CRC · California Residential Code
Where are carbon monoxide (CO) alarms required and what are power/interconnect rules?
If your home has any fuel‑burning appliance or an attached garage, put CO alarms outside each sleeping area and on every occupiable level (including basements). If more than one alarm is needed, they must all be interconnected so one alarm triggers them all. When the house has commercial power, alarms should be hardwired with battery backup; limited exceptions apply for older buildings and buildings without commercial power.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
CO alarms are required in dwelling units that contain a fuel‑fired appliance or fireplace, or that have an attached garage that communicates with the dwelling; new alarms are also required when additions or fuel‑burning appliances are added to an existing dwelling. See § R311.2 .
Alarms must be installed outside each separate sleeping area, on every occupiable level (including basements), and inside a bedroom if a fuel‑burning appliance is located there — see § R311.3 .
When more than one CO alarm is required in the same dwelling unit they must be interconnected so that activation of one unit activates all (with limited wireless and existing‑building exceptions) — see § R311.5 .
Primary power must be from the building wiring (commercial source) with a battery backup; limited exceptions allow battery operation in buildings without commercial power and certain existing buildings — see § R311.6 .
Provide CO alarms where a dwelling has a fuel‑burning source or an attached garage: alarms outside each sleeping area and on every occupiable level, hardwired with battery backup, and interconnected when more than one is required. § R311.2, § R311.3, § R311.5, § R311.6
Requirements in detail
1) When CO alarms are required (trigger conditions)
- A CO alarm is required in a dwelling unit if either condition exists:
- The dwelling unit contains a fuel‑fired appliance or fireplace; or
- The dwelling unit has an attached garage with an opening that communicates with the dwelling unit.
(See § R311.2.1 .)
- If an addition is made to an existing dwelling or a fuel‑burning appliance is added where CO alarms were not previously required, new alarms must be installed per Section R311. § R311.2.2 .
2) Where CO alarms must be located
- Install and maintain alarms per the manufacturer’s published instructions, in the following locations:
- Outside each separate sleeping area in the immediate vicinity of the bedrooms.
- On every occupiable level of the dwelling unit, including basements.
- Inside a bedroom if a fuel‑burning appliance is located within that bedroom or its attached bathroom.
(See § R311.3 .)
3) Interconnectivity rules
- If more than one CO alarm is required in an individual dwelling unit, the alarms must be interconnected so that activation of one alarm will activate all alarms in that dwelling unit. § R311.5 .
- Physical interconnection is not required when listed wireless alarms are installed and all alarms sound upon activation of one alarm. § R311.5 .
- Exception for existing buildings built prior to January 1, 2011: interconnection need not be provided under certain limited conditions (see Exceptions in § R311.5). § R311.5 .
4) Power source / wiring rules
- Primary power shall be from the building wiring where that wiring is served from a commercial source; when primary power is interrupted the CO alarm shall receive power from a battery. Wiring must be permanent and without a disconnecting switch other than required for overcurrent protection. § R311.6 .
- Exceptions:
- Battery operation permitted where the building has no commercial power. § R311.6 .
- CO alarms required by alterations/additions per § R311.2.2 may be battery powered. § R311.6 .
- Additional permissions for Group R occupancies and limited existing‑building relief are included in the continuation of § R311.6 (see that section for details). § R311.6 .
Quick decision table
| Decision question | Required action/value | Code Reference |
|---|---|---|
| Does the dwelling contain a fuel‑fired appliance or fireplace? | CO alarm(s) required | § R311.2.1 |
| Does the dwelling have an attached garage that communicates with the dwelling? | CO alarm(s) required | § R311.2.1 |
| Is this an addition or adding a fuel‑burning appliance to an existing dwelling? | Install new CO alarms per R311 | § R311.2.2 |
| Where to place alarms? | Outside each sleeping area, on every occupiable level, in bedroom if appliance in bedroom | § R311.3 |
| Are multiple alarms required? | Alarms must be interconnected (all sound if one activates) | § R311.5 |
| Primary power source | Building wiring (commercial); battery backup required | § R311.6 |
| Existing building built prior to Jan 1, 2011 | Interconnect/power relief may apply (see exceptions) | § R311.5, § R311.6 |
Exceptions & special cases
- Wireless interconnect allowed: Listed wireless CO alarms that cause all required alarms to sound when one activates satisfy the interconnect requirement—no physical wiring required. § R311.5 .
- Existing buildings (pre‑2011) relief: For buildings built prior to January 1, 2011, interconnection and some hardwiring requirements are waived if the work does not remove interior finishes or if access (attic/crawl/basement) is not available, or when the work is limited to certain exterior, plumbing, mechanical or electrical repairs that don’t expose interior finishes. See the listed exception text in § R311.5. § R311.5 .
