rented separately from the primary residence but may not be sold or conveyed separately from it, except through the local-opt-in separate-conveyance lane of §§66340–66342 (§66314(d)(1)).

Counting the Existing Units: Two Different Bases

Every multifamily number in this guide is a percentage or a cap of a count — and the statute uses two differently worded counts. Do not blend them:

• The conversion base (§66323(a)(3)(B)) is “the existing multifamily dwelling units” — the units in the existing building.
• The detached base (§66323(a)(4)(A)(ii)) is “the number of existing units on the lot” — worded lot-wide.

Both counts are existing units — never a proposed count, never a rent roll that already includes the ADUs you want to add, and never an assessor record that lags the legal unit count. Confirm the legal existing count with the city at intake; it decides everything downstream. Two things the sources do not say, published here as open questions rather than answers: neither §66323 nor the Handbook states a rounding rule for the 25 percent conversion figure (25 percent of six units is 1.5 — fractional cases are a confirm-at-intake item; the only safe statements are “at least one” and “up to 25 percent”), and neither states whether an unpermitted unit counts toward either base (legalization under §66311.7 is a separate lane).

The Detached Allowance — and Why “Eight” Is Not the Ceiling

Section 66323(a)(4) allows detached ADUs on a lot with an existing or proposed multifamily dwelling, detached from that dwelling, with rear and side setbacks of no more than four feet. The caps, read exactly:

• Existing building: “not more than eight detached accessory dwelling units. However, the number … shall not exceed the number of existing units on the lot.” The allowance is the smaller of eight and the existing unit count.
• Proposed building: not more than two detached ADUs.
• Heights come from §66321(b)(4): 16 feet for a detached ADU on a lot with an existing or proposed single-family or multifamily dwelling; 18 feet within a half-mile walking distance of a major transit stop or high-quality transit corridor, plus an additional two feet to accommodate a roof pitch aligned with the primary dwelling’s; and 18 feet on a lot with an existing or proposed multifamily, multistory dwelling.
• No forced fix of the existing building: if the existing multifamily dwelling already sits closer than four feet to a rear or side line, the agency shall not require any modification of it as a condition of approval (§66323(a)(4)(B)).

The most common live defect in city handouts: a cap of two detached ADUs for an existing building. That was the pre-2025 rule. Since SB 1211 took effect on January 1, 2025, two is only the proposed-building number. And the second miscount runs the other way: the eight-unit ceiling caps detached units only. Section 66323(a) authorizes the listed units “or any combination” of them, so conversions inside the building (next section) stack on top of the detached count:

Arithmetic on the verified formulas only; fractional conversion counts are confirm-at-intake (no rounding rule exists). HCD adds that, in addition to the §66323 units, a local agency must allow at least one unit under its §66314 ordinance (Handbook, p. 18) — subject to that ordinance’s objective standards. One size caution: §66323 states no size condition for conversion or multifamily detached units (contrast the 800-square-foot condition written into the single-family detached paragraph, §66323(a)(2)). We do not convert that silence into an “unlimited size” claim — how a city treats the size of these units is a confirm-at-intake item.

Converting Non-Livable Space Inside the Building

The interior pathway is §66323(a)(3). A local agency shall ministerially approve multiple ADUs within the portions of existing multifamily dwelling structures that are not used as livable space — “including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with state building standards for dwellings” (§66323(a)(3)(A)). The count is at least one, and up to 25 percent of the existing multifamily dwelling units (§66323(a)(3)(B)).

