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Chapter 3 — BUILDING PLANNING

Section R311 — CARBON MONOXIDE ALARMS

2025 California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-07-29 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

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.

  1. The dwelling unit contains a fuel-fired appliance or fireplace.
  2. 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:

  1. 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.
  2. Installation, alteration or repairs of plumbing systems.
  3. 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.

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:

  1. 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.

3-58 2025 CALIFORNIA RESIDENTIAL CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

BUILDING PLANNING

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.

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▸ Contents — 2025 California Residential Code (Title 24, Part 2.5)
2025 California Residential Code (Title 24, Part 2.5)
  1. Chapter 1 — ADMINISTRATION
  2. Chapter 2 — DEFINITIONS
  3. ▸ Chapter 3 — BUILDING PLANNING
    Overview
    1. Section R300 — SITE DRAINAGE
    2. Section R301 — DESIGN CRITERIA
    3. Section R302 — FIRE-RESISTANT CONSTRUCTION
    4. Section R303 — FOAM PLASTIC
    5. Section R304 — PROTECTION OF WOOD AND WOOD-BASED PRODUCTS AGAI…
    6. Section R305 — PROTECTION AGAINST SUBTERRANEAN TERMITES
    7. Section R306 — FLOOD-RESISTANT CONSTRUCTION
    8. Section R307 — STORM SHELTERS
    9. Section R308 — SITE ADDRESS
    10. Section R309 — AUTOMATIC SPRINKLER SYSTEMS
    11. Section R310 — SMOKE ALARMS
    12. Section R311 — CARBON MONOXIDE ALARMS
    13. Section R312 — MINIMUM ROOM AREAS
    14. Section R313 — CEILING HEIGHT
    15. Section R314 — MEZZANINES
    16. Section R315 — SLEEPING LOFTS
    17. Section R316 — HABITABLE ATTICS
    18. Section R317 — GARAGES AND CARPORTS
    19. Section R318 — MEANS OF EGRESS
    20. Section R319 — EMERGENCY ESCAPE AND RESCUE OPENINGS
    21. Section R320 — HANDRAILS
    22. Section R321 — GUARDS AND WINDOW FALL PROTECTION
    23. Section R322 — ACCESSIBILITY
    24. Section R323 — ELEVATORS AND PLATFORM LIFTS
    25. Section R324 — GLAZING
    26. Section R325 — LIGHT, VENTILATION AND HEATING
    27. Section R326 — SANITATION
    28. Section R327 — TOILET, BATH AND SHOWER SPACES
    29. Section R328 — AGING-IN-PLACE DESIGN AND FALL PREVENTION
    30. Section R329 — SOLAR ENERGY SYSTEMS
    31. Section R330 — ENERGY STORAGE SYSTEMS
    32. Section R331 — STATIONARY ENGINE GENERATORS
    33. Section R332 — STATIONARY FUEL CELL POWER SYSTEMS
    34. Section R333 — RESERVED
    35. Section R334 — CONSTRUCTION WASTE REDUCTION, DISPOSAL AND RECY…
    36. Section R335 — SPECIAL PROVISIONS FOR LICENSED 24-HOUR CARE FA…
    37. Section R336 — LARGE FAMILY DAY-CARE HOMES
    38. Section R337 — MATERIALS AND CONSTRUCTION METHODS FOR EXTERIOR…
    39. Section R338 — ELECTRIC VEHICLE
    40. Section 339 — RESERVED
    41. Section R340 — POLLUTANT CONTROL
  4. Chapter 4 — FOUNDATIONS
  5. Chapter 5 — FLOORS
  6. Chapter 6 — WALL CONSTRUCTION
  7. Chapter 7 — WALL COVERING
  8. Chapter 8 — ROOF-CEILING CONSTRUCTION
  9. Chapter 9 — ROOF ASSEMBLIES
  10. Chapter 10 — CHIMNEYS AND FIREPLACES
  11. Chapter 44 — REFERENCED STANDARDS
  12. Appendix AA — BOARD OF APPEALS
  13. Appendix AB — PERMIT FEES
  14. Appendix AC — RESERVED
  15. Appendix BA — RESERVED
  16. Appendix BB — TINY HOUSES
  17. Appendix BC — RESERVED
  18. Appendix BD — RESERVED
  19. Appendix BE — RADON CONTROL METHODS
  20. Appendix BF — PATIO COVERS
  21. Appendix BG — SOUND TRANSMISSION
  22. Appendix BH — AUTOMATIC VEHICULAR GATES
  23. Appendix BI — LIGHT STRAW-CLAY CONSTRUCTION
  24. Appendix BJ — STRAWBALE CONSTRUCTION
  25. Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)
  26. Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
  27. Appendix BM — 3D-PRINTED BUILDING CONSTRUCTION
  28. Appendix BN — EXTENDED PLATE WALL CONSTRUCTION
  29. Appendix BO — EXISTING BUILDINGS AND STRUCTURES
  30. Appendix CA — RESERVED
  31. Appendix CB — RESERVED
  32. Appendix CC — RESERVED
  33. Appendix CD — RESERVED
  34. Appendix CE — RESERVED
  35. Appendix CF — RESERVED
  36. Appendix CG — NONSEWERED SANITATION SYSTEMS
  37. Appendix CH — PRIVATE SEWAGE DISPOSAL
  38. Appendix CI — SWIMMING POOL SAFETY ACT
  39. Appendix CJ — EMERGENCY HOUSING
  40. Appendix CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL…

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