How Many Smoke Detectors Do I Need?

Minimum Requirements (Building Regulations)

• Every floor level: At least one smoke alarm on each storey (in circulation space)
• Kitchen: Heat alarm (not smoke — cooking causes false alarms)
• Living room with open-plan kitchen: Smoke alarm at least 3m from cooking appliance
• All alarms: Must be interlinked (wired or wireless)
• Principal habitable room: Smoke alarm required on ground floor (England, from 2022)

BS 5839-6 Grades

• Grade F: Battery-only, not interlinked — minimum for existing homes
• Grade D: Mains-powered with battery backup, interlinked — required for new builds and alterations
• Grade C: Central panel system — HMOs and larger buildings
• Grade A/B: Commercial fire alarm systems

Typical House Requirements

For a standard 3-bed, 2-storey house:

• Ground floor hallway: 1 × optical smoke alarm
• First floor landing: 1 × optical smoke alarm
• Kitchen: 1 × heat alarm
• Living room: 1 × smoke alarm (if principal habitable room)
• Total: 3–4 detectors minimum

Detector Types

• Optical (photoelectric): Best for slow, smouldering fires. Use in hallways and bedrooms
• Ionisation: Best for fast-flaming fires. Being phased out due to false alarms
• Heat: Kitchen use only. Fixed temperature (57°C) or rate of rise
• Multi-sensor: Combined optical and heat. Fewer false alarms
• Carbon monoxide: Required in rooms with solid fuel appliances

Positioning

• Ceiling-mounted, at least 300mm from walls
• Away from bathrooms and cooking areas (smoke alarms)
• Within 3m of bedroom doors on the escape route
• Maximum 7.5m from the furthest point in the room

Important Note

These are general guidelines. Always consult Building Control or a fire safety specialist for specific projects. HMOs, flats, and buildings undergoing material change of use have additional requirements under the Fire Safety Order and Building Regulations Part B.