“Livable space” is a defined, functional test: “a space in a dwelling intended for human habitation, including living, sleeping, eating, cooking, or sanitation” (§66313(e), added by SB 1211). Space not used for those five purposes is the conversion pool, and the statutory list is expressly non-exhaustive. HCD affirms examples beyond the list: a leasing office inside the building converts under (a)(3) (Handbook Multifamily FAQ), and the Handbook’s combinations table names gyms and enclosed parking within the multifamily structure. Three limits shape every conversion project:

• The building-standards condition is inside the entitlement. A conversion that cannot meet state building standards for dwellings — light and air, egress, sanitation, ceiling height — is outside (a)(3)(A), however clear the zoning entitlement is. The life-safety sections below are where conversion projects are actually won or lost.
• No extra standards. “A local agency shall not impose any objective development or design standard that is not authorized by this section” on a unit that meets §66323’s requirements (§66323(b)). HCD reads that to include parking, lot size, open space, and floor-area-ratio standards. Nor may an agency require correction of a nonconforming zoning condition as a condition of ministerial approval (§66323(c)).
• The occupancy-code sentence applicants miss. ADU construction generally “shall not constitute a Group R occupancy change” unless the building official makes a written finding, on substantial evidence, of a specific adverse impact on public health and safety — but §66314(d)(8) expressly preserves the agency’s power to change the occupancy code of a space that was uninhabitable or permitted only for nonresidential use and is converted to residential use. Publish both halves in your project plan: the conversion of a boiler room or garage level to dwellings is an occupancy change in the building code’s eyes, with the fire and egress work that follows.

Space in a proposed building has no (a)(3) pathway — interior units in a building that does not yet exist are primary units, not ADUs. And space that is in fact livable — a rented room, an occupied manager’s unit, anything used for sleeping, cooking, or sanitation — is outside (a)(3)(A) entirely; the tenant section below explains why that line is also the displacement line.

Storage rooms: expressly in

Storage rooms are the first space type named in §66323(a)(3)(A) — squarely in the pool, subject to the count and the building-standards condition. Two distinctions matter. Tenant storage (rented lockers or cages assigned to existing units) is still “storage” as a space type, but displacing storage a lease promised is a lease question ADU law does not answer — see the common-areas section. And a separate, detached storage building is not “within the portions of existing multifamily dwelling structures”; its route is the ordinance-path accessory-structure conversion in §66314(d)(3), where objective standards may apply. Keep the two routes distinct in an application.

Laundry rooms: the honest answer is “confirm at intake”

Laundry rooms are the one space type where the sources point in two directions, and this guide publishes the tension instead of a conclusion. For conversion: a laundry room is not used for living, sleeping, eating, cooking, or sanitation, so on §66313(e)’s functional test it reads as non-livable space in the same family as the listed boiler and storage rooms, and (a)(3)(A)’s list is non-exhaustive. Against a flat claim: HCD’s Handbook counts laundry rooms inside “livable space” in its size-measurement gloss (“Livable space includes bedrooms, bathrooms, kitchens, laundry rooms, closets, and interior stairs”) — a gloss about measuring a unit’s interior livable space, a different question — and no HCD multifamily text names a laundry room as convertible, while it does name leasing offices, gyms, and enclosed parking. An agency citing the measurement gloss against a laundry conversion is a foreseeable intake dispute. Get the city’s position in writing before designing around a laundry conversion — and if the laundry serves existing tenants, the common-area and lease analysis below applies on top of the entitlement question.

Parking structures and garages: in-structure yes, freestanding by another route

Garages are expressly listed in §66323(a)(3)(A), and HCD’s combinations table lists enclosed parking within the multifamily structure as convertible non-livable space. A parking level inside the existing building is therefore within the (a)(3) frame. A standalone, detached parking structure is not addressed by (a)(3)(A) or the Handbook’s enclosed-parking example on the strict text; its verified route is §66314(d)(3) (conversion of an accessory structure on the same lot, ordinance path). Either way, converting or demolishing the parking creates no replacement-parking obligation (parking section below). Structured parking is also where the building-standards condition bites hardest — ramps, ceiling height, ventilation, and fire separation between parking and new dwellings decide feasibility long after the entitlement is clear.

