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Smoke Alarm Regulations UK: What a Renovation Triggers, Where Alarms Go and the CO Rules
Smoke alarm regulations in the UK depend on what you are doing to the house. Building a new home, converting a loft or making another "material alteration" brings in Approved Document B, which asks for mains-powered smoke alarms with a battery backup, interlinked, in the circulation space on every storey. Fitting a new boiler or wood burner brings in Approved Document J and a carbon monoxide alarm. Letting the property adds a separate set of landlord duties. This page sets out each trigger, where the alarms go, and how to plan them into an interior design so they do not end up stuck in the middle of a feature ceiling.
When building regulations require smoke alarms
There is no law that makes an owner-occupier in England retrofit smoke alarms to a house they are simply living in. The duty arrives with building work. Approved Document B, Volume 1 (dwellings) applies to new homes and to material alterations, which in practice covers loft conversions, many basement conversions and other work that changes the escape route or adds habitable rooms. In those cases the whole dwelling needs a fire detection and alarm system to at least Grade D2 Category LD3 under BS 5839-6.
In plain terms that means:
- Grade D2: mains-powered alarms, each with a standby supply such as a built-in or replaceable battery, so they keep working in a power cut. Alarms should conform to BS EN 14604.
- Category LD3: alarms in the circulation spaces that form the escape route, so the hallway and every landing, on every storey.
- Interlinked: when one alarm sounds, they all sound. Hard-wired or radio interlinks both work.
- Kitchen: where the kitchen is not separated from the stairway or hallway by a door, as in many open-plan layouts, a compatible interlinked heat alarm or heat detector goes in the kitchen.
Grade D2 Category LD3 is the minimum. BS 5839-6 recommends a higher standard for many homes, and adding a smoke alarm in the main living room and a heat alarm in the kitchen even where a door exists is a sensible, cheap upgrade while the ceilings are open. Our pages on loft conversion building regulations, basement conversions and open-plan kitchen fire regulations explain how each project triggers the rule.
Where the alarms go
| Location | Alarm | Notes |
|---|---|---|
| Hallway and every landing | Smoke alarm | The core of an LD3 system; one in each circulation space on each storey |
| Open-plan kitchen with no door to the stairway | Heat alarm | Heat, not smoke, to avoid false alarms from cooking |
| Main living room | Smoke alarm | Recommended upgrade under BS 5839-6, and worth fitting while ceilings are open |
| Room with a boiler, wood burner or open fire | Carbon monoxide alarm | Required when the appliance is installed or replaced |
| Bathroom, shower room | None | Steam causes false alarms; keep alarms out |
Smoke alarms should go on the ceiling, in a position where they are at least 300mm from walls and light fittings, and no alarm should sit where a long stretch of circulation space is left uncovered: Approved Document B asks for one within 7.5m of the door to every habitable room. Keep them away from bathroom doors and directly above the hob, where steam and cooking smoke set them off.
Carbon monoxide alarms: Approved Document J
Since 1 October 2022, Approved Document J has required a carbon monoxide alarm in the room whenever a fixed combustion appliance is newly installed or replaced in a dwelling. That covers gas, oil and solid fuel: boilers, wood burners, gas fires and open fires. Gas cookers are the exception. The alarm should be in the same room as the appliance, usually on the ceiling at least 300mm from any wall, or on a wall above doors and windows and close to the ceiling, and between 1m and 3m horizontally from the appliance. For a wood burner, see our guide to hearth regulations; the installer will normally fit the alarm and record it on the compliance certificate.
If you let the property
Landlords in England have had a separate legal duty since the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 came into force on 1 October 2022. They must fit at least one smoke alarm on each storey with a room used as living accommodation, fit a carbon monoxide alarm in any room used as living accommodation that contains a fixed combustion appliance (gas cookers excluded), and repair or replace alarms once told they are faulty. Councils enforce it and can fine up to £5,000 where a landlord fails to comply with a remedial notice. Battery alarms satisfy the landlord rules, but any building work still needs the Approved Document B standard.
Scotland and Wales
Scotland has stricter rules for all homes, not only rented ones: since February 2022 every home must have interlinked alarms, including a smoke alarm in the living room and on each hallway and landing, a heat alarm in the kitchen, and a carbon monoxide alarm where there is a fixed combustion appliance or flue. Wales applies its own version of the building regulations and, for rented homes, the fitness for human habitation rules under the Renting Homes (Wales) Act. Check the local requirements if your project is outside England.
Designing alarms into the room
Alarms are an afterthought in a surprising number of high-spec renovations, which is how a coffered ceiling or a carefully centred pendant ends up with a white plastic disc beside it. A few things help:
- Plot them on the lighting plan. Alarms, downlights and pendants all compete for the ceiling, and the 300mm clearance from light fittings is easy to forget. Our lighting design basics covers how we lay out a ceiling.
- Choose low-profile models. Slim mains alarms with radio interlink avoid chasing cable between floors in a period house, and some can be painted around or sit in a recessed collar.
- Agree positions before plastering. Mains alarms need a supply, so the electrician must know where they go at first fix.
- Keep the certificate. Building control sign-off for a loft or basement conversion depends on the alarm system, and buyers' solicitors will ask for the paperwork. Electrical work for new alarm circuits falls under Part P.
For the full list of rules that apply to a London renovation, start with our guide to building regulations for renovations, or go back to the Vertigo Interiors home page.
Frequently Asked Questions
Do smoke alarms have to be hard-wired in the UK?
For new homes and material alterations such as loft conversions in England, Approved Document B asks for mains-powered alarms with a standby supply, interlinked, to at least Grade D2 Category LD3. Owner-occupiers who are not doing building work are not required to hard-wire, and battery alarms satisfy the landlord regulations.
Does a loft conversion need interlinked smoke alarms?
Yes. A loft conversion is a material alteration, so the whole house needs mains-powered interlinked smoke alarms with standby power in the circulation space on every storey, plus a heat alarm in the kitchen if it opens onto the stairway or hallway without a door.
Where should smoke alarms be fitted?
On the ceiling in the hallway and on every landing, at least 300mm from walls and light fittings, and within 7.5m of the door to every habitable room. Keep them out of bathrooms and away from directly above the hob.
Do I need a carbon monoxide alarm with a new boiler?
Yes. Since 1 October 2022, Approved Document J has required a carbon monoxide alarm in the room when any fixed combustion appliance is installed or replaced, including boilers and wood burners. Gas cookers are excluded.
What are landlords' smoke alarm rules in England?
At least one smoke alarm on each storey with living accommodation, a carbon monoxide alarm in any room with a fixed combustion appliance other than a gas cooker, and repair or replacement once told an alarm is faulty. Councils can fine up to £5,000.
Sources
- GOV.UK, Approved Document B: fire safety, volume 1, dwellings: gov.uk
- GOV.UK, Approved Document J: combustion appliances and fuel storage systems: gov.uk
- GOV.UK, Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022: guidance for landlords and tenants: gov.uk
- Scottish Government, fire and smoke alarms in Scottish homes: gov.scot
Checked on 3 October 2026.