Do You Need an Addressable Fire Alarm for a Block of Flats or HMO
When a fire alarm installer quotes you for an addressable system and someone else quotes for a conventional one, the price difference can be striking. For responsible persons managing flats or HMOs understanding why that difference exists — and which system genuinely fits your building — is one of the more useful things a fire risk assessment can clarify.
If you are not yet familiar with how addressable and conventional systems differ in their basic design, our guide to addressable vs conventional fire alarms covers the fundamentals. This article focuses on the specific question that comes up repeatedly in the buildings we assess: which system is appropriate for a residential block or HMO, and what does the guidance actually say?
The standard that governs fire alarms in residential buildings
Most people familiar with fire alarms in commercial premises will know BS 5839-1, which covers fire detection and alarm systems in non-domestic buildings. Residential buildings — including blocks of flats and HMOs — fall under a different standard: BS 5839-6, which deals specifically with fire detection and alarm systems in domestic premises.
BS 5839-6 is not optional guidance. It is the benchmark against which fire alarm provision in residential buildings is assessed, and a competent fire risk assessor will use it when evaluating whether your current system is appropriate or whether an upgrade is warranted. Understanding its framework helps responsible persons make sense of what they are being asked to install and why.
The standard uses two axes to categorise systems: Grade describes the level of system sophistication, and Category describes the extent of coverage within the property. Grade A is the highest tier, covering a full panel-based fire detection and alarm system — the kind that addressable systems typically represent. Grade D refers to mains-powered units with battery backup that are interlinked but not connected to a central panel. The category classifications run from LD1 (detection throughout, including all rooms where a fire could start) through to LD3 (only in escape routes).
When an installer quotes you for a Grade A system and another quotes for Grade D interlinked detectors, they are not quoting for the same thing. Both may be technically compliant in certain buildings; neither is universally right or wrong. The question is which grade and category is appropriate for your building and occupancy type, and that determination belongs in your fire risk assessment.
Blocks of flats: the stay-put assumption and what it means for your alarm
Most purpose-built flat blocks in the UK operate under a simultaneous evacuation or stay-put strategy, and the choice of strategy has a direct bearing on the kind of alarm system the building needs.
In a stay-put building — typically one with adequate compartmentation, fire-resistant construction, and properly maintained fire doors — the expectation is that residents in unaffected flats remain inside while the fire is contained and dealt with. In these buildings, the fire alarm in the common areas is primarily a tool for alerting occupants that a fire has been detected, prompting those directly affected to leave rather than triggering a building-wide evacuation. A conventional system covering the common parts, combined with domestic smoke alarms within individual flats, can be entirely appropriate in a well-compartmentalised block.
The problem is that many buildings that were originally designed for stay-put are no longer reliably operating on that basis, because the compartmentation that underpins the strategy has degraded over time. Fire doors that have been propped open, replaced with non-compliant alternatives, or left with damaged seals; service penetrations that have not been properly fire-stopped; alterations to layouts that have introduced new risk — all of these erode the logic on which a stay-put strategy depends. When compartmentation cannot be verified, the argument for a more capable detection system strengthens considerably.
The Grenfell Tower fire and the subsequent work of the Building Safety Act 2022 have also changed the regulatory environment for higher-risk residential buildings — those over 18 metres or seven storeys. Responsible persons in those buildings are now subject to additional obligations under the Act, and the expectation from regulators and fire services around detection capability and evacuation management has shifted. For buildings in that category, a conventional system covering common areas may no longer reflect what is genuinely expected, regardless of whether it meets a technical minimum standard.
The key point for flat blocks: a conventional Grade D system in common areas, combined with interlinked domestic detectors inside flats, can be appropriate for a well-maintained, well-compartmentalised purpose-built block operating a stay-put strategy. But "appropriate" depends on the building performing as designed — and that is exactly what a fire risk assessment is there to verify.
HMOs: why the risk profile is genuinely different
HMOs are not simply flats with more occupants. The risk profile of a typical HMO differs from a purpose-built flat block in ways that are relevant to alarm system design, and the guidance reflects this.
Purpose-built flat blocks are designed with fire safety in mind: compartmentation between units, protected escape routes, and a clear relationship between the layout and the strategy for getting people out. A converted HMO — a Victorian terrace split into five or six bedsits, for example — was almost certainly not designed with that logic. The conversion may have introduced risk without introducing the structural protections that would exist in a purpose-built building. Escape routes are often less protected. Fire door provision is frequently poor. The nature of the occupancy — multiple unrelated people, potentially working different hours, with varying familiarity with the building — means that early, precise detection and fast, clear warning matters more.
BS 5839-6 reflects this, and fire risk assessors working on HMOs will generally be looking for a higher category of coverage and, in larger or more complex HMOs, a Grade A system rather than standalone interlinked units. A Grade A addressable system in an HMO gives you detector-level identification — you know exactly which room or corridor the signal is coming from — which is valuable both during an incident and during routine fault-finding. In a larger HMO, the ability to identify which detector has activated without physically inspecting each one in turn is not a luxury; it is a practical necessity for the responsible person.
Larger and licensable HMOs
HMOs that require a licence under the Housing Act 2004 — broadly, those with five or more occupants across two or more households — are subject to licensing conditions that include fire safety requirements. Local housing authorities set those conditions, and they vary, but the expectation in most areas is a Grade A or Grade D system meeting at least Category LD2 coverage, covering escape routes and rooms adjacent to them. A Grade D interlinked system may be acceptable in smaller licensable HMOs; in larger, multi-storey properties the case for Grade A becomes considerably stronger, and some licensing authorities will specify it explicitly.
