Awaiting expert review. This page covers rules that vary by state and local jurisdiction. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
The California Residential Code (CRC) is Part 2.5 of Title 24 of the California Code of Regulations: the state building code for detached one- and two-family dwellings and townhouses, which is the code most ADUs in California are designed under.
The current 2025 edition took effect on 1 January 2026 and is based on the 2024 International Residential Code with California amendments.
Quick facts
- Official name
- California Code of Regulations, Title 24, Part 2.5
- Current edition
- 2025 Triennial Edition 2
- Effective date
- 1 January 2026 2
- Model code
- 2024 International Residential Code (IRC) 3
- Scope (model code)
- Detached one- and two-family dwellings and townhouses up to three stories above grade plane 4
- Energy rules
- In Title 24, Part 6 (the 2025 Energy Code), for permits applied for on or after 1 January 2026 8
- Published by
- California Building Standards Commission 2
Key takeaways
- The CRC is California’s building code for houses. Most ADUs are designed under it.
- The 2025 edition took effect on 1 January 2026 2.
- It is built on a national model code, the 2024 IRC, with California changes 3.
- It covers structure, fire safety, exits and room sizes. Energy, plumbing and electrical rules sit in other parts of Title 24.
- State ADU law limits how the code can be used against an ADU, for example on fire sprinklers 7.
- Your building official decides which code and edition apply to your permit.
What the CRC means, in plain English
A building code is a rule book for safe buildings. It says how strong the frame must be, how people get out in a fire, and how tall a room must be.
California has a whole set of these books, called Title 24. The CRC is the one for houses. It is Part 2.5 of that set.
When an architect draws your ADU, the CRC is the main book they follow. When the city checks the plans, it checks them against the same book. The chart under the edition table shows how that book is made, from the national model code to your permit.
Important distinction
The CRC is California’s version of the IRC, not the IRC itself. California prints its own changes into the text, so a section number or rule in the national IRC can differ from the book your plans follow.
Why the CRC matters to you
The code shapes what you can build and what it costs. Room heights, window sizes and wall ratings all come from it.
If the plans miss a code rule, the city sends back corrections. That adds time and design fees.
Knowing a few basics helps you read a bid or a correction letter. You will also know when to ask your designer a sharper question.
What the CRC is
Every US state uses a building code: the construction law for structure, fire safety, exits, ventilation and the rest. Most adopt model codes from the International Code Council (ICC) and amend them. The ICC’s International Residential Code (IRC) covers houses; its International Building Code covers everything else. General background is in the building code entry.
California publishes its own versions as parts of Title 24 of the California Code of Regulations, adopted every three years. The CRC is Part 2.5. It sits beside the California Building Code (Part 2) and separate parts for electrical, mechanical, plumbing, energy, fire and green building standards.
The CRC is “fully integrated”: California amendments are printed into the IRC text, so one book holds the rules a residential designer uses for structure, fire separation, egress, stairs, ceiling heights and similar items. Energy, plumbing, electrical and mechanical rules are in the other parts of Title 24.
The current edition, and where it came from
| Item | Detail |
|---|---|
| Edition | 2025 California Residential Code (2025 Triennial Edition of Title 24) 2 |
| Published | 1 July 2025 2 |
| Effective | 1 January 2026 2 |
| Based on | 2024 International Residential Code 3 |
| State agency proposing housing amendments | Department of Housing and Community Development (HCD) 3 |
| Next edition | The commission adopts on a three-year cycle; the next edition date was not confirmed for this page |
- ICC publishes the IRCThe 2024 International Residential Code is the starting text 3
- HCD proposes California changesHousing amendments go to the Building Standards Commission 3
- The Commission publishes the CRC2025 edition published 1 July 2025, in effect 1 January 2026 2
- Your city files any local changesOnly with a finding on local climate, geology or terrain
- Your application date locks the editionApplications submitted on or after 1 January 2026 follow the 2025 code 1
The parts of Title 24 an ADU touches
| Part | Name | What it covers |
|---|---|---|
| Part 2 | California Building Code | Buildings other than houses, such as apartments |
| Part 2.5 | California Residential Code | Houses, duplexes, townhouses and most ADUs |
| Part 6 | California Energy Code | Insulation, windows, heating and cooling, solar where required 8 |
| Other parts | Electrical, mechanical, plumbing, fire and green building codes | Wiring, ducts, pipes, fire rules, water and waste |
Which ADUs the CRC governs
The IRC applies to detached one- and two-family dwellings and townhouses not more than three stories above grade plane, and their accessory structures 4. A detached ADU, an attached ADU that makes the house a two-unit dwelling, and most garage conversions fall within that scope, so in California they are designed under the CRC.
An ADU added to an apartment building, or created inside one, generally falls under the California Building Code instead, because the building is not a one- or two-family dwelling. The building official decides which code applies to a given project.