- No commercial power: Where a building has no commercial electrical service, battery‑operated alarms are permitted. § R311.6 .
- Alterations / additions: When an addition is made or a fuel‑burning appliance is added to an existing dwelling not previously covered, new CO alarms are required; alarms installed under § R311.2.2 may be battery powered per the exceptions in § R311.6. § R311.2.2, § R311.6 .
If you need the exact exception wording (for example to determine whether a particular repair qualifies for the pre‑2011 exception), consult the exception paragraphs in § R311.5 and § R311.6 in the code text.
Common mistakes
- Installing alarms only in bedrooms (instead of outside sleeping areas and on every occupiable level) — check § R311.3 .
- Failing to interconnect multiple required alarms (or relying on non‑listed wireless devices) — see § R311.5 .
- Using plug‑in only devices (without building wiring where commercial power exists) or omitting battery backup — primary power must be building wiring with battery backup per § R311.6 .
- Ignoring manufacturer instructions and listing requirements (alarms must be listed to UL 2034 and installed per the manufacturer) — see § R311.1.1 and § R311.1.2 for listing/installation direction.
Worked example — two‑story single‑family house with attached garage and gas furnace in basement
Scenario facts:
- Two levels above grade + basement (so 3 occupiable levels).
- House has an attached garage that opens into the house.
- Basement contains the gas furnace (fuel‑burning appliance).
- Bedrooms are all on the 2nd floor.
Code application:
- Because the dwelling has both a fuel‑burning appliance and an attached garage, CO alarms are required. § R311.2.1 .
- Location rule requires alarms:
- Outside the bedrooms (2nd floor) in the immediate vicinity of the sleeping area (1 alarm outside sleeping area) — § R311.3(1) .
- On every occupiable level, including the basement → that’s 3 alarms minimum (basement, 1st floor, 2nd floor) — § R311.3(2) .
- No appliance is inside a bedroom, so no requirement to place an alarm inside a bedroom under § R311.3(3). .
- Count: The “outside bedrooms” alarm is on the 2nd floor; plus alarms required for the 1st floor and basement = 3 alarms total. (If the outside‑sleeping‑area alarm happens to be the same device as the 2nd floor occupiable‑level device, you still must meet the location requirements — typically 1 device on that level serving both requirements.) § R311.3 .
- Because more than one CO alarm is required in the dwelling unit, the alarms must be interconnected so activation of one device activates all. Use physical interconnect wiring or listed wireless interconnect that causes all required alarms to sound. § R311.5 .
- Power: Primary power must be from the building wiring (commercial) and alarms must have battery backup; wiring must be permanent with no disconnecting switch (other than overcurrent protection). § R311.6 .
- If this is an existing house built before Jan 1, 2011 and you are doing a minor repair that does not expose interior finishes, the interconnect or hardwire requirement might be waived under the Exceptions in § R311.5 / R311.6 — check the exception text before relying on it. § R311.5, § R311.6 .
Related provisions
- § R311.1.1 — CO alarm listings (UL 2034) and Office of the State Fire Marshal approval requirement.
- § R311.1.2 — Installation per listing and manufacturer’s instructions.
- § R311.4 — Combination CO/smoke alarms permitted in lieu of standalone CO alarms.
- § R311.7 — Carbon monoxide detection systems (NFPA 72 / UL 2075) as an alternative to alarms.
If you need the exact code text for any of these related sections (for permit submittal or plan review), I can pull and quote the precise paragraphs from the code files.
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 2.2 High relevance — show source text
R311.3 Location. Carbon monoxide alarms in dwelling units shall be installed and maintained in accordance with the manufacturer’s published instructions in the following locations: 1. Outside of each separate sleeping area in the immediate vicinity of the bedrooms. 2. On every occupiable level of a dwelling unit, including basements. 3. Where a fuel-burning appliance is located within a bedroom or its attached bathroom, a carbon monoxide alarm shall be installed within the bedroom.
R311.4 Combination alarms. Combination carbon monoxide and smoke alarms shall be permitted to be used in lieu of carbon monoxide alarms.
Combination carbon monoxide/smoke alarms shall comply with Section R311 and all requirements for listing and approval by the Office of the State Fire Marshal for smoke alarms.
R311.5 Interconnectivity. Where more than one carbon monoxide alarm is required to be installed within an individual dwelling unit in accordance with Section R311.3, the alarm devices shall be interconnected in such a manner that the actuation of one alarm will activate all of the alarms in the individual dwelling unit. Physical interconnection of carbon monoxide alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm.
