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Building Code Reference

Got a CRC R311.6 correction?

CO alarm power source

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CRC R311.6 requires carbon monoxide alarms in residential buildings to be powered by the building's electrical wiring with battery backup where that wiring is served from a commercial power source. Combination smoke and CO alarms that meet both standards are permitted in place of separate units. Most single-family, ADU, and remodel permits in California that involve sleeping rooms or fuel-burning appliances will get flagged under R311.6 if the plans don't specify the alarm power type.

How to fix it

  1. Add a CO alarm power-source note to the electrical schedule

    On your electrical or general notes sheet, add a line: "Carbon monoxide alarms: 120V AC hardwired with battery backup per CRC R311.6." If you're using a combination smoke/CO alarm, call that out explicitly: "Combination smoke/CO alarm: listed to both UL 217 and UL 2034, 120V AC hardwired with battery backup." This note is the first thing a plan-checker looks for. Without it, the schedule is incomplete regardless of what the floor plan shows.

  2. Show alarm locations on the floor plan with power-type callouts

    Mark each CO alarm (or combination alarm) symbol on the floor plan. Next to each symbol, note the power type: "HW" for hardwired or annotate with a legend that defines HW as 120V AC/battery backup. For fuel-burning appliances added by the permit (furnace, water heater, range, fireplace insert), confirm alarms are shown on every occupiable level and outside each separate sleeping area in the immediate vicinity of the bedrooms. If your jurisdiction uses a specific alarm-placement diagram, include it or reference it.

  3. Confirm new circuits on the electrical riser or panel schedule

    If the project includes a new panel, sub-panel, or any new branch circuits, add CO alarm circuits to the panel schedule. Labeling a breaker "CO/Smoke Alarm" ties the electrical plan to the alarm schedule and removes any ambiguity about power source. Reviewers cross-check the panel schedule against the floor plan. A hardwired alarm shown on the floor plan with no corresponding circuit in the panel is another common flag.

  4. Document the battery backup requirement

    Hardwired with battery backup is the default requirement. The battery backup keeps the alarm operational during a power outage. Your plans don't need to specify the battery chemistry, but a note like "with integral battery backup per R311.6" satisfies the reviewer. If you're installing sealed (10-year) lithium battery-only alarms under an R311.6 exception, such as alarms added under R311.2.2 for an addition or a newly added fuel-burning appliance, or a building without commercial power, cite that exception on the plans. Otherwise the plan-checker will expect hardwired alarms and reject the battery-only spec.

  5. Check combination alarm listing requirements

    If you're using a combination smoke and CO alarm to satisfy both R310 (smoke) and R311 (CO), confirm the product is listed to both UL 217 (smoke) and UL 2034 (CO). Most major manufacturers ship combination units that are dual-listed. Add the listing reference to your general notes: "Combination alarms listed per UL 217 and UL 2034." Plan-checkers see this enough that they'll look for it. Missing the dual-listing call-out generates a follow-up even if the product itself would pass.

  6. Reconcile the mechanical sheet with the alarm schedule

    If your permit includes a new or relocated fuel-burning appliance — furnace replacement, tankless water heater, gas fireplace insert — make sure the mechanical sheet references the CO alarm placement. A note on the mechanical sheet like "CO alarm locations per electrical floor plan" ties the two sheets together. When the plan-checker reviews the mechanical scope and finds a new furnace but sees no corresponding alarm update, that's an automatic R311.3/R311.6 flag. Cross-referencing closes that gap.

  7. Resubmit with a revision cloud on every changed sheet

    When you resubmit after an R311.6 correction, cloud the changes on each sheet: the floor plan where alarm symbols were added or annotated, the electrical schedule where the power-type note was added, and the panel schedule if circuits were added. Include a revision delta note ("Rev 1: CO alarm power source per R311.6") in the title block. Revision clouds speed up the review because the plan-checker goes directly to the changes rather than re-checking the whole set.

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Why you got flagged

Plan-checkers cite R311.6 most often when the plans call out CO alarms but don't specify how they're powered. A note that just says "CO alarms per code" on the schedule doesn't tell the reviewer whether the alarms are plug-in, hardwired, or battery-only. Battery-only units satisfy R311.6 only under its listed exceptions, such as no commercial power, alarms added under R311.2.2, or certain buildings built before 2011. The plans need to document the exception, not assume it.