Fees: Per Unit, With Two Bright Lines

Impact fees are measured per ADU under §66311.5(c)(1): no impact fee may be charged on an ADU of 750 square feet or less of interior livable space; above 750 square feet, impact fees are charged proportionately in relation to the square footage of the primary dwelling unit. (The statute’s “impact fee” excludes utility connection fees and capacity charges, §66311.5(c)(2).) An ADU under 500 square feet is treated as not increasing assessable space for school developer fees (§66311.5(c)(3) and Education Code §17620). The chapter contains no aggregated, per-project fee rule for multifamily ADUs — each unit is measured on its own size. For utility connections, an ADU is not treated as a new residential use for connection-fee and capacity-charge purposes unless it is built concurrently with a new single-family dwelling, and where a separate connection may be required, the charge must be proportionate to the ADU’s burden, by square footage or drainage fixture units upon the water or sewer system (§66311.5(e)), capped by §66013 at the reasonable cost of service. One honest caveat, because it decides real budgets: the no-new-connection shield at §66311.5(d) is written for §66323(a)(1) single-family conversions and JADUs, and whether it extends to §66323(a)(3) multifamily conversions is not settled on the statute’s text — confirm the connection treatment for your conversion units with the serving agency at intake rather than assuming the shield.

Existing Tenants: ADU Law Gives No Right to Displace Anyone

The conversion entitlement reaches only space that is not used as livable space. Nothing in §§66310–66342 — and nothing in the HCD Handbook, which contains no tenant-protection or relocation treatment at all — authorizes demolishing or displacing a tenant-occupied home to build an ADU, and nothing in ADU law requires relocation payments for an ADU project. Tenant protection during a multifamily ADU project comes from general landlord-tenant law, the subject of our California landlord guide; the load-bearing rules are:

• Just cause (Civil Code §1946.2). After 12 months of continuous lawful occupancy, a covered tenancy may be terminated only for a listed just cause. The no-fault cause that matters here is intent to demolish or substantially remodel (§1946.2(b)(2)(D)): “substantially remodel” means permit-required work on structural, electrical, plumbing, or mechanical systems (or hazardous-material abatement) that cannot be done safely with the tenant in place and requires the tenant to vacate for at least 30 consecutive days — cosmetic work does not qualify. The notice must include a copy of the permit (or the signed abatement contract), a description of the work and its duration or the demolition date, and the statutory re-rent language. On any no-fault termination, the tenant is owed one month’s rent in relocation assistance, paid within 15 calendar days of the notice or given as a written waiver of the final month’s rent — failure to pay or waive makes the notice void (§1946.2(d)). Note the asymmetry verified in the landlord guide: the just-cause exemptions name ADUs in the owner-occupied small-property case (§1946.2(e)(5)(A)), while an owner-occupied duplex exemption expressly excludes a duplex where either unit is an ADU or JADU (§1946.2(e)(6)).
• The rent cap (Civil Code §1947.12) — increases capped at 5 percent plus CPI, maximum 10 percent, over 12 months in no more than two increments — has no ADU-named exemption; an older multifamily unit is typically cap-covered, and a newly built ADU is exempt only through the rolling 15-year certificate-of-occupancy exemption, which expires.
• The Ellis Act (Gov. Code §§7060–7060.7) is the withdrawal lane, and it is all-or-nothing: “accommodations” means all dwelling units in the structure (and, for small structures, on the parcel). Ellis is not a step in an ordinary ADU conversion — a non-livable-space conversion displaces no livable unit, so no withdrawal occurs. Do not let anyone sell you an Ellis filing as part of a storage-room conversion.
• The demolition gate (Gov. Code §66300.6). Where a project does demolish dwelling units, the Housing Crisis Act requires the approving city to see at least as many units created, replacement of protected units, advance written notice, and a return right for occupants if demolition does not proceed. Treat §66300.6 as the approval gate to check on any demolition-touching project — not as an ADU entitlement or exemption.
• During construction, entry into occupied units follows Civil Code §1954, and the work may not render an occupied unit uninhabitable (Civil Code §§1941–1941.1; Health and Safety Code §17920.3). More protective local just-cause and rent ordinances control where they apply (§1946.2(i)) — check your city’s ordinance before scheduling any tenant-affecting work.

