01 · The standardBS 5839-6 and LACORS, the two documents a fire-alarm spec lives in
A fire-alarm specification for an HMO is written against two documents at once. The technical standard, the British Standard that tells the installer what to do, what to use, and how to prove it works. And the guidance, the LACORS 2008 framework that tells a London licensing officer what they should expect to see in an HMO of a given type.
BS 5839-6:2019+A1:2020 is the Code of Practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises. It is the technical standard. It defines the grades of system (A through F), the detector categorisations (LD1, LD2, LD3 for domestic; L1, L2, L3 for non-domestic / Grade A), the detector types that may be used, the interlinking requirements, the certificate trail, the maintenance schedule and the commissioning tests. It is not itself a statutory instrument, but it is what a competent fire engineer, a council licensing officer and a fire risk assessor will all reference when reviewing the spec.
LACORS 2008 (Housing, Fire Safety) is the non-statutory guidance, published by the Local Authorities Coordinators of Regulatory Services (now the Local Government Group), that tells London councils what minimum spec they should expect to see in each HMO category. LACORS is non-statutory, but in practice it is the operational benchmark. Almost every borough's licensing team uses it, most fire risk assessors draw from it, and any specification that departs from it needs a written rationale under the fire risk assessment to survive challenge. No replacement has been issued in the nearly two decades since it was published; 2026 reality is that LACORS is still how London councils grade HMO fire-alarm adequacy.
Three documents, one spec
A good HMO fire-alarm specification references three documents together: BS 5839-6 for the technical spec, LACORS 2008 for the minimum HMO benchmark, and the fire risk assessment for the risk-led adjustment to either. The FRA is the senior document where there is a conflict; the other two are references. A design certificate that does not cite all three tends to raise licensing-officer eyebrows.
02 · The gradesGrades A through F, what each is, where it fits
BS 5839-6 defines six grades of fire-alarm system for domestic premises. In practice, Grades A and D1 do almost all the work for HMOs; the others are niche. The grade determines the hardware. The category (next section) determines the coverage.
Grade A
Larger / complex HMOsA fully wired fire-alarm system with a dedicated control panel, manual call points at every final exit and on each storey, automatic detectors, separate sounders, and standby batteries sized per BS 5839-1. Grade A follows the non-domestic fire-alarm code BS 5839-1 for the installation methodology. Required for larger or complex HMOs typically on three or more storeys, or with single-staircase escape routes, or with non-shared occupancy patterns that raise the risk rating.
Grade C
Rarely specified nowControl equipment and sounders connected to mains with battery standby; automatic detectors required but manual call points optional. Grade C rarely gets specified in modern HMO work because the gap between Grade D1 (cheaper, code-compliant for most HMOs) and Grade A (fully wired, code-compliant for larger HMOs) leaves little space in the middle. Occasionally specified in legacy upgrades where the original system was Grade C and re-certification is more cost-effective than retro-fitting Grade D1 or Grade A.
Grade D1
HMO defaultMains-powered interconnected smoke and heat alarms with integral sealed tamper-proof lithium battery backup (10-year life). No control panel, no manual call points. This is the default HMO spec for most small and medium shared houses under three storeys. Much cheaper to install than Grade A and substantially less disruptive to the property. The sealed battery is the key upgrade over Grade D2, no replaceable cell means no missed maintenance.
Grade D2
Being phased outMains-powered interconnected smoke and heat alarms with a replaceable battery. Functionally similar to D1 in coverage, but BS 5839-6 now favours sealed batteries for HMOs because landlord-access for battery replacement is unreliable. Most specifiers now default to D1 unless a cost argument forces D2, and the FRA should record the reason. New HMO installations in 2026 should almost always be D1.
Grade F1
Small premises onlyBattery-only interconnected smoke alarms with sealed 10-year lithium battery. No mains supply. Typically specified only for single-household dwellings at the margin, not for HMOs. Where Grade F is occasionally seen in an HMO context it is usually a legacy install that is due for upgrade; LACORS guidance generally prefers mains-powered (Grade D1) for HMOs because of the reliability and tamper-resistance improvement.