Exception: Interconnection of carbon monoxide alarms in existing buildings built prior to January 1, 2011, shall not be required under any of the following conditions: 1. Where alterations or repairs do not result in removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available that could provide access for interconnection without the removal of interior finishes.
2. No construction is taking place. 3. Repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 4. Work is limited to the installation, alteration or repair of plumbing, mechanical or electrical systems, which do not result in the removal of interior wall or ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required.
R311.6 Power source. Carbon monoxide alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and, where primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than those required for overcurrent protection.
Exceptions:
- Carbon monoxide alarms shall be permitted to be battery operated where installed in buildings without commercial
power. 2. Carbon monoxide alarms installed in accordance with Section R311.2.2 shall be permitted to be battery powered.
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3. Carbon monoxide alarms in Group R occupancies shall be permitted to receive their primary power from other power sources recognized for use by NFPA 72. 4. Carbon monoxide alarms in Group R occupancies shall be permitted to be battery-powered or plug-in with a battery backup in existing buildings built prior to January 1, 2011, under any of the following conditions: 4.1. No construction is taking place. 4.2. Repairs or alterations do not result in the removal of interior wall and ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required. _4.3.
CRC § 18001.8. High relevance — show source text
and the exclusive remedy for the_ failure to comply with this section is an award of actual damages not to exceed one hundred dollars ($100), exclusive of any court costs and attorney’s fees. h. Local ordinances requiring smoke detectors in single-family dwellings may be enacted or amended. However, the ordi- nances shall satisfy the minimum requirements of this section. i. For the purposes of this section, “single-family dwelling” does not include a manufactured home as defined in Section 18007, a mobilehome as defined in Section 18008, or a commercial coach as defined in Section 18001.8.
j. This section shall not apply to the installation of smoke detectors in dwellings intended for human occupancy, as defined in and regulated by Section 13113.7 of the Health and Safety Code, as added by Senate Bill No. 1448 in the 1983-84 Regular Session.
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SECTION R311—CARBON MONOXIDE ALARMS
R311.1 General. Ca rbon monoxide alarms shall comply with Section R311.
R311.1.1 Listings. Carbon monoxide alarms shall be listed and labeled in accordance with UL 2034. Combination carbon monoxide and smoke alarms shall be listed and labeled in accordance with UL 217 and UL 2034.
No person shall install, market, distribute, offer for sale or sell any carbon monoxide device in the State of California unless the device and instructions have been approved and listed by the Office of the State Fire Marshal.
R311.1.2 Installation. Carbon monoxide alarms, and combination carbon monoxide and smoke alarms, shall be installed in accordance with their listing and the manufacturer’s instructions.
R311.2 Where required. Carbon monoxide alarms shall be provided in accordance with Sections R311.2.1 and R311.2.2.
Pursuant to Health and Safety Code Section 17926, carbon monoxide devices shall be installed in all existing dwelling units as required in this section.
R311.2.1 Existing buildings and new construction. For existing buildings and new construction, carbon monoxide alarms shall be provided in dwelling units where either or both of the following conditions exist.
- The dwelling unit contains a fuel-fired appliance or fireplace.
- The dwelling unit has an attached garage with an opening that communicates with the dwelling unit.
R311.2.2 Alterations, repairs and additions. Where an addition is made to an existing dwelling, or a fuel-burning heater, appli- ance or fireplace is added to an existing dwelling, not previously required to be provided with carbon monoxide alarms, new carbon monoxide alarms shall be installed in accordance with Section R311.
Exceptions:
- Work involving the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck.
- Installation, alteration or repairs of plumbing systems.
- Installation, alteration or repairs of mechanical systems that are not fuel fired.
CRC § 915.4 High relevance — show source text
[F] 915.4 Carbon monoxide alarms. Carbon monoxide alarms shall comply with Sections 915.4.1 through 915.4.5 .
[F] 915.4.1 Power source. Carbon monoxide alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source, and when primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than that required for overcurrent protection.
Exception s :
1. Where installed in buildings without commercial power, battery-powered carbon monoxide alarms shall be an acceptable alternative. 2. Carbon monoxide alarms in Group R occupancies shall be permitted to receive their primary power from other power sources recognized for use by NFPA 72. 3. Carbon monoxide alarms in Group R occupancies shall be permitted to be battery-powered or plug-in with a battery backup in existing buildings built prior to January 1, 2011, under any of the following conditions: 3.1. No construction is taking place. 3.2. Repairs or alterations do not result in the removal of interior wall and ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required. 3.3. Repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 3.4. Work is limited to the installation, alteration or repair of plumbing, mechanical or electrical systems, which do not result in the removal of interior wall or ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required.