Common Areas and Open Space: What the Law Does Not Say

Converting shared space is where multifamily ADU projects create their real-world friction — and it is exactly where state ADU law is silent. No provision in §§66310–66342 or the Handbook allocates, preserves, or compensates common areas — laundry rooms, tenant storage, parking areas, courtyards, amenities — when they are converted to ADUs. (The statute does expressly list passageways as convertible space, §66323(a)(3)(A) — subject, like every conversion, to the building’s egress requirements below.) What governs the consequences of taking a shared facility is not ADU law:

• The leases. A facility a lease promised — on-site laundry, assigned storage, a parking space — is a contract and habitability question (Civil Code §§1941–1941.1), and in rent-stabilized cities the loss of a facility can be treated as a reduction in housing services with rent consequences. The entitlement to convert the space is not an entitlement to strip a promised amenity without consequence; price that analysis into the project before filing, with counsel.
• Open space the units consume. Detached ADUs typically land on a courtyard, lawn, or parking court. State law’s only open-space sentences are anti-blocking rules: an agency’s open-space, lot-coverage, floor-area-ratio, front-setback, and minimum-lot-size limits may not be used to prevent an ADU of at least 800 square feet with four-foot side and rear setbacks (§66321(b)(3)), and for §66323 units HCD states that local open-space and landscaping requirements do not apply at all (§66323(b)). There is no replacement, offset, or mitigation rule — no minimum remaining-open-space floor for a multifamily lot adding §66323 units. But §66323(b) binds the agency’s ADU standards; it does not erase private obligations — lease promises, CC&Rs, or a condition in the property’s original entitlement requiring a courtyard. Whether a prior entitlement condition survives is a parcel-specific legal question, not a settled state-law answer.

Density: A Conforming ADU Does Not Exceed It

Two deeming rules, which must be read together, answer the density objection. The ordinance must “provide that accessory dwelling units do not exceed the allowable density for the lot” and are a residential use consistent with the general plan and zoning (§66314(c)) — and a conforming ADU “shall be deemed to be an accessory use … and shall not be considered to exceed the allowable density for the lot” (§66319). HCD’s density FAQ is blunt: “Can an ADU application be denied due to lot density? No.” Section 66314(c) is routinely misquoted as permission to deny; read with §66319 it does the opposite for a conforming unit. For §66323 units the same protection runs through §66323(b): the section contains no density standard, so a local density standard is an unauthorized standard as applied to them. State ADU law sets no maximum units-per-acre and no multifamily density ceiling. One density-bonus nuance (HCD, citing Gov. Code §65915): ADUs can help a project reach the Density Bonus Law’s five-total-units qualification threshold, but ADUs cannot be used to calculate the bonus — the calculation rests on maximum allowable density, which does not include ADUs. Do not underwrite a larger bonus on ADU-inflated density.

Parking Displacement: No Replacement, and Often No Parking at All

The replacement rule is one sentence, and SB 1211 widened it: “When a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced” (§66314(d)(11)). The uncovered-space clause is SB 1211’s 2025 addition. Note the trigger: the demolition must be in conjunction with the ADU construction, or the space converted to an ADU — demolish parking for an unrelated purpose first and claim the bar later, and you are outside the sentence. Around it:

• Where parking may be required at all (the ordinance path), it is capped at one space per ADU or per bedroom, whichever is less, and the spaces may be tandem on a driveway (§66314(d)(10)).
• Zero-parking cases (§66322(a)): no parking standards may be imposed where the ADU is within a half-mile walking distance of public transit; is in an architecturally or historically significant historic district; is part of the proposed or existing primary residence or an accessory structure (the conversion case); sits where on-street permits are required but not offered to the ADU occupant; or has a car-share vehicle within one block. A sixth case — an ADU filed with an application to create a new multifamily dwelling on the same lot — applies only if the parcel also satisfies another listed criterion; do not quote it without that proviso.
• For §66323 units, HCD goes further: local agencies may not impose parking requirements on 66323 Units at all, because §66323 authorizes no parking standard and §66323(b) bars unauthorized ones; guest parking likewise may not be required. We publish that as HCD’s reading of §66323(b); the (d)(10), (d)(11), and §66322 rules above are the statutory text.
• What the chapter does not do: it regulates what the agency may require. It sets no tenant-replacement-parking, notice, or compensation rule for existing tenants whose spaces are displaced — that consequence, if any, lives in the leases and local rent law (see the common-areas section).