Grade F2
Rarely seenBattery-only interconnected smoke alarms with replaceable batteries. Even more tightly constrained than F1 in modern usage. A Grade F2 system in a current HMO is almost certainly an historical hangover awaiting upgrade to D1. The replaceable battery reliability story is poor and licensing officers flag F2 systems on inspection.
The decision tree is simpler than the grade count suggests. For most London HMOs, the choice is between Grade D1 (sealed-battery, mains-powered, interconnected, no panel) and Grade A (full panel-based system with call points, sounders and battery standby). LACORS 2008 sets the threshold between them; a risk-led FRA refines it; a BAFE SP203-1 installer delivers it.
03 · The categoriesCoverage, LD1, LD2, LD3 explained
The grade specifies the hardware. The category specifies how much of the property is covered. BS 5839-6 defines three categories for domestic (Grade D/F) systems, LD1, LD2, LD3, and three matching categories for Grade A systems (L1, L2, L3).
| Category | Coverage | Typical HMO use |
|---|---|---|
| LD1 | Detection in every room in the premises except bathrooms and toilets. The highest residential coverage level. | Higher-risk HMOs, bedsit-style HMOs with locked bedroom doors, 3+ storey HMOs, properties with vulnerable occupants, or where the FRA has flagged specific room-level risks. |
| LD2 | Detection in all circulation areas forming the escape route (hallway, landings, stairs) and in all rooms or areas that present a high fire risk (typically kitchens and living rooms; bedrooms in larger HMOs). | The standard HMO default under LACORS. Appropriate for most 1-3 storey single-unit shared houses. |
| LD3 | Detection only in circulation areas forming the escape route. No room-level detection. | Minimum for single-household dwellings; not usually sufficient for HMOs, though occasionally acceptable for very small two-person lodger arrangements with low FRA risk. |
| L1 / L2 / L3 | Grade A equivalents. Same coverage logic, applied to wired systems tested under BS 5839-1. | Larger HMOs specified as Grade A usually run at L2. L1 is reserved for highest-risk buildings. |
In HMO spec language, a fire-alarm specification is typically written as "Grade X / Category Y". The most common three combinations in London HMO stock: Grade D1 LD2 for standard 1-3 storey shared houses; Grade D1 LD1 for higher-risk bedsit HMOs or properties with specific FRA concerns; Grade A LD2 or Grade A L2 for 3+ storey HMOs and more complex premises. Getting the grade and category right is the entire technical brief.
04 · LACORS defaultsThe LACORS 2008 HMO matrix, what councils expect to see
LACORS 2008 aligns property-type descriptions with recommended grade + category combinations. The table below is the working synthesis that most London licensing officers use as their starting point. It is not statutory, but an FRA that departs from it needs a recorded reason.
| Property type | Typical recommendation | Notes |
|---|---|---|
| Single-household dwelling (family home) | Grade D1 LD3 | Minimum standard. Smoke alarm in hallway + landing, heat alarm in kitchen. Interlinked. |
| Shared house HMO, 1-2 storey, ≤ 6 occupants | Grade D1 LD2 | Smoke alarms in escape route + living room, heat detector in kitchen, optical smoke alarm in each bedroom. Interlinked throughout. |
| Shared house HMO, 3 storeys, ≤ 6 occupants | Grade D1 LD2 (some councils specify Grade A LD2 on the third storey) | Check with licensing officer, third storey can push the spec to Grade A depending on layout. |
| Shared house HMO, 3+ storeys, 7+ occupants | Grade A LD2 or L2 | Panel-based system, call points at final exits and each storey. BAFE SP203-1 installer strongly recommended. |
| Bedsit-style HMO (locked bedroom doors) | Grade A LD1 or Grade D1 LD1 | Locked doors between bedrooms and common escape route require in-room detection. LD1 coverage mandatory. |
| Converted flats within a building of HMOs | Building-wide Grade A L2 system, interlinked between flats | Block-level FRA drives the spec. Cross-reference the Building Safety Act s.156 guide if the building is HRB-qualifying. |
The FRA is the senior document
LACORS is the default, but the fire risk assessment is the authoritative document. If the FRA identifies a specific risk (vulnerable occupant, unusual layout, historic conversion with concealed voids) that elevates the risk above the LACORS benchmark, the spec must follow the FRA, not the table. A spec that matches LACORS but ignores an FRA finding is defensively weak on enforcement.
