| Category | Purpose | Description |
|---|---|---|
| Category L1 | Life | Full protection throughout the building — detectors in all areas including roof spaces and floor voids. Provides the earliest possible warning for life safety. Required for high-risk commercial buildings and recommended for HMOs. |
| Category L2 | Life | Detectors covering escape routes and areas of highest fire risk. Balances cost against life-safety benefit for most commercial buildings. |
| Category L3 | Life | Detectors only on escape routes — corridors, stairwells and circulation areas. Provides warning that fire has reached an escape route, giving occupants time to evacuate. |
| Category L4 | Life | Detectors in corridors and circulation areas forming part of the escape route. Minimum life-protection standard for many properties. |
| Category L5 | Life | Detectors installed in a specific area only, typically where a particular fire risk has been identified. The scope is defined by a fire-risk assessment. |
| Category P1 | Property | Full protection throughout the building to detect fire at the earliest possible opportunity — protecting property and business continuity. Typically required by insurers for high-value commercial premises. |
| Category P2 | Property | Detectors in areas of highest fire risk (kitchens, plant rooms, electrical rooms). Balances cost against property protection for lower-risk buildings. |
| Grade D (Domestic) | Domestic | Mains-powered interlinked smoke and heat alarms with tamper-proof battery backup. The legal minimum for domestic properties in England under Building Regulations Part B. Not the same as a full L-category system. |
Which category does my building need?
The category is determined by a fire-risk assessment carried out by a competent person. Factors include occupancy type, number of occupants, means of escape, building height and insurer requirements. Our engineers carry out a no-obligation fire-risk assessment as part of every fire alarm survey.
For domestic properties, a Grade D system (interlinked mains-powered smoke and heat alarms) satisfies Building Regulations Part B for most new-build and refurbishment work. HMOs typically require an L2 or L3 system to satisfy HMO licensing conditions.
Book a Free Fire Alarm Survey
Our engineers will assess your building and recommend the correct BS 5839 category. Free, no-obligation site visit.