Fire Access, Egress, and Sprinklers on a Multifamily Site

Fire access

ADU law sets no fire-access road standard — the four-foot multifamily setback is a zoning setback, not a fire clearance. The standard is the California Fire Code’s: approved fire apparatus access roads for every building hereafter constructed or moved into the jurisdiction, extending to within 150 feet of all portions of the facility and the exterior walls of the first story, measured by an approved route around the exterior (CFC §503.1.1), with an unobstructed width of at least 20 feet and vertical clearance of at least 13 feet 6 inches (§503.2.1); the fire code official may require increased widths, and dead-end turnarounds, grade, and turning radius are set locally. CFC Appendix D dimensions are not statewide law — the appendix applies only where a jurisdiction has adopted it. On a built-out multifamily lot, a detached ADU placed at the back of the parcel is the classic access problem: walk the 150-foot route with the local fire authority before fixing the site plan.

Emergency egress

Multifamily buildings are California Building Code territory, not the residential code’s R310. California deleted the model-code language that limited emergency escape and rescue openings (EEROs): under the State Fire Marshal’s reading (Information Bulletin 20-004), EEROs are required in Group R occupancies generally — basements and sleeping rooms below the fourth story above grade plane need at least one exterior opening into a public way, or a yard or court that opens to one. The size core matches the familiar residential figures: net clear opening at least 5.7 square feet (5.0 square feet at grade floor), clear height at least 24 inches, clear width at least 20 inches, sill no more than 44 inches above the floor, operable from inside without keys or tools. (The EERO section number shifts between code editions, so this guide cites the rule and the dimensions, not an edition-specific section number.) CBC Chapter 10 separately governs the number and arrangement of exits from each story and space — model-code commentary trading EEROs against single-exit allowances does not state California law. For a basement, attic, or parking-level conversion, the EERO and exit analysis is usually the design’s hardest constraint.

Sprinklers: the shield is symmetrical

Section 66323(d) says it expressly for this guide’s buildings: fire sprinklers “shall not be required in an accessory dwelling unit … if sprinklers are not required for the primary residence,” and ADU construction “shall not trigger a requirement for fire sprinklers to be installed in the existing multifamily dwelling” (the ordinance-path parallel is §66314(d)(12)). Read the shield both ways. It stops a city from using your ADU as the trigger to sprinkler the existing building, and from imposing sprinklers the code does not otherwise require for the primary. It does not exempt a new ADU on a building that is already sprinkler-required: HCD’s gloss is that where the primary dwelling is required to have sprinklers, an ADU created on it must be provided with sprinklers too. Independently, CBC §903.2.8 requires an automatic sprinkler system throughout buildings with a Group R fire area — NFPA 13 is the default standard (§903.3.1.1), and NFPA 13R is permitted for Group R only within its story and height limits (for R-2, the highest roof surface less than 45 feet above the lowest level of fire-department vehicle access, §903.3.1.2). The analysis is building-by-building: (1) is the primary sprinkler-required? (2) what does §903 require for the new unit’s building or fire area? (3) which standard — 13, 13R, or 13D — is permitted for it? Local fire amendments sit on top of the state floor.

Utilities on a Shared Site: Capacity, Sewer, Water, and Metering

The plumbing and electrical engineering is covered in depth in our ADU plumbing and utilities guide and electrical and HVAC guide; this section is the multifamily application of those rules.