The question licensing officers actually ask is not "which grade did you fit?", it is "why this grade?". A spec that cites BS 5839-6, references LACORS, and has a matching paragraph in the FRA is a spec that closes the file. A spec without that trail is the one that gets deferred.
05 · DetectorsDetector types, choosing the right sensor for each room
A Grade D1 LD2 system typically uses four detector types, placed according to the fire character of each space.
- Optical smoke alarm. Works by sensing scattered light from smoke particles. Best for smouldering fires in soft furnishings, bedding and furniture. Default for bedrooms, hallways, landings and living rooms. In HMO work, optical is the dominant choice.
- Heat alarm / heat detector. Triggers at a fixed temperature (typically 58°C) or on a rapid rate of rise. Immune to cooking fumes, steam, and the smoke from toasters that plague kitchens. Required in kitchens; occasionally used in drying rooms and garages. A bedroom heat detector is only appropriate in very specific FRA-led cases.
- Ionisation smoke alarm. Senses fast-flaming fires earlier than optical but has a much higher false-alarm rate from cooking and steam. Rarely specified for HMOs now; the trade consensus is that optical outperforms ionisation for residential use across almost all scenarios.
- Carbon monoxide alarm. Separately required under the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 in any room containing a solid-fuel or gas-fired appliance (including gas boilers and gas hobs where the council's interpretation so requires). CO alarms are not smoke detectors, they are a separate system with its own sensor type.
Beyond detector choice, three things matter in every installation: mounting position (ceiling centre, at least 300mm from wall; wall-mounted alarms only where manufacturer-certified and at specified heights), interlinking (so that one alarm triggers all; usually radio-interlinked for D1, hard-wired for Grade A), and test accessibility (every alarm within reach for monthly test-button testing). Any spec that fails on mounting, interlinking or accessibility is a council re-visit waiting to happen.
06 · Worked exampleA 6-bed Peckham HMO, full Grade D1 LD2 specification
2-storey Victorian terrace, converted to 6-bedroom shared house HMO
A 2-storey Victorian terrace in Peckham SE15, converted to a 6-bedroom HMO for working professionals. Ground floor: hallway, shared kitchen, shared living room, one bedroom, bathroom. First floor: five bedrooms, shared bathroom. Single staircase. FRA risk rating moderate. LACORS benchmark: Grade D1 LD2. Here is the full spec.
- Grade D1 mains-powered system with sealed 10-year lithium battery backup throughout. Radio-interlinked to minimise cable runs in the Victorian fabric. All alarms from a single manufacturer family for interconnect compatibility.
- Ground floor · hallway. One optical smoke alarm, ceiling-centre, minimum 300mm from any wall. Test-button reachable from a step.
- Ground floor · kitchen. One heat detector (58°C fixed-temp), mounted ceiling-centre clear of the cooker hood plume. No smoke alarm in the kitchen itself; the hallway smoke alarm covers the door route.
- Ground floor · shared living room. One optical smoke alarm, LD2 adds a detector because the living room is a high fire-risk area (soft furnishings, occupants potentially asleep).
- Ground floor · bedroom. One optical smoke alarm. Mounted centrally. Occupant educated not to cover it.
- First floor · landing. One optical smoke alarm, centre of the landing, clear of the staircase draught.
- First floor · each of the five bedrooms. Optical smoke alarm in each. All radio-interlinked.
- Carbon monoxide alarm. One CO alarm in the kitchen (gas hob); additional CO alarm adjacent to the ground-floor boiler cupboard. Under the Smoke and CO Alarm (Amendment) Regulations 2022.
- Certificates. Design certificate, installation certificate, commissioning certificate, verification certificate, the four-certificate sequence issued on completion, filed with the licensing pack.
- Testing cadence. Weekly test of any one alarm (on rotation), full-system test every six months, third-party verification annually. Tenants given written test instructions at move-in.