State ADU law adds a protection: Government Code section 66314(d)(8) says local building code requirements for detached dwellings apply, but building an ADU does not by itself count as a Group R occupancy change under the local building code unless the building official makes a written finding based on substantial evidence 6.
Section 66314 was last amended by AB 1170 (Stats. 2025, ch. 67), effective 1 January 2026.
The 2024 IRC includes an optional appendix on ADUs (Appendix BC). In its June 2024 statement of reasons for the 2025 CRC, HCD proposed not to adopt it 3. Confirm the final adopted text before relying on any IRC appendix in California.
How the CRC applies to your ADU, step by step
- Your designer picks the code. For a house lot, that is usually the CRC. The plans list the edition on the cover sheet.
- The edition is set by your application date. Permit applications submitted on or after 1 January 2026 use the 2025 edition of Title 24, energy rules included 1 8. A project applied for by 31 December 2025 generally stays on the 2022 edition.
- The plans show how each rule is met. Structure, fire separation, exits, stairs and room sizes.
- The city checks the plans. Any gaps come back as corrections, cited by section.
- Inspectors check the work. They visit at stages, from foundation to final.
- Final sign-off. The unit can be lived in once it passes.
Small changes during building may need a plan revision before the next inspection.
A few rules you will meet, with their source
| Topic | Rule | Source |
|---|---|---|
| Ceiling height | Living spaces and hallways at least 7 feet; bathrooms and laundry rooms at least 6 feet 8 inches, with exceptions for sloped ceilings | 2024 IRC R313.1 5 |
| Escape openings | Every sleeping room, and basements, need at least one operable emergency escape and rescue opening | 2024 IRC R319.1 5 |
| Fire sprinklers | An ADU or JADU need not have sprinklers if the main home does not need them | Gov. Code § 66323(d) 7 |
| Occupancy change | Building an ADU is not, by itself, a Group R occupancy change unless the official makes a written finding | Gov. Code § 66314(d)(8) 6 |
| Energy | The 2025 Energy Code applies to permits applied for on or after 1 January 2026 | CEC, Title 24 Part 6 8 |
Worked example: a garage conversion meets the code
A hypothetical owner converts a detached garage into a one-bedroom ADU. There are no prices here, just the code checks a designer would walk through.
| Check | What the designer looks at | Typical outcome |
|---|---|---|
| Which code | Detached building on a single-family lot | CRC applies |
| Ceiling height | Garage ceilings must reach the living-space minimum | Raise or keep, depending on the existing frame |
| Bedroom exit | The bedroom needs an escape opening | Add or enlarge a window |
| Sprinklers | Main home has none | Not required for the ADU under state law 7 |
| Energy | Insulation, windows, heating | Meet the 2025 Energy Code if applied for in 2026 8 |
| Fire separation | Wall distance to the property line | Rated wall or fewer openings if close |
Each project is different. The building official makes the final call. See garage conversion research for more.
Where the CRC shows up in an ADU project
- On the cover sheet of the permit drawings, which lists the code editions the design follows.
- In structural design: foundations, framing, seismic and wind bracing.
- In fire separation: rated walls and limited openings near property lines, separate from zoning setbacks.
- In egress and habitability: emergency escape openings, ceiling heights, stairs.
- In plan-check corrections, cited by section number.
Rules outside California
Most states use the IRC for houses too. Many amend it, and many adopt a different edition year. Some let cities choose.
So the same idea, a code for one- and two-family homes, shows up across the country. The details change. Ask your local building department which edition it enforces.
For ADU zoning rules by state, see the state ADU law table.
Code items that drive ADU cost
We do not quote prices here. These are the code items that tend to move a budget. For sourced figures, see ADU cost statistics.
- Fire separation near a property line: rated walls and fewer windows.
- Raising a low ceiling in a garage or basement conversion.
- New or bigger windows for bedroom escape openings.
- Energy code items like insulation, windows and heat pumps 8.
- Foundation and seismic work on an old garage slab.
- Electrical service upgrades; see electrical service research.
Building under the CRC: benefits and limits
Benefits
- One book holds most house rules, so plans are easier to check.
- Lighter than the code for apartment buildings.
- State ADU law blocks some extra local demands, like sprinklers the main home does not need 7.
Limits
- Editions change every three years, so older plans may need updates.
- Local amendments can add rules on top.
- Conversions of old buildings may need costly upgrades to meet it.
The CRC compared with related codes
| Code | Covers | ADU use |
|---|---|---|
| California Residential Code (Part 2.5) | One- and two-family homes, townhouses | Most ADUs on house lots |
| California Building Code (Part 2) | Other buildings, including apartments | ADUs in apartment buildings |
| International Residential Code | National model code for homes | Base text for the CRC 3 |
| California Energy Code (Part 6) | Energy use | Every new ADU 8 |
| Local zoning code | Use, size, height, setbacks | Where the ADU can go, not how it is built |
Misreadings
- Myth An ADU must meet the same code as an apartment building.
