· by Michael Blair, Nashville's Electrician
Detector rules are one of the few parts of the code that reach back into existing houses. A permitted renovation, a finished basement or an addition typically requires the whole house to be brought up to the current smoke alarm standard, not just the new rooms. Knowing what that standard is avoids a failed inspection, and it is a good idea whether or not an inspector ever visits.
Where smoke alarms go
The current model codes call for a smoke alarm in every bedroom, one outside each sleeping area in the hallway that serves it, and at least one on every level of the house including a basement. A split-level counts each level. Alarms should be on the ceiling or high on the wall, away from the dead air in a corner and away from the kitchen and bathrooms where cooking and steam cause false trips.
In new work the alarms must be hardwired with battery backup and interconnected, so that when one sounds they all do. That last point is the one older houses miss. A single alarm in a hallway does little for someone asleep behind a closed bedroom door at the other end of the house.
Carbon monoxide alarms
A CO alarm is required where the house has a fuel-burning appliance, a fireplace, or an attached garage, which covers most of Nashville. It goes outside each sleeping area, and a combined smoke and CO unit in the hallway satisfies both requirements in one device.
Gas furnaces, gas water heaters, gas ranges and wood-burning fireplaces are all sources. So is a car running in an attached garage. All-electric houses with no garage and no fireplace are the exception, and they are rarer here than people assume.
- Smoke alarm in each bedroom and in the hall outside
- Smoke alarm on every level, basement included
- CO alarm outside sleeping areas if there is gas, a fireplace or an attached garage
- All interconnected and hardwired in new work
What triggers the current rules in an existing house
Most permitted interior work does. Adding a bedroom, finishing a basement or attic, or a remodel that opens walls will usually require the whole house to meet the smoke alarm standard before the final inspection. Metro Codes decides exactly what applies to a given permit, and asking at plan review is far cheaper than finding out at final.
Where the walls are not open, the code generally allows interconnection by wireless alarms that talk to each other by radio rather than by a run of cable. That makes bringing an older house up to standard a matter of a few devices rather than fishing wire through every ceiling.
Lifespan and the ten-year rule
Smoke alarms have a service life of about ten years, and the sensor degrades whether or not the unit ever sounded. The manufacture date is printed on the back. Anything older than ten years should be replaced regardless of whether it still chirps when tested. CO sensors have their own life, often shorter, also printed on the unit.
Sealed ten-year battery alarms have largely replaced the ones that wanted a fresh nine-volt every year, and for a house that is not being rewired they are the sensible choice. Hardwired units still need their backup battery replaced or, on newer models, come sealed for the life of the unit.