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[F] 915.4.2 Listings. Residential Carbon monoxide alarms shall be listed in accordance with UL 2034.
No person shall install, market, distribute, offer for sale, or sell any carbon monoxide device in the State of California unless the device and instructions have been approved and listed by the Office of the State Fire Marshal.
[F] 915.4.3 Combination alarms. Combination carbon monoxide/smoke alarms shall be an acceptable alternative to carbon monoxide alarms. Combination carbon monoxide/smoke alarms shall be listed in accordance with UL 217 and UL 2034.
Combination carbon monoxide/smoke alarms shall comply with Section 915, and all requirements for listing and approval by the Office of the State Fire Marshal for smoke alarms.
[F] 915.4.4 Interconnection. Where more than one carbon monoxide alarm is required to be installed within a dwelling unit or within a sleeping unit in Group R occupancies, the alarms shall be interconnected in a manner that activation of one alarm shall activate all of the alarms in the individual unit.
Exception: Interconnection is not required in existing buildings, built prior to January 1, 2011, under any of the following conditions:
1. Physical interconnection is not required where listed wireless alarms are installed and all alarms sound upon activation of one alarm.
CRC § 1.2 High relevance — show source text
No person shall install, market, distribute, offer for sale or sell any carbon monoxide device in the State of California unless the device and instructions have been approved and listed by the Office of the State Fire Marshal.
R311.1.2 Installation. Carbon monoxide alarms, and combination carbon monoxide and smoke alarms, shall be installed in accordance with their listing and the manufacturer’s instructions.
R311.2 Where required. Carbon monoxide alarms shall be provided in accordance with Sections R311.2.1 and R311.2.2.
Pursuant to Health and Safety Code Section 17926, carbon monoxide devices shall be installed in all existing dwelling units as required in this section.
R311.2.1 Existing buildings and new construction. For existing buildings and new construction, carbon monoxide alarms shall be provided in dwelling units where either or both of the following conditions exist.
- The dwelling unit contains a fuel-fired appliance or fireplace.
- The dwelling unit has an attached garage with an opening that communicates with the dwelling unit.
R311.2.2 Alterations, repairs and additions. Where an addition is made to an existing dwelling, or a fuel-burning heater, appli- ance or fireplace is added to an existing dwelling, not previously required to be provided with carbon monoxide alarms, new carbon monoxide alarms shall be installed in accordance with Section R311.
Exceptions:
- Work involving the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck.
- Installation, alteration or repairs of plumbing systems.
- Installation, alteration or repairs of mechanical systems that are not fuel fired.
R311.3 Location. Carbon monoxide alarms in dwelling units shall be installed and maintained in accordance with the manufacturer’s published instructions in the following locations: 1. Outside of each separate sleeping area in the immediate vicinity of the bedrooms. 2. On every occupiable level of a dwelling unit, including basements. 3. Where a fuel-burning appliance is located within a bedroom or its attached bathroom, a carbon monoxide alarm shall be installed within the bedroom.
R311.4 Combination alarms. Combination carbon monoxide and smoke alarms shall be permitted to be used in lieu of carbon monoxide alarms.
Combination carbon monoxide/smoke alarms shall comply with Section R311 and all requirements for listing and approval by the Office of the State Fire Marshal for smoke alarms.
R311.5 Interconnectivity. Where more than one carbon monoxide alarm is required to be installed within an individual dwelling unit in accordance with Section R311.3, the alarm devices shall be interconnected in such a manner that the actuation of one alarm will activate all of the alarms in the individual dwelling unit. Physical interconnection of carbon monoxide alarms shall not be required where listed wireless alarms are installed and all alarms sound upon activation of one alarm.
Exception: Interconnection of carbon monoxide alarms in existing buildings built prior to January 1, 2011, shall not be required under any of the following conditions: 1. Where alterations or repairs do not result in removal of interior wall or ceiling finishes exposing the structure, unless there is an attic, crawl space or basement available that could provide access for interconnection without the removal of interior finishes.
CRC § 304.3.3 High relevance — show source text
304.3.3 Criteria for incidental and minor structural alteration, additions, or repairs of pre-1973 code buildings. [OSHPD 1R, 2, 4 & 5] Provisions of this section shall apply to hospital buildings which were originally designed to pre-1973 building codes, and had no major structural alterations, additions or repairs using 1973 California Building Standards Code or later editions with an OSHPD permit. 1. Nonstructural components. Component importance factor, I p , shall be permitted to be 1.0. Exception: Components required for life safety purposes after an earthquake, including emergency, standby or alternative power systems, mechanical smoke removal systems, fire protection sprinkler systems, fire alarm control panels and egress stairways shall have a component importance factor (I p ) of 1.5.