- Reality A detached or attached ADU on a single-family lot is usually designed under the CRC, the code for one- and two-family dwellings.
- Myth Title 24 means the energy code.
- Reality Title 24 is the whole building standards code. The energy code is Part 6; the residential code is Part 2.5.
- Myth Permits applied for after 1 January 2026 can use the 2022 edition.
- Reality The edition in force when the application is submitted generally controls; the building department confirms which edition your permit falls under.
What to ask your designer and the city
- Which code and edition will my ADU be checked under?
- Does my city add local amendments to the CRC?
- Is my wall close enough to the property line to need a fire rating?
- Do my bedrooms have code-compliant escape openings?
- Will the ceiling height work in this garage or basement?
- Which energy code path will you use?
- Does the main home need sprinklers? If not, can we skip them in the ADU?
Checklist: code basics for your ADU
- Confirm the code and edition with the building department.
- Check the cover sheet lists the 2025 editions if you apply in 2026.
- Measure ceiling heights in any space you plan to convert.
- Mark every bedroom and check its escape opening.
- Measure the distance from each wall to the property line.
- Ask about energy code needs early, before you pick windows and heating.
- Keep every correction letter and the answer to it.
Related guides and research
Questions about california residential code
What is the current California Residential Code?
The 2025 California Residential Code, Title 24 Part 2.5, published on 1 July 2025 and effective 1 January 2026, according to the California Building Standards Commission. It is based on the 2024 International Residential Code, with California changes printed into the text.
Is an ADU built under the residential code or the building code?
Most California ADUs on single-family lots fall under the California Residential Code, which covers one- and two-family dwellings. ADUs in or added to multifamily buildings generally fall under the California Building Code. The building official decides which applies to your project.
What is the difference between the CRC and the CBC?
The CRC (Part 2.5) covers detached one- and two-family dwellings and townhouses; the CBC (Part 2) covers other buildings, including apartments. Both are parts of Title 24, and both are published by the Building Standards Commission on the same three-year cycle.
Does California use the IRC appendix for ADUs?
HCD proposed not to adopt 2024 IRC Appendix BC (Accessory Dwelling Units) into the 2025 CRC, in its June 2024 statement of reasons 3. Check the adopted code text for the final position before relying on any appendix.
Is Title 24 the same as the energy code?
No. Title 24 is the whole California building standards code. The energy code is Part 6, and the residential code is Part 2.5. People often say “Title 24” when they mean energy rules, so ask which part someone means.
Does an ADU need fire sprinklers in California?
Not if the main home does not need them. Government Code § 66323(d) says sprinklers shall not be required in an ADU or JADU if they are not required for the primary residence 7. Building the ADU also cannot trigger sprinklers in an existing multifamily building.
What ceiling height does an ADU need?
The 2024 IRC, the model for the CRC, sets at least 7 feet for living spaces and hallways and 6 feet 8 inches for bathrooms and laundry rooms, with exceptions for sloped ceilings (R313.1) 5. Confirm the adopted California section with your designer.
Which code edition applies to my ADU permit?
Generally the edition in force when you apply. For energy rules, the Energy Commission says permits applied for on or after 1 January 2026 must meet the 2025 Energy Code 8. Your building department confirms the edition for your permit.
Does an ADU bedroom need an egress window?
Yes, in the model code. The 2024 IRC requires at least one operable emergency escape and rescue opening in every sleeping room and in basements (R319.1) 5. A window is the usual way to meet it. Your plans must show its size and height.
Sources
- California Building Standards Commission, Information Bulletin 25-01 (1 July 2025): 2025 Title 24 publication and effective date, retrieved .
- California Building Standards Commission, Codes: 2025 Triennial Edition of Title 24, retrieved .
- California Building Standards Commission, HCD Initial Statement of Reasons, 2025 California Residential Code (HCD 07/24, 10 June 2024), retrieved .
- International Code Council, 2024 International Residential Code, Section R101.2 Scope, retrieved .
- International Code Council, 2024 International Residential Code, Chapter 3 Building Planning (R313.1 ceiling height; R319.1 emergency escape and rescue openings), retrieved .
- California Legislature, Government Code §66314 (as amended by AB 1170, Stats. 2025, ch. 67), retrieved .
- California Legislature, Government Code §66323(d) (fire sprinklers; as amended by SB 543, Stats. 2025, ch. 520), retrieved .
- California Energy Commission, 2025 Building Energy Efficiency Standards (Title 24, Part 6), retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Edition and effective date from the Building Standards Commission codes page; model-code basis and the Appendix BC proposal from HCD’s statement of reasons; scope, ceiling height and escape openings from the 2024 IRC on codes.iccsafe.org; ADU occupancy and sprinkler rules from Government Code §§66314 and 66323 on leginfo.legislature.ca.gov; energy code applicability from the California Energy Commission; read 7–8 October 2026. The worked example is hypothetical. Held for review (G-REV) before indexing.
Suggest a correction. We fix errors and say what changed.