It is worth noting that "Grade D" and "addressable" are not synonymous. Addressable systems are Grade A by definition — they communicate with a central panel and provide device-level identification. Grade D systems are the standalone battery or mains-powered interlinked detectors that most people associate with domestic smoke alarms. Both can be appropriate in the right building; neither is appropriate in all buildings.
When an addressable system is the right answer
Across the buildings we assess, a Grade A addressable system tends to be the appropriate recommendation in the following situations.
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1Complex or multi-storey layout
In a building where a fire could start on any floor and affect multiple escape routes, knowing that "Zone 2 alarm" is active is considerably less useful than knowing that detector 14 on the third-floor corridor has activated. Addressable systems give the responsible person — and the fire service — that information immediately.
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2Persistent false alarms
False alarms in residential buildings carry real consequences: residents stop taking the alarm seriously, evacuation at night becomes chaotic, and repeated fire service callouts attract enforcement attention. Addressable systems allow sensitivity adjustments at device level, meaning a detector in a kitchen or near a boiler room can be tuned without affecting the rest of the system. That kind of control is not possible with conventional zone-based systems.
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3Evacuation strategy is under review
Buildings that are moving from stay-put to simultaneous evacuation — or where stay-put can no longer be defended because of compartmentation concerns — need a system that supports effective, building-wide response. In those circumstances, common-area conventional detection is unlikely to be adequate, and the fire risk assessment should be reflecting this.
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4Vulnerable or high-dependency residents
Buildings where residents may need assistance to evacuate — whether due to age, disability, or medical need — require Personal Emergency Evacuation Plans (PEEPs) for affected individuals. An addressable system supports PEEP delivery by confirming the location of the incident quickly, which allows staff or wardens to prioritise who needs assistance and where. A zone-only alarm provides much less useful information in those critical first moments.
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5Fire risk assessment identifies system shortcomings
If your fire risk assessment recommends a system upgrade, that recommendation carries legal weight under the Regulatory Reform (Fire Safety) Order 2005. A responsible person who receives that recommendation and does not act on it is not simply leaving a box unticked; they are operating with documented knowledge of a deficiency and no remediation plan. The nature of the recommended upgrade — whether Grade A addressable or an improved Grade D installation — should be specific to the building and clearly justified in the assessment itself.
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6The existing system is obsolete or unsupported
Older conventional systems eventually reach the point where parts are unavailable, maintenance becomes unreliable, and the system as a whole can no longer be demonstrated to meet current expectations. Replacing like-for-like in those circumstances is rarely the right decision, and in many buildings the shift to addressable is as much about future-proofing as about addressing an immediate gap.
When a conventional system may still be acceptable
A conventional or Grade D interlinked system remains appropriate in certain residential buildings, and it would be misleading to suggest otherwise. The relevant factors are the size and simplicity of the building, the reliability of its compartmentation, the nature of the occupancy, and the evacuation strategy.
| Building type | Likely appropriate system | Key conditions |
|---|---|---|
| Small purpose-built flat block (stay-put) | Grade D in flats + conventional Grade A or Grade D in common areas | Compartmentation verified, fire doors maintained, no vulnerable residents |
| Small HMO (3–4 occupants, 2 storeys) | Grade D interlinked LD2 | Compliant with local licensing conditions, good fire door provision |
| Larger HMO (5+ occupants, 3+ storeys) | Grade A addressable | Required in most cases; licensing conditions may specify this explicitly |
| Large or high-rise flat block | Grade A addressable in common areas | Complex layouts, potential evacuation strategy changes, Building Safety Act obligations |
| Converted building (former house or commercial) | Grade A addressable strongly recommended | Compartmentation often unreliable; occupancy risk higher than purpose-built equivalent |
Even in buildings where a conventional system is technically compliant, managing agents and responsible persons increasingly choose addressable systems because the long-term operational advantages — faster fault-finding, fewer engineer callouts, reduced false alarms, clearer maintenance records — outweigh the higher installation cost within a few years.
What a fire risk assessment should tell you
A fire risk assessment that reviews your fire alarm provision should not simply confirm whether a system exists. It should evaluate the system against BS 5839-6, consider whether the grade and category are appropriate for the building and its occupancy, assess the condition and coverage of existing detection, and make a specific recommendation if an upgrade is warranted. If the assessment you have received does not address these points, it may not be providing the level of detail that the building requires.
Our fire risk assessments for residential buildings include a full review of fire alarm provision, covering system grade and category, coverage against BS 5839-6, detector condition and placement, sound level adequacy, and any recommendations linked to the building's evacuation strategy. We are not tied to any installer or manufacturer, which means our recommendations are based on the building rather than on what is convenient to supply.
If you manage a block of flats, a licensed HMO, or a converted residential property in Chester, the Wirral, Cheshire, North Wales, or elsewhere in the North West, and you want an independent view on whether your current fire alarm provision is adequate, please get in touch.
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We carry out fire risk assessments and fire alarm system reviews for residential blocks and HMOs across Chester, the Wirral, Cheshire, North Wales, and the wider North West.
This article provides general guidance only and does not constitute legal or professional advice. Fire safety requirements vary according to building type, age, condition, and occupancy. The guidance above is intended to help responsible persons understand the relevant considerations, not to substitute for a site-specific fire risk assessment. Fletcher Risk Management Ltd accepts no liability for decisions made on the basis of this content. Always consult a competent fire safety professional for advice on your specific property.