SECTION 305—IN-SITU LOAD TESTS
[BS] 305.1 General. Where used, in-situ load tests shall be conducted in accordance with Section 1708 of the California Building Code .
SECTION 306—ACCESSIBILITY FOR EXISTING BUILDINGS
[DSA-AC] Public buildings, public accommodations, commercial facilities and public housing regulated by the Division of the State Architect-Access Compliance in Title 24, Part 2, California Building Code, Chapter 1, Section 1.9.1 shall comply with Title 24, Part 2, California Building Code, Chapter 11B.
[HCD 1-AC] Accessibility requirements for covered multifamily dwellings, as defined in Chapter 2 of the California Building Code, are promulgated under HCD authority and are located in Chapter 11A of the California Building Code.
SECTION 307—SMOKE ALARMS
307.1 Smoke alarms. Where an alteration, addition, change of occupancy or relocation of a building is made to an existing building or structure of a Group R and I-1 occupancy, the existing building shall be provided with smoke alarms in accordance with the California Fire Code or Section R310 of the California Residential Code .
Exception: Work classified as Level 1 Alterations in accordance with Chapter 7.
SECTION 308—CARBON MONOXIDE DETECTION
308.1 Carbon monoxide detection. Where an addition, alteration, change of occupancy or relocation of a building is made to an existing building, the existing building shall be provided with carbon monoxide detection in accordance with the California Fire Code or Section R311 of the California Residential Code .
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308.2 Carbon monoxide alarms in existing portions of a building. [HCD 1 & HCD 2] Pursuant to Health and Safety Code Section 17926, carbon monoxide detection shall be provided in all existing Group R buildings, as required in Section 915 of the California Building Code or Section R315 of the California Residential Code, as applicable.
CRC § 2.2 High relevance — show source text
R311.6 Power source. Carbon monoxide alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source and, where primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than those required for overcurrent protection.
Exceptions:
- Carbon monoxide alarms shall be permitted to be battery operated where installed in buildings without commercial
power. 2. Carbon monoxide alarms installed in accordance with Section R311.2.2 shall be permitted to be battery powered.
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3. Carbon monoxide alarms in Group R occupancies shall be permitted to receive their primary power from other power sources recognized for use by NFPA 72. 4. Carbon monoxide alarms in Group R occupancies shall be permitted to be battery-powered or plug-in with a battery backup in existing buildings built prior to January 1, 2011, under any of the following conditions: 4.1. No construction is taking place. 4.2. Repairs or alterations do not result in the removal of interior wall and ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required. 4.3. Repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 4.4. Work is limited to the installation, alteration or repair of plumbing, mechanical or electrical systems, which do not result in the removal of interior wall or ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required.
R311.7 Carbon monoxide detection systems. Carbon monoxide detection systems shall be permitted to be used in lieu of carbon monoxide alarms and shall comply with Sections R311.7.1 through R311.7.4.
R311.7.1 General. Household carbon monoxide detection systems shall comply with NFPA 72. Carbon monoxide detectors shall be listed in accordance with UL 2075.
R311.7.2 Location. Carbon monoxide detectors shall be installed and maintained in the locations specified in Section R311.3 or NFPA 72.
R311.7.3 Permanent fixture. Where a household carbon monoxide detection system is installed, it shall become a permanent fixture of the occupancy and owned by the homeowner.
R311.7.4 Combination detectors. Combination carbon monoxide and smoke detectors installed in carbon monoxide detection systems in lieu of carbon monoxide detectors shall be listed in accordance with UL 268 and UL 2075.
Combination carbon monoxide/smoke detectors shall comply with all requirements for listing and approval by the Office of the State Fire Marshal for smoke alarms.
SECTION R312—MINIMUM ROOM AREAS
R312.1 Minimum area. Habitable rooms shall have a floor area of not less than 70 square feet (6.5 m [2] ).
Exception: Kitchens.
R312.2 Minimum dimensions. Habitable rooms shall be not less than 7 feet (2134 mm) in any horizontal dimension.
Exceptions:
1. Kitchens.
2. Limited-density owner-built rural dwellings. See Section R301.1.1.1.
CRC § 915.3 High relevance — show source text
Exception: Where environmental conditions prohibit the installation of carbon monoxide detector in an enclosed room or space, carbon monoxide detectors shall be installed in an approved enclosed location contiguous with the room or space that contains a CO source.
[F] 915.3 Carbon monoxide detection. Carbon monoxide detection required by Sections 915.1 through 915.2.3 shall be provided by carbon monoxide alarms complying with Section 915.4 or carbon monoxide detection systems complying with Section 915.5.