£1,200–£1,800
Typical installed cost for a Grade D1 LD2 specification in a 6-bedroom Peckham-style HMO (mains-powered, radio-interlinked, sealed-battery alarms, CO alarms, certificates). Grade A equivalent for the same building would typically be £3,500–£5,500 depending on cable routing and panel specification.
07 · FAQsQuestions HMO landlords keep asking
What is BS 5839-6 and how does it relate to LACORS?
BS 5839-6:2019+A1:2020 is the Code of Practice for the design, installation, commissioning and maintenance of fire detection and fire alarm systems in domestic premises, including HMOs. LACORS 2008 (Housing, Fire Safety) is the non-statutory guidance that London councils apply to set the minimum grade and category for different HMO types. LACORS references BS 5839-6 for the technical spec; councils still use LACORS as their benchmark in 2026 because no replacement has been issued.
What is the difference between Grade A and Grade D1 fire alarms?
Grade A is a fully wired fire-alarm system with a dedicated control panel, manual call points, automatic detectors and sounders, tested to BS 5839-1. Grade D1 is a system of mains-powered interconnected smoke and heat alarms with integral sealed lithium battery backup. Grade A is required for larger or more complex HMOs (typically 3+ storeys or complex layouts). Grade D1 is the standard HMO default for most small-to-medium single-unit HMOs.
What does category LD1, LD2 and LD3 mean?
LD3 provides detection only in the common escape routes (hallway and landings). LD2 extends LD3 to add detection in all rooms or areas that present a high fire risk (typically living rooms, kitchens). LD1 adds detection in every room except bathrooms and toilets. Category L1, L2, L3 are the equivalents for Grade A systems. LACORS HMO defaults generally specify LD2 for most HMOs, with LD1 required for higher-risk property types.
Do I need manual call points in my HMO?
Not for Grade D1 systems, manual call points are not part of a Grade D specification. They are a Grade A feature. A Grade A specification for a larger HMO will include manual call points at all final exits and on each storey. For Grade D1, the automatic-detection network plus interlinked sounders satisfies the alerting duty. A fire risk assessor may recommend voluntary call points where Grade A is not specifically required but the occupancy pattern warrants additional alerting.
What kind of smoke detector should go in each room?
Optical smoke detectors in common parts, hallways and bedrooms; heat detectors in kitchens; CO alarms wherever there is a gas or solid-fuel appliance. Ionisation alarms are rarely specified for HMOs now because of their higher false-alarm rate. Mounting: ceiling centre, at least 300mm from any wall. Interlinked, mains-powered, sealed lithium battery backup.
Who can install and commission an HMO fire alarm?
For Grade D1, any competent electrician qualified to BS 7671 with demonstrable BS 5839-6 experience. For Grade A, a BAFE SP203-1-registered fire-alarm company. Whatever the grade, the installer must issue the full four-certificate sequence: design certificate, installation certificate, commissioning certificate, and verification certificate. That certificate set is what the licensing officer asks to see at HMO licence renewal.
Grade + category spec, BAFE-registered installation, four-certificate pack
HSE designs the fire-alarm system alongside the fire risk assessment, installs to BS 5839-6 for Grade D1 or to BS 5839-1 for Grade A via a BAFE SP203-1-registered partner, and issues the full certificate sequence ready for licensing submission.
08 · Where to go nextTwo practical follow-ups
If HMO compliance is the part of the portfolio you are closest to, these are the two reads that close the loop.
First, the HMO Licensing London Borough-by-Borough Guide, the 22-minute mega-article mapping every London borough's Mandatory / Additional / Selective regime, Article 4 status and current fees. If the fire-alarm spec is step one, the borough licensing picture is step two.
Second, subscribe to The HSE compliance briefing. One email a month with technical fire-safety and licensing updates. When BS 5839-6 or LACORS guidance changes, you will hear it from Kevin within the week.
HSE service for this topic
HMO fire-alarm design & commissioning · fixed-price
From the FRA-led grade decision through install and commissioning to the four-certificate pack ready for your HMO licensing submission, delivered by one team (with a BAFE SP203-1-registered partner for Grade A installs) with one line of accountability.