Smoke Alarm Spacing Calculator — BS 5839-6 Compliance

This calculator determines the number of smoke alarms and heat alarms needed based on your property type, number of floors, and room count. It follows the requirements of BS 5839-6 (Fire detection and fire alarm systems for buildings — Code of practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises).

Detection levels (categories)

• LD1: Smoke detection in every room and area (except bathrooms, shower rooms and cupboards under 1m²) plus a heat alarm in the kitchen — required for HMOs and for single dwellings of 4+ storeys
• LD2: Smoke alarms in all circulation spaces (one per storey) plus the principal habitable room (one for the dwelling), with a heat alarm in the kitchen — standard for new builds/rewires under 4 storeys
• LD3: Detection in escape routes (circulation spaces) only — the layout broadly matching the England rented/social statutory minimum

System grades

• Grade A: A control-panel-based system to BS EN 54 with mains power and a standby supply — recommended for single dwellings of 4+ storeys and larger HMOs
• Grade D1: Mains-powered alarms with tamper-proof (sealed) integral battery backup, interlinked — required for new builds and rewires
• Grade D2: Mains-powered alarms with user-replaceable battery backup, interlinked
• Grade F: Battery-only alarms (sealed long-life Grade F1, or user-replaceable Grade F2) — can satisfy the England rented/social statutory minimum, though sealed 10-year units are recommended

Carbon monoxide alarms

The Smoke and Carbon Monoxide Alarm (England) Regulations 2022 (and Approved Document J) require a CO alarm to BS EN 50291 in any room used as living accommodation that contains a fixed combustion appliance — a boiler, gas/oil/solid-fuel heater or log burner — but not a gas cooker. CO alarms are separate from the smoke/heat alarm count.

Regulations

This calculator references BS 5839-6:2019, Approved Document B (Fire safety), Approved Document J, and the Smoke and Carbon Monoxide Alarm (England) Regulations 2015 as amended in 2022. The 2022 Regulations apply to private-rented and social-housing dwellings in England (not owner-occupiers) and require at least one smoke alarm on every storey with living accommodation plus a CO alarm where there is a fixed combustion appliance. In Scotland, since February 2022 every home regardless of tenure must have interlinked alarms (smoke in the main living room, smoke in each circulation space, heat in the kitchen). For HMOs, additional requirements may apply under the Housing Act 2004 and local licensing conditions. Always verify requirements with your local Building Control or Fire and Rescue Service.