[F] 915.3.1 Alarm limitations. Carbon monoxide alarms shall only be installed in dwelling units and in sleeping units. They shall not be installed in locations where the code requires carbon monoxide detectors to be used.
[F] 915.3.2 Fire alarm system required. New buildings that are required by Section 907.2 to have a fire alarm system and by Section 915.2 to have carbon monoxide detectors shall be connected to the fire alarm system in accordance with NFPA 72.
[F] 915.3.3 Fire alarm systems not required. In new buildings that are not required by Section 907.2 to have a fire alarm system, carbon monoxide detection shall be provided by one of the following:
- Carbon monoxide detectors connected to an approved carbon monoxide detection system in accordance with NFPA 72.
- Carbon monoxide detectors connected to an approved combination system in accordance with NFPA 72.
- Carbon monoxide detectors connected to an approved fire alarm system in accordance with NFPA 72.
- Where approved by the fire code official, carbon monoxide alarms maintained in accordance with the manufacturer’s instructions.
[F] 915.3.4 Installation. Carbon monoxide detection shall be installed in accordance with NFPA 72 and the manufacturer’s instructions.
[F] 915.4 Carbon monoxide alarms. Carbon monoxide alarms shall comply with Sections 915.4.1 through 915.4.5 .
[F] 915.4.1 Power source. Carbon monoxide alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source, and when primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than that required for overcurrent protection.
Exception s :
1. Where installed in buildings without commercial power, battery-powered carbon monoxide alarms shall be an acceptable alternative. 2. Carbon monoxide alarms in Group R occupancies shall be permitted to receive their primary power from other power sources recognized for use by NFPA 72. 3. Carbon monoxide alarms in Group R occupancies shall be permitted to be battery-powered or plug-in with a battery backup in existing buildings built prior to January 1, 2011, under any of the following conditions: 3.1. No construction is taking place. 3.2. Repairs or alterations do not result in the removal of interior wall and ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required. 3.3. Repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 3.4. Work is limited to the installation, alteration or repair of plumbing, mechanical or electrical systems, which do not result in the removal of interior wall or ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required.
CRC § 915.3.1 High relevance — show source text
915.3.1 Alarm limitations. Carbon monoxide alarms shall only be installed in dwelling units and in sleeping units. They shall not be installed in locations where the code requires carbon monoxide detectors to be used.
915.3.2 Fire alarm system required. New buildings that are required by Section 907.2 to have a fire alarm system and by Section 915.2 to have carbon monoxide detectors shall be connected to the fire alarm system in accordance with NFPA 72.
915.3.3 Fire alarm systems not required. In new buildings that are not required by Section 907.2 to have a fire alarm system, carbon monoxide detection shall be provided by one of the following:
- Carbon monoxide detectors connected to an approved carbon monoxide detection system in accordance with NFPA 72.
- Carbon monoxide detectors connected to an approved combination system in accordance with NFPA 72.
- Carbon monoxide detectors connected to an approved fire alarm system in accordance with NFPA 72.
- Where approved by the fire code official, carbon monoxide alarms maintained in accordance with the manufacturer’s instructions.
915.3.4 Installation. Carbon monoxide detection shall be installed in accordance with NFPA 72 and the manufacturer’s instructions.
915.4 Carbon monoxide alarms. Carbon monoxide alarms shall comply with Sections 915.4.1 through 915.4.4.
915.4.1 Power source. Carbon monoxide alarms shall receive their primary power from the building wiring where such wiring is served from a commercial source, and when primary power is interrupted, shall receive power from a battery. Wiring shall be permanent and without a disconnecting switch other than that required for overcurrent protection.
Exceptions:
1. Where installed in buildings without commercial power, battery-powered carbon monoxide alarms shall be an acceptable alternative. 2. Carbon monoxide alarms in Group R occupancies shall be permitted to receive their primary power from other power sources recognized for use by NFPA 720. 3. Carbon monoxide alarms in Group R occupancies shall be permitted to be battery-powered or plug-in with a battery backup in existing buildings built prior to January 1, 2011, under any of the following conditions: 3.1. No construction is taking place. 3.2. Repairs or alterations do not result in the removal of interior wall and ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required. 3.3. Repairs or alterations are limited to the exterior surfaces of dwellings, such as the replacement of roofing or siding, or the addition or replacement of windows or doors, or the addition of a porch or deck. 3.4. Work is limited to the installation, alteration or repair of plumbing, mechanical or electrical systems, which do not result in the removal of interior wall or ceiling finishes exposing the structure in areas/spaces where carbon monoxide alarms are required.
915.4.2 Listings. Residential carbon monoxide alarms shall be listed in accordance with UL 2034.
No person shall install, market, distribute, offer for sale or sell any carbon monoxide device in the State of California unless the device and instructions have been approved and listed by the Office of the State Fire Marshal.
