Where every smoke alarm has to go first
Placement starts with the rooms, then the exact spot. Queensland law requires a smoke alarm in every bedroom. On each storey with bedrooms, another alarm goes in the hallway the bedroom doors open onto, or between the bedrooms and the rest of the home if there is no hallway.
A storey with no bedrooms still needs an alarm. It goes on the most likely path someone would take to get out of the house.
Within each of those spaces, the alarm belongs on the ceiling wherever that is practical. If it is not, it can go under an exposed beam no deeper than 300mm. As a last option it can go on a wall, between 100mm and 300mm below the ceiling and more than 300mm from the corner where two walls meet.
The smoke alarm distances that are set in law
Four distances decide where an alarm cannot go. Queensland's Building Fire Safety Regulation sets all four, so they apply to every required alarm, whatever brand it is.
An alarm must be at least 300mm from a light fitting. It must be at least 300mm from the corner where the ceiling meets a wall, because smoke reaches a corner later than the open ceiling. It must be at least 400mm from any opening that blows air from an air conditioner or a ducted system, and at least 400mm from the blades of a ceiling fan. Moving air from either can push smoke past the sensor.
In a stairwell, the alarm cannot sit anywhere something would stop rising smoke from reaching it.
Sloping ceilings need the alarm below the peak
On a sloping or cathedral ceiling, the alarm goes between 500mm and 1,500mm down from the highest point. It does not go at the very top.
You will still find advice online to mount the alarm at the highest point of the room. For a sloping ceiling in Queensland that is wrong. Measure down the slope from the apex and keep the alarm inside that band.
Kitchens, bathrooms and false alarms
Cooking fumes and bathroom steam are two of the most common causes of false alarms, according to the Queensland Fire Department.
The law allows for this. If a required spot is impractical, for example because steam from a bathroom keeps setting the alarm off, the owner can put it somewhere else that still warns the people in the house. The alarm has to stay in the house, in a spot that still warns everyone.
For hardwired alarms, the Queensland Fire Department also says not to put them on a lighting circuit with a dimmer, which can cause false alarms.
What is law and what is advice
Some placement advice you will read is not in Queensland law. Keeping alarms away from windows and out of garages is sensible, and many manufacturers say so in their instructions, but the regulation does not mention either. Follow the instructions that come with the alarm as well as the legal distances.
The 300mm and 400mm distances, the 500mm to 1,500mm band on sloping ceilings and the room-by-room locations are law. Those are the ones an inspection or a sale will be checked against.
How we place alarms on a job
On a smoke alarm job we assess the house first, room by room, against the locations and distances above. Then we install the alarms, replace any old ones and test the full system so every alarm sounds when one is triggered.
Hardwired 240V alarms have to be connected by a licensed electrician, who issues a Certificate of Testing and Compliance for the work. Sealed 10-year battery alarms are different. The owner can fit those, as long as they go in the right places.