Capacity is arithmetic, not permission

Drainage is sized by drainage fixture units (CPC Table 702.1 — a 1.6-gpf water closet is 3 DFU, a clothes washer 3, a tub or shower 2, a lavatory 1) checked against the horizontal-branch maximums of CPC Table 703.2 (a 3-inch branch carries 35 DFU; a 4-inch branch 216 — and the table’s water-closet-count notes mean a DFU total alone does not clear a line). Horizontal drainage runs at not less than one-quarter inch per foot; four-inch and larger piping may run at one-eighth inch per foot only where impractical otherwise and with the authority’s approval (CPC §708.1). Water is sized by water supply fixture units (CPC Tables 610.3–610.4, against pressure and developed length), with residual pressure at the most remote fixture of at least 15 psi (CPC §608.1) and a pressure-reducing valve required above 80 psi static (CPC §608.2). Keep the two unit systems separate — a water closet is 3 DFU but 2.5 WSFU, and confusing drainage units with supply units is the classic sizing error on a shared building.

Shared sewer

The plumbing code imposes no ban on reusing an existing building sewer or lateral for added ADUs; reuse turns on the DFU arithmetic above, the line’s condition, and agency approval. Two verified negatives, published because owners are routinely told the opposite: there is no state camera-inspection mandate for tying an ADU into an existing lateral (a camera inspection before tie-in is sound practice, and we recommend it — it is not a code requirement), and there is no statewide lateral-ownership rule — where the owner’s responsibility ends and the agency’s begins is set by the local sewer agency.

Water allocation: no state rule assigns it

No state statute allocates water service between existing tenants and new ADUs on a shared service, and no default payer rule exists. What actually governs is three separate things: the physical capacity (the WSFU arithmetic above); the utility’s meter and service decision (the plumbing code does not size or require water meters — the meter is the water utility’s equipment under its tariffs, and no statewide meter-size chart exists); and who pays, which is set by the leases plus the billing statutes next.

Metering strategy: three different legal objects

Owners conflate three things that the law keeps separate: the utility connection and utility meter (§66311.5 and utility tariffs, above); a private submeter behind a master meter, which ADU law neither requires nor forbids; and billing a tenant from a meter, which is landlord law:

• Gas and electric — disclosure, not a rate cap. Civil Code §1940.9: if service through a tenant’s meter also serves an area outside the unit and the landlord knows it, the landlord must disclose that before the tenancy begins (or on discovery) and either reach a mutual written agreement on payment for the outside-area service or make other mutually agreed written arrangements. A court may order the landlord to become the customer of record and order reimbursement. Section 1940.9 covers gas and electric only — it says nothing about water, and it caps no rate.
• The actual gas/electric rate rule is narrow. Public Utilities Code §739.5 applies only where gas or electric service is provided by a master-meter customer to tenants of an apartment building or similar complex: each user must be charged at the same rate as if receiving service directly, with itemized billing. It does not govern individually utility-metered ADUs, water, or sewer — and ADUs are not named in it.
• Water submeters — Civil Code §§1954.201–1954.219 (SB 7). A submeter must measure only water used within the unit’s exclusive use and control, be type-approved, and be readable by the tenant, with written disclosure before the lease. The tenant’s bill may include only a volumetric charge proportionate to the submeter reading, the tenant’s apportioned share of recurring fixed charges, a permitted late charge, and a billing/administrative fee of the lesser of $4.75 (CPI-adjusted annually from January 1, 2018) or 25 percent of the usage charge (§1954.205(a)). The chapter takes no position on ratio utility billing (RUBS) — RUBS is not banned by it, but RUBS is not submetering, and the two must not be blurred in a lease.
• Installation is a different statute. Water Code §537.1 (SB 7’s installation half) requires measurement of water supplied to each unit — by individual meters or submeters — as a condition of new water service for a newly constructed multiunit structure whose connection application was submitted after January 1, 2018. Existing buildings are not retroactively required to install water submeters; if an owner voluntarily submeters and bills, the §§1954.201–1954.219 billing and disclosure rules apply.