CRC § 18001.8. High relevance — show source text
7. Transfers between spouses resulting from a decree of dissolution of a marriage, from a decree of legal separation or from a property settlement agreement incidental to either of those decrees. 8. Transfers by the Controller in the course of administering the Unclaimed Property Law provided for in Chapter 7 (commencing with Section 1500) of Title 10 of Part 3 of the Code of Civil Procedure. 9. Transfers under the provisions of Chapter 7 (commencing with Section 3691) or Chapter 8 (commencing with Section 3771) of Part 6 of Division 1 of the Revenue and Taxation Code. e. No liability shall arise, nor any action be brought or maintained against, any agent of any party to a transfer of title, includ- ing any person or entity acting in the capacity of an escrow, for any error, inaccuracy or omission relating to the disclosure required to be made by a transferor pursuant to this section. However, this subdivision does not apply to a licensee, as defined in Section 10011 of the Business and Professions Code, where the licensee participates in the making of the disclo- sure required to be made pursuant to this section with actual knowledge of the falsity of the disclosure. f. Except as otherwise provided in this section, this section shall not be deemed to create or imply a duty upon a licensee, as defined in Section 10011 of the Business and Professions Code, or upon any agent of any party to a transfer of title, including any person or entity acting in the capacity of an escrow, to monitor or ensure compliance with this section. g. No transfer of title shall be invalidated on the basis of a failure to comply with this section, and the exclusive remedy for the failure to comply with this section is an award of actual damages not to exceed one hundred dollars ($100), exclusive of any court costs and attorney’s fees. h. Local ordinances requiring smoke detectors in single-family dwellings may be enacted or amended. However, the ordi- nances shall satisfy the minimum requirements of this section. i. For the purposes of this section, “single-family dwelling” does not include a manufactured home as defined in Section 18007, a mobilehome as defined in Section 18008, or a commercial coach as defined in Section 18001.8.
j. This section shall not apply to the installation of smoke detectors in dwellings intended for human occupancy, as defined in and regulated by Section 13113.7 of the Health and Safety Code, as added by Senate Bill No. 1448 in the 1983-84 Regular Session.
2025 CALIFORNIA RESIDENTIAL CODE 3-57
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
BUILDING PLANNING
SECTION R311—CARBON MONOXIDE ALARMS
R311.1 General. Ca rbon monoxide alarms shall comply with Section R311.
R311.1.1 Listings. Carbon monoxide alarms shall be listed and labeled in accordance with UL 2034. Combination carbon monoxide and smoke alarms shall be listed and labeled in accordance with UL 217 and UL 2034.
No person shall install, market, distribute, offer for sale or sell any carbon monoxide device in the State of California unless the device and instructions have been approved and listed by the Office of the State Fire Marshal.
CRC § 3-33 High relevance — show source text
R304 Protection of Wood and Wood-Based Products
Against Decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33
R305 Protection Against Subterranean Termites. . . . . . . 3-35
R306 Flood-Resistant Construction. . . . . . . . . . . . . . . . . . . 3-36
R307 Storm Shelters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
R308 Site Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
R309 Automatic Sprinkler Systems . . . . . . . . . . . . . . . . . . . 3-41
R310 Smoke Alarms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
R311 Carbon Monoxide Alarms. . . . . . . . . . . . . . . . . . . . . . . 3-58
R312 Minimum Room Areas . . . . . . . . . . . . . . . . . . . . . . . . . 3-59
R313 Ceiling Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59
R314 Mezzanines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-60
R315 Sleeping Lofts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-60
R316 Habitable Attics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-61
R317 Garages and Carports. . . . . . . . . . . . . . . . . . . . . . . . . . 3-61
R318 Means of Egress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-62
R319 Emergency Escape and Rescue Openings . . . . . . . . 3-65
R320 Handrails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-67
R321 Guards and Window Fall Protection . . . . . . . . . . . . . 3-67
R322 Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-68
R323 Elevators and Platform Lifts . . . . . . . . . . . . . . . . . . . . 3-68
R324 Glazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-68
CRC § 2-5 Medium relevance — show source text
Part II—Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-5
CHAPTER 2 DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . .2-5
R201 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
R202 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Part III—Building Planning and Construction . . . . . . . . . . . .3-5
CHAPTER 3 BUILDING PLANNING . . . . . . . . . . . . . . . . . . . . .3-5
R300 Site Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
R301 Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
R302 Fire-Resistant Construction . . . . . . . . . . . . . . . . . . . . 3-23
R303 Foam Plastic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31
R304 Protection of Wood and Wood-Based Products
Against Decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33
R305 Protection Against Subterranean Termites. . . . . . . 3-35
R306 Flood-Resistant Construction. . . . . . . . . . . . . . . . . . . 3-36
R307 Storm Shelters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
R308 Site Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
R309 Automatic Sprinkler Systems . . . . . . . . . . . . . . . . . . . 3-41
R310 Smoke Alarms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
R311 Carbon Monoxide Alarms. . . . . . . . . . . . . . . . . . . . . . . 3-58
R312 Minimum Room Areas . . . . . . . . . . . . . . . . . . . . . . . . . 3-59
R313 Ceiling Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59
CRC § 7.1 Medium relevance — show source text
_
R311.7 Carbon monoxide detection systems. Carbon monoxide detection systems shall be permitted to be used in lieu of carbon monoxide alarms and shall comply with Sections R311.7.1 through R311.7.4.
