Jefferson County, MO Building Safety: Carbon Monoxide Detectors (2026)
Key Facts
- Power source
- 120V AC with battery backup
- Interconnection
- Must interconnect with smoke alarms
- Applies to
- New homes and substantial improvements
- Not required for
- Unimproved existing homes
- Governing section
- § 500.400, amending IRC § R315.5
Summary
New homes and substantially improved existing homes in Jefferson County must power carbon monoxide alarms from 120-volt AC wiring with battery backup, interconnected with the home's smoke alarms, under the county's amendment to IRC Section R315.5. The rule applies only to new construction and substantial improvements, not to every existing home.
R315.5. Delete and insert in lieu thereof the following: Power Source. Carbon monoxide alarms shall receive their power from the 120V/AC and interconnected with smoke alarms with battery backup. This shall only apply to a new home or where improvements defined as "substantial improvements" occur.
Full Breakdown
6. The amendment limits when that standard kicks in: it applies only to a new home or to an existing home undergoing what the code defines as a "substantial improvement," so a routine repair or minor remodel of an existing, unimproved home does not trigger a retrofit requirement to add hardwired, interconnected carbon monoxide alarms. 5 circuit during new construction or a qualifying renovation. 350, and a battery-only alarm installed in a covered new home or substantially improved home will not pass that inspection.
Violations & Fines
Installing a battery-only carbon monoxide alarm, or failing to interconnect it with the smoke alarm system, in a new home or a home undergoing a substantial improvement violates Section 500.300 of the Building Code, a misdemeanor punishable by a fine up to one thousand dollars, imprisonment up to one year, or both. The Code Official can withhold final inspection approval under Section 500.350 until the alarm meets the amended R315.5 power and interconnection standard.
Frequently Asked Questions
Do I have to add hardwired CO alarms to my existing Jefferson County home?
Do carbon monoxide alarms have to be wired to the smoke alarms?
Will a battery-only CO alarm pass inspection in a new Jefferson County home?
Sources & Official References
Other rules in Jefferson County
Compare Jefferson County to another location·View the Missouri building safety overview
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