Alarm Siting
Correct alarm siting is essential to ensure smoke, heat and carbon monoxide alarms respond quickly and reliably when they are needed. Even the right alarm can fail to provide an effective warning if it is installed in the wrong location.
This page outlines the key siting principles for smoke, heat and carbon monoxide alarms, covering common room layouts and features such as staircases, sloped ceilings and beams. These guidelines apply across different property types and should be followed alongside the relevant British Standards and Building Regulations.
Quick reference: Alarm Siting Essentials
- Site smoke and heat alarms on the ceiling, centrally where possible
- Keep alarms at least 300mm from walls and obstructions
- Install alarms within 3 metres of bedroom doors
- Always use heat alarms in kitchens
- Follow different siting rules for carbon monoxide alarms depending on appliance location
Siting Smoke and Heat Alarms
Here’s everything you need to know about where to put smoke and heat alarms in a property.
- Alarms should be sited on the ceiling, as centrally as possible within the room/area they are installed.
- Site alarms 300mm from walls, light fittings or any obstructions – this is to ensure that they are outside of any ‘dead air’ spaces that occur in corners and spaces where the airflow may be blocked.
- There should be an alarm within 3 metres of every bedroom door to ensure audibility
- Alarms should be positioned between high-risk rooms and bedrooms
- Alarms should not be sited within bathrooms or too close to a bathroom door, as steam and moisture can cause nuisance alarms or damage to the sensors.
- Alarms should be sited on the ceiling, as centrally as possible within the room/area they are installed.
- Site alarms 300mm from walls, light fittings or any obstructions – this is to ensure that they are outside of any ‘dead air’ spaces that occur in corners and spaces where the airflow may be blocked.
- There should be an alarm within 3 metres of every bedroom door to ensure audibility
- Alarms should be positioned between high-risk rooms and bedrooms
- Alarms should not be sited within bathrooms or too close to a bathroom door, as steam and moisture can cause nuisance alarms or damage to the sensors.
Make sure alarms are always installed in line with the relevant British Standards for smoke and heat alarms for domestic properties.
Siting Carbon Monoxide (CO) Alarms
Carbon monoxide alarms have different siting requirements depending on whether they are installed in the same room as a fuel-burning appliance or elsewhere in the property.
If the fuel-burning appliance is in a confined space, for example, a boiler room, then the alarm should be sited on the ceiling just outside the room. If the cupboard is within a bathroom, then our battery-powered carbon monoxide alarms Ei208, Ei208WRF can be installed.
In a room with the fuel-burning appliance:
- Alarms should be sited on the ceiling
- Should be fitted between 1m and 3m from all potential sources of carbon monoxide
- Sited 300mm from walls, light fittings or any obstructions – this is to ensure that they are outside of any ‘dead air’ spaces that occur in corners and spaces where the airflow may be blocked
- If the fuel-burning appliance is in a confined space, for example, a boiler room, then the alarm should be sited on the ceiling just outside the room
In a room without a fuel-burning appliance:
- Alarms should be sited at breathing height. If installed within a bedroom, this could be at the height of the bedhead
Carbon Monoxide Alarm Siting Overview
| Location | Recommended siting |
| Room with a fuel-burning appliance | Ceiling-mounted, 1–3m from appliance |
| Appliance in a cupboard/confined space | Ceiling-mounted just outside the space |
| Room without an appliance | Wall-mounted at breathing height |
| Bedroom | Wall-mounted near bedhead height |
Siting near Staircases, Sloped Ceilings and Beams
If you’re placing a CO, heat, or smoke alarm on a staircase or other difficult-to-reach location, there are a few additional safety steps to consider.
Where to put alarms on staircases
Where stairways are present, site alarms on the flat ceilings at the top and bottom of the stairs. Do not site on the sloped ceiling directly above the stairs.
Where to put alarms on peaked and sloped ceilings
For smoke alarms site a maximum of 600mm vertically down from the apex, for heat alarms a maximum of 150mm vertically down from the apex on the slope. Multi-sensor alarms should also follow the 600mm rule.
Where to put alarms on ceiling beams
For beams with a depth of less than 10% of the room height, site the alarm twice the depth of the beam or 500mm, whichever is less.
If the depth of the beam is more than 10% of the room height, treat the beam as a wall and fit alarms on both sides of the beam.
If the beam is less than 600mm deep, site an alarm securely on the underside of the beam.
Further Information
Alarm siting should always follow the manufacturer’s instructions alongside British Standards and Building Regulations.
For more information, please refer to the British Standard BS 5839-6:2019+A1:2020 for smoke/heat alarms, British Standard BS EN 50292:2013 for carbon monoxide alarms, or the relevant Building Regulations.
You can also contact our Technical Team for advice at technical@aico.co.uk.
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