R311.7.1 General. Household carbon monoxide detection systems shall comply with NFPA 72. Carbon monoxide detectors shall be listed in accordance with UL 2075.
R311.7.2 Location. Carbon monoxide detectors shall be installed and maintained in the locations specified in Section R311.3 or NFPA 72.
R311.7.3 Permanent fixture. Where a household carbon monoxide detection system is installed, it shall become a permanent fixture of the occupancy and owned by the homeowner.
R311.7.4 Combination detectors. Combination carbon monoxide and smoke detectors installed in carbon monoxide detection systems in lieu of carbon monoxide detectors shall be listed in accordance with UL 268 and UL 2075.
Combination carbon monoxide/smoke detectors shall comply with all requirements for listing and approval by the Office of the State Fire Marshal for smoke alarms.
SECTION R312—MINIMUM ROOM AREAS
R312.1 Minimum area. Habitable rooms shall have a floor area of not less than 70 square feet (6.5 m [2] ).
Exception: Kitchens.
R312.2 Minimum dimensions. Habitable rooms shall be not less than 7 feet (2134 mm) in any horizontal dimension.
Exceptions:
1. Kitchens.
2. Limited-density owner-built rural dwellings. See Section R301.1.1.1.
R312.3 Height effect on room area. Portions of a room with a sloping ceiling measuring less than 5 feet (1524 mm) or a furred ceiling measuring less than 7 feet (2134 mm) from the finished floor to the finished ceiling shall not be considered as contributing to the minimum required habitable area for that room.
SECTION R313—CEILING HEIGHT
R313.1 Minimum height. Habitable space, hallways and portions of basements containing these spaces shall have a ceiling height of not less than 7 feet (2134 mm). Bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).
Exceptions:
- For rooms with sloped ceilings, the required floor area of the room shall have a ceiling height of not less than 5 feet (1524 mm) and not less than 50 percent of the required floor area shall have a ceiling height of not less than 7 feet (2134 mm).
- The ceiling height above bathroom and toilet room fixtures shall be such that the fixture is capable of being used for its intended purpose. A shower or tub equipped with a showerhead shall have a ceiling height of not less than 6 feet 8 inches (2032 mm) above an area of not less than 30 inches (762 mm) by 30 inches (762 mm) at the showerhead.
- Beams, girders, ducts or other obstructions in basements containing habitable space shall be permitted to project to within 6 feet 4 inches (1931 mm) of the finished floor.
- Beams and girders spaced apart not less than 36 inches (914 mm) in clear finished width shall project not more than 78 inches (1981 mm) from the finished floor.
Frequently asked questions
When exactly is an alarm “required” — does a gas range trigger the requirement?
Yes. Any fuel‑burning appliance (which includes gas ranges) in a dwelling unit triggers the CO alarm requirement under § R311.2.1.
Can I use plug‑in CO alarms instead of hardwiring?
Only in limited cases. Where the building has commercial power the primary source must be building wiring with a battery backup per § R311.6; some allowances exist for existing buildings built prior to January 1, 2011 and for buildings without commercial power.
Do CO alarms have to be interconnected with smoke alarms?
The code requires interconnection among CO alarms when more than one CO alarm is required in the dwelling (§ R311.5). Combination CO/smoke alarms are permitted and must meet listing/installation rules; interconnection requirements for combination devices follow the CO alarm interconnect rules in R311.5 and the listing rules.
Are wireless CO alarms acceptable for interconnect?
Yes — listed wireless alarms that cause all required alarms to sound when one activates are allowed in place of physical interconnection (§ R311.5). Ensure the wireless system is listed.
If I add a gas water heater during a remodel, do I have to add CO alarms?
Yes — when a fuel‑burning appliance is added to an existing dwelling where alarms weren’t previously required, new CO alarms must be installed in accordance with Section R311 (§ R311.2.2).
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