CBC 11A vs 11B on a Multifamily Set

Two chapters, two agencies

California writes its accessibility rules into the California Building Code instead of adopting the IBC's Chapter 11, and it writes them twice. Chapter 11A, Housing Accessibility, governs privately funded multifamily housing and is developed by the Department of Housing and Community Development (HCD). Chapter 11B, Accessibility to Public Buildings, Public Accommodations, Commercial Buildings and Public Housing, governs everything its title names and is developed by DSA, a division of the state Department of General Services (DSA, Guide to Public Housing Regulated by Chapter 11B). The local building department enforces both on a project in its jurisdiction.

A multifamily building can fall under one chapter, the other, or both in different parts of the same building. The answer turns on two questions: how the housing is funded, and which spaces in the building serve the public.

The figures below are from the 2025 California Building Code, which took effect on January 1, 2026 and applies to permit applications submitted on or after that date (California Building Standards Commission). A set submitted in 2025 was reviewed under the 2022 edition.

Chapter 11A: covered multifamily dwellings

Chapter 11A applies to newly constructed covered multifamily dwellings. Section 1102A.1 of the 2025 CBC lists them, and the two that matter on most multifamily projects are apartment buildings with three or more dwelling units and condominiums with four or more (2025 CBC 1102A.1). The list also reaches lodging houses, congregate residences, dwellings with three or more of the small studio units the code defines separately, dormitories, homeless shelters and timeshares.

The elevator decides how much of the building is covered. Section 1102A.3 treats multistory units in buildings with and without elevators separately, and it follows the logic of the federal Fair Housing Act, under which every unit in an elevator building of four or more units is covered, and only the ground-floor units in a building without one (DSA guide, Fair Housing Act section). On a podium building with an elevator, that means every unit.

Chapter 11A is an adaptability standard. A covered unit gets an accessible entry and route through the unit, usable kitchens and bathrooms with clear floor space, reinforcement for future grab bars and controls within reach, so a resident can adapt it without rebuilding it.

Chapter 11B: public accommodations and public housing

Chapter 11B applies to public buildings, privately funded public accommodations and commercial facilities, and public housing. For a multifamily practice the last term is the one that decides most projects, and the CBC defines it in Chapter 2:

Public housing is housing constructed or altered by, for, or on behalf of a public entity, or as part of a public entity's program to provide housing, including buildings or complexes with three or more residential dwelling units. The definition's note lists what counts as a public entity's program: local, state or federal financial assistance, Community Development Block Grants, Low Income Housing Tax Credits, the California Multifamily Housing Program, loan agreements and housing bonds. It also lists what does not: density bonuses, and public funds received for energy features, seismic strengthening, water conservation or fire safety.

That paraphrase follows the definition as DSA reproduces it in its public housing guide. Two consequences follow for a typical California pipeline. A tax credit or city-funded affordable building is public housing under 11B. A market-rate building with affordable units earned through the State Density Bonus Law is not public housing on that ground alone, and its units stay under 11A.

Unit counts under 11B

For public housing with residential dwelling units, Section 11B-233.3.1 of the 2025 CBC requires at least 5 percent of the units, and no fewer than one, to have mobility features and to sit on an accessible route, at least 2 percent, and no fewer than one, to have communication features for residents with hearing or vision impairments, and, in buildings with three or more units, adaptable units under Sections 11B-233.3.1.2 and 11B-809.6 (2025 CBC 11B-233.3, UpCodes). The units are dispersed among the unit types. Where a facility has 15 or fewer units, the percentages apply to all the units built under one contract or developed as a whole, whether or not they share a site.

Projects where both chapters apply

Most multifamily buildings in California include some 11B scope even when the housing is private:

Leasing and sales offices. A rental or sales office is a public accommodation, so it, and the route to it, follow 11B even in a privately funded building (CORADA, CBC myths).
Retail and commercial space. Ground-floor retail in a mixed-use building is a commercial facility under 11B, with its own parking, entrances and restrooms.
Publicly funded housing. A public housing project meets 11B for its units and common areas, and Chapter 11A's list of covered buildings names public housing as well. DSA's guidance for a project under more than one standard is to meet each one and, where requirements coincide or conflict, apply the more restrictive (DSA guide).

The federal overlay

The building department reviews the set for the California Building Code only; DSA notes that building officials are not authorized to review for compliance with federal requirements, and that compliance with them rests with the parties who design and develop the project (DSA guide). Two federal rules sit on top of the CBC on many California projects:

The Fair Housing Act applies to covered multifamily dwellings of four or more units first occupied after March 13, 1991, whether the housing is publicly funded or not. Chapters 11A and 11B both provide a way to comply with it.
Section 504 of the Rehabilitation Act applies to any program that receives federal financial assistance, such as a developer receiving HOME or CDBG funds. HUD's Section 504 regulations apply to projects of five or more units and require 5 percent of units with mobility features and an additional 2 percent with communication features, in separate units, dispersed among the unit types.

Both summaries are from the DSA guide, which cites HUD's own Section 504 guidance and the Fair Housing Act Design Manual. Tax credit projects add the accessibility conditions of the California Tax Credit Allocation Committee, which the same guide flags as a separate layer.

Where it shows up on the set

The chapter that governs each space has to be readable from the drawings, because the plan reviewer checks each space for the chapter that governs it.

On the set	What it shows
Code analysis sheet	The funding basis stated, the chapter that governs the units, and the spaces under 11B listed by room
Unit matrix	Every unit by type and floor, marked as 11A covered, 11B mobility, 11B communication, or both, with the percentages computed
Accessible route plans	The site and building routes from parking, the public way and transit stops to every entrance, the leasing office and the common areas
Enlarged unit plans	Each covered unit type with clear floor spaces, turning spaces, door clearances and reach ranges dimensioned; the 11B units drawn as their own plans
Enlarged common area plans	Leasing office, restrooms, mail area, trash rooms, fitness and community rooms, pool and roof deck, each tagged by chapter
Accessibility details	Grab bar reinforcement, counters and sinks, thresholds, signage and the communication features in the 11B units
Parking plans	The accessible stalls counted by chapter, with the route from each stall to the building

The unit matrix is the sheet that saves the most plan check rounds. It turns the percentages into a list of numbered units, and every enlarged plan and every door schedule can be checked with it. On a podium building it sits next to the code analysis in the G series; the multifamily sheet list shows where.

The first question on a new project

Before the first unit plan, ask the owner how the project is financed and whether any of the funding comes through a public program. The answer sets which chapter the units follow, how many 11B units the building needs, and whether Section 504 applies. On a project whose financing changes during design, the matrix is redrawn when it does. For California work generally, see where the studio works in California.

CBC 11A and 11B on a multifamily set