A second common trigger is new ADU permits. A new detached ADU is new construction with commercial power, so the battery-only exceptions don't apply — hardwired with battery backup is required. Plans that show standalone battery-operated CO alarms on the ADU unit get flagged every time, because the plan-checker can see there's a new panel and new circuits in the same set.

Remodel permits that add a fuel-burning appliance — a gas range, a furnace, a tankless water heater — also pull in R311.6. The alarm network has to cover the new appliance zone, and if the remodel touches wiring, the revised plans need to confirm the alarm is hardwired. Showing the appliance on the mechanical sheet without updating the electrical or alarm schedule is what gets the correction.

A fourth scenario: combination smoke/CO alarms specified correctly in the schedule, but shown as battery-only on the electrical plan. The contradiction between the schedule and the electrical drawing flags the set for inconsistency, and R311.6 is the citation that sticks.

The official code

California Residential Code — Building Standards Commission adopted code

Read the source →

Common questions

Can I use battery-only CO alarms in a new ADU under CRC R311.6?
Not for a new detached ADU on commercial power. CRC R311.6 requires CO alarms to take primary power from building wiring served from a commercial source, with battery backup. The battery-only exceptions cover buildings without commercial power, alarms installed under R311.2.2 (an addition or a newly added fuel-burning appliance in an existing dwelling), and certain pre-2011 buildings. An attached ADU built as an addition may qualify under R311.2.2, so cite the exception if you use it. If you spec battery-only in a fully wired ADU, expect an R311.6 correction on first review.
Does a combination smoke/CO alarm satisfy both R310 and R311.6?
Yes, a combination alarm that is listed to both UL 217 (smoke) and UL 2034 (carbon monoxide) satisfies both CRC R310 and R311.6. The combination unit still has to be hardwired with battery backup where wiring is available. The advantage is you're placing fewer devices and reducing wiring runs. Most major alarm brands ship dual-listed combination units. Call out the dual listing explicitly in your general notes — "combination smoke/CO alarms listed per UL 217 and UL 2034" — or the plan-checker will ask for clarification.
When does R311.6 allow battery-only CO alarms?
R311.6 does not use a "wiring near the location" test. The baseline is primary power from building wiring served from a commercial source, with battery backup. Battery-only alarms are allowed in buildings without commercial power, for alarms installed under R311.2.2 (an addition, or a fuel-burning appliance or fireplace added to an existing dwelling), and in Group R buildings built before January 1, 2011 under the listed conditions. Document the exception in the plans if you're claiming it: name the exception and the scope that qualifies.
Does a water heater replacement trigger R311.6?
It can, depending on the scope. If you're replacing a gas water heater under a standalone mechanical permit and the plans add or relocate CO alarms, R311.6 applies to the power specification of those alarms. Under CRC R311.2, a gas water heater is a fuel-burning appliance that requires CO alarm coverage. If the permit is limited to the appliance swap and no existing alarms are moved, many jurisdictions don't require upgrading existing wired alarms. But if the plans show new alarm placement, those alarms must meet R311.6. Check with your local building department on the specific scope threshold.
Do CO alarms need to be interconnected under R311.6?
Interconnection is not required specifically by R311.6, which focuses on power source. Interconnection comes from R311.5, which requires it where more than one CO alarm is required. That said, if you're hardwiring CO alarms anyway, interconnecting them is straightforward and adds redundancy — one alarm detects, all alarms sound. Many plan-checkers will ask about interconnection as a follow-up if the alarm schedule doesn't address it. Cover it in your general notes up front to avoid a second comment: "CO alarms hardwired per R311.6; interconnected per R311.5." Check your jurisdiction's amendments for anything beyond that.
What is the fastest way to clear an R311.6 correction on a resubmit?
Add a clear note to the electrical schedule and the general notes sheet: "CO alarms: 120V AC hardwired with battery backup per CRC R311.6. Combination units listed UL 217/UL 2034 where smoke coverage required." Then cloud that note on resubmit with a revision delta. Also cloud the floor plan anywhere alarm symbols were added or annotated with a power-type callout. Plan-checkers on resubmit go straight to the clouds. If the correction letter cited a specific sheet, make sure that sheet has a cloud. Missing a cloud on an affected sheet sends it back for another round.

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