Accessibility: HCD’s Answer Is “Maybe” — Here Is the Real Analysis

ADU law itself imposes no accessibility standard, and the Handbook’s only treatment of the question — may an agency impose accessibility standards on ADUs converted from existing space? — is “Maybe,” with a referral to HCD’s Division of Codes and Standards. The operative analysis is in the building code’s scoping chapters, and it is trigger-based:

• CBC Chapter 11A (privately funded housing) covers all newly constructed covered multifamily dwellings — apartment buildings with three or more dwelling units and condominiums with four or more (§1102A) — plus new common-use areas serving existing covered multifamily dwellings, and additions to existing buildings where the addition alone meets the covered-multifamily definition (§1101A.1). Chapter 11A requires adaptability features, accessible public and common-use areas, and an accessible route — it does not impose a percentage of fully accessible units.
• CBC Chapter 11B (public housing) requires mobility features in 5 percent of units and communication features in 2 percent (§11B-233.3) — a public-funding/ownership lane, not a private apartment lane.
• Federal Fair Housing Act design requirements reach only covered multifamily dwellings designed and constructed for first occupancy after March 13, 1991 (buildings of four or more units: all units in elevator buildings, ground-floor units otherwise), impose seven design requirements with no minimum percentage of fully accessible units, do not cover alterations of pre-1991 buildings — and do cover additions of four or more units.

The synthesis for an existing privately funded property: adding one to eight detached ADUs, or converting non-livable space, does not by that act alone trigger Chapter 11B percentages or Fair Housing design coverage for the existing building. The triggers to check at plan check are whether the new construction is itself a newly constructed covered multifamily dwelling or an addition meeting Chapter 11A’s addition test; whether you are building new common-use areas serving an existing covered dwelling; whether public funding or ownership brings Chapter 11B (and Section 504) in; and whether a leasing office or other public-accommodation area carries its own ADA/Chapter 11B duties.

Managing the Property, and Building Next to Occupied Homes

Property management

There is no state landlord license for renting or managing your own property, and no state rental registry (both verified in the landlord guide; local business licenses and any local registry are ordinance-specific). The licensing line is about managing for others: leasing, soliciting tenants, negotiating leases, and collecting rents for others, for compensation is real estate broker activity (Business and Professions Code §10131(b)), unlawful without a broker’s license (§10130) — with carve-outs that include resident managers of apartment complexes and their employees. Separately, the state’s caretaker regulation (Title 25, §42) requires an apartment house of 16 or more apartments whose owner does not live on the premises to have a manager, janitor, housekeeper, or other responsible person residing on the premises in charge, and a house of more than four but fewer than 16 apartments to post the owner’s or agent’s name and address conspicuously. Whether a permitted ADU counts as an “apartment” toward that 16-unit trigger is not answered in the regulation’s text — a 15-unit building adding one ADU sits exactly on the line, so confirm with counsel rather than assuming either answer.

Construction near occupied units

No ADU statute, Handbook provision, or state code sets construction hours, noise limits, dust controls, or work-sequence rules specific to building ADUs near occupied units. What exists is general law: CBC Chapter 33 safeguards during construction — pedestrian protection scaled to the work’s height and distance from the lot line (construction railings for lower work close to the line; a barrier plus covered walkway for taller work), a walkway in front of every construction site at least four feet wide, railings at least 42 inches and barriers at least eight feet where required, maintained the entire time pedestrians are endangered (§3306). Construction hours are a local ordinance question; there is no statewide construction-hours rule. Habitability and entry law continue throughout (previous sections). Beyond that, the things that make occupied-site construction work — advance written notice to tenants, posted work hours inside the local window, dust control, staging that keeps exits and fire access clear, a named contact for complaints — are practice, labeled as practice here: no primary source makes any of them an ADU requirement, and every experienced multifamily builder treats them as non-optional anyway.

Phasing Multiple ADUs: There Is No State Phasing Rule

Owners ask whether the conversions must come first, or the detached units, or everything at once. The verified answer is a negative: no phasing, sequencing, or staged-occupancy rule for multiple ADUs exists in §§66310–66342 or the Handbook (the Handbook’s full text contains no phasing treatment at all). Section 66323(a) permits the unit types “or any combination” within one ministerial approval — combination is permitted, never required. What actually governs sequencing is permit mechanics:

• Each application is ministerial, without discretionary review or a hearing (§66317(a)(1)), with a written completeness determination within 15 business days (SB 543’s rule, §66317(a)(2)) and a decision within 60 days of a completed application where there is an existing dwelling on the lot — multifamily dwellings are named in that sentence (§66317(a)(3)); silence for 60 days is a deemed approval, and an applicant-requested delay tolls the clock. An appeal of an incompleteness determination or denial is decided within 60 business days (§66317(d)).
• The one sequencing rule in the chapter concerns a proposed primary dwelling: if an ADU application is filed with an application to create a new multifamily dwelling, the agency may delay the ADU decision until it decides the dwelling application — still without discretionary review (§66317(a)(3)). It says nothing about phasing ADUs among themselves.
• Occupancy is per approval: the CBC §110.3 inspection sequence applies to each permitted scope, and no building or portion may be used or occupied before the building official issues its certificate of occupancy (Gov. Code §66328; CBC §111).

Whether a city issues one combined permit or separate permits per phase, and the inspection sign-off order across phases, is local permitting practice — confirm at intake. Sequencing drivers that are real but are project management, not law: doing the utility work once, keeping units occupied and rent-producing during construction, and ordering certificates of occupancy so finished units can be leased while later phases proceed.

A Dated Note on 2027 Law

Two 2026 bills take effect January 1, 2027 and are not current law — they are flagged here only so nobody applies them early. AB 956 (Ch. 791, Stats. 2026) raises the new-construction detached allowance from one to two ADUs on single-family lots only (§66323(a)(2)); it makes no multifamily change in either direction. SB 1117 (Ch. 809, Stats. 2026) changes the above-750-square-foot impact-fee calculation so that, for up to two ADUs on a lot, the proportional fee applies only to the area above 750 square feet — a lot with more than two ADUs stays on the current whole-unit proportional method, which means the 2027 relief will usually not reach a multifamily project. The fee rules in the fees section above are the rules in force today.

Sources: Government Code sections 65915, 66013, 66300.6, 66311.5, 66313, 66314, 66315, 66317, 66319, 66321, 66322, 66323, 66333, 66340–66342, 7060–7060.7; SB 1211 (Skinner), Chapter 296, Statutes of 2024; SB 543, Chapter 520, Statutes of 2025; AB 956, Chapter 791, Statutes of 2026 (effective January 1, 2027); SB 1117, Chapter 809, Statutes of 2026 (effective January 1, 2027); Civil Code sections 1940.9, 1941–1941.1, 1946.2, 1947.12, 1954, 1954.201–1954.219; Water Code section 537.1; Public Utilities Code section 739.5; Business and Professions Code sections 10130–10131; Education Code section 17620; California Code of Regulations, Title 25, section 42; California Building Code chapters 10, 11A, 11B (sections 903.2.8, 903.3.1.1–903.3.1.2, 1101A.1, 1102A, 11B-233.3, 111, 110.3) and chapter 33 (section 3306); California Fire Code section 503; California Plumbing Code sections 608.1–608.2, 708.1 and Tables 610.3–610.4, 702.1, 703.2; California State Fire Marshal Information Bulletin 20-004; 42 U.S.C. section 3604 and 24 CFR section 100.201; HCD Accessory Dwelling Unit Handbook, March 2026 edition (66323 Units and combinations table; Multifamily, Owner-Occupancy, Parking, Fees, Density, and Open Space FAQs; Glossary). Where this guide describes construction or management practice rather than a statute, regulation, or agency guidance, it is labeled as practice in the text; local ordinances and fire-district standards are confirmed with the property’s city and fire authority. This page is part of the California Accessory Dwelling Unit Handbook on this site (Multifamily Properties, Questions 801–850). Related: California ADU Laws · Renting Out Your ADU · ADU Rental Income · ADU Plumbing & Utilities · ADU Fire Sprinkler Requirements · ADU FAQs