Smoke and Carbon Monoxide Alarm Regulations When Selling

Smoke alarms and carbon monoxide detectors are one of those areas where the legal requirements for sellers are less clear-cut than most people assume. There is no single law that says “you must have working smoke alarms to sell your house,” but the practical reality is that Building Regulations, buyer expectations, surveyor reports, and mortgage lender requirements all converge to make adequate fire and CO detection an effective necessity for any property sale.

This guide explains the regulations that apply to smoke and carbon monoxide alarms in residential properties for sale in England and Wales. It covers Building Regulations Part B, the landlord-specific 2022 regulations, the different types and grades of alarm, where they should be placed, and what you should do as a seller to ensure your property is compliant and ready for the market.

The regulatory framework: what applies to sellers?

Smoke and carbon monoxide alarm requirements come from two main sources of regulation, and which one applies depends on whether building work has been carried out and whether the property is owner-occupied or tenanted.

Building Regulations Approved Document B (Fire Safety)

Approved Document B is the section of the Building Regulations for England that deals with fire safety. It applies to all properties where notifiable building work has been carried out, regardless of tenure. This includes new builds, extensions, loft conversions, material alterations, and certain changes of use. In Wales, the equivalent requirements are set out in the Welsh Government's version of Part B.

Since 1992, Approved Document B has required smoke detection in new dwellings. The requirements have been strengthened over successive revisions, and the current edition (2019, with 2020 amendments) requires:

• At least one smoke alarm on every storey that contains a habitable room
• A heat alarm in the kitchen (not a smoke alarm, which would cause nuisance false alarms from cooking)
• All alarms to be interlinked, so that activation of one alarm triggers all others
• Alarms to be mains-powered with battery backup (Grade D under BS 5839-6)
• A carbon monoxide alarm in any room containing a fixed combustion appliance (excluding gas cookers), as required by Approved Document J

If your property has had building work that was subject to building regulations approval, the alarm installation should have been inspected and signed off as part of the building control process. If alarms were required but were never installed, or were installed but have since been removed, this represents a building regulations compliance gap that the buyer's solicitor is likely to raise.

Smoke and Carbon Monoxide Alarm Regulations 2015 and 2022

The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, as amended by the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, impose specific duties on landlords of residential properties in England. These regulations do not apply to owner-occupier sellers.

Since 1 October 2022, landlords must:

• Install at least one smoke alarm on every storey of a rented property that contains a habitable room
• Install a carbon monoxide alarm in any room that contains a fixed combustion appliance (excluding gas cookers)
• Ensure all alarms are in proper working order on the day a new tenancy begins
• Repair or replace any alarm reported as faulty by a tenant

The 2022 amendment extended the carbon monoxide alarm requirement to cover all fixed combustion appliances, not just solid fuel appliances as was previously the case. This means that rooms with gas boilers, gas fires, and oil-fired appliances must now have a CO alarm in rented properties.

If you are a landlord selling a tenanted or previously rented property, the buyer's solicitor will expect you to confirm compliance with these regulations. If you are an owner-occupier, these regulations do not legally bind you, but buyer expectations are increasingly shaped by them.

What owner-occupier sellers should provide

As an owner-occupier, your legal obligations around smoke and CO alarms when selling are determined by whether building work has been carried out on the property. However, the practical expectations go further than the minimum legal position. Here is what you should consider:

Properties with building work history

If your property has had any of the following work, Building Regulations Approved Document B will have required smoke and possibly carbon monoxide alarms:

• New build. All new dwellings built since 1992 should have smoke detection meeting the building regulations standard in force at the time of construction.
• Extensions and loft conversions. Building regulations require smoke alarms throughout the property when an extension or loft conversion is carried out, not just in the new space. The requirement is for a Grade D system with interlinked mains-powered alarms.
• Material alterations. Work that alters the structural integrity of the property or affects fire escape routes may trigger a building regulations requirement for upgraded fire detection.
• Change of use. Converting a building or part of a building to residential use triggers full building regulations compliance, including fire detection.

The buyer's solicitor will check building regulations completion certificates for any work carried out on the property. If certificates show that work was done but there are no functioning alarms that match the specified grade, this will be raised as an enquiry. Having the correct alarms in place and operational before you list avoids this issue entirely.

Properties with no building work history

If your property is an older home with no extensions, conversions, or other notifiable building work, there is no building regulations requirement for smoke alarms. You are not legally obliged to install them for the sale.

That said, the absence of any smoke detection in a property will be noted by the buyer's surveyor and is likely to be flagged in their report. Buyers purchasing with a mortgage may find that their lender requires smoke alarms to be installed as a condition of the mortgage offer. Even if the lender does not make it a formal condition, the surveyor's recommendation creates a negotiation point that buyers may use to request a price reduction or to require alarms as a condition of proceeding.

The TA6 and disclosure

The TA6 Property Information Form requires sellers to disclose information about the property's services, safety features, and any building work that has been carried out. You should confirm what fire detection systems are installed, whether they are mains-powered or battery-operated, and whether they were installed as part of building regulations compliance. Providing clear, honest answers on the TA6 reduces the likelihood of additional enquiries and demonstrates transparency. For a full picture of the documents you need, see our guide on documents needed to sell a house.

Types of smoke and heat alarm

Not all smoke alarms work in the same way, and using the right type in the right location matters for both safety and practical compliance. There are three main types of smoke detector used in domestic properties, plus heat alarms for kitchens:

Ionisation smoke alarms

Ionisation alarms contain a small amount of radioactive material (americium-241) that ionises the air between two electrodes. When smoke enters the chamber, it disrupts the ionisation current and triggers the alarm. Ionisation alarms are most responsive to fast-flaming fires — fires that produce small smoke particles, such as burning paper or flaming wood. They are less effective at detecting slow, smouldering fires.

Ionisation alarms are prone to false alarms from cooking fumes, steam, and dust, which makes them unsuitable for kitchens or locations near bathrooms. They are increasingly being replaced by optical alarms in new installations.

Optical (photoelectric) smoke alarms

Optical alarms use a light source and a photosensor inside the detection chamber. In normal conditions, the light beam does not reach the sensor. When smoke enters the chamber, it scatters the light onto the sensor, triggering the alarm. Optical alarms are most responsive to slow, smouldering fires — fires that produce large, visible smoke particles, such as smouldering furniture, overheating wiring, or cigarettes.

Optical alarms are less prone to false alarms from cooking and steam than ionisation models, making them more suitable for hallways, landings, and living areas. They are the preferred type for most domestic installations and are the type most commonly specified under current building regulations guidance.

Heat alarms

Heat alarms do not detect smoke at all. Instead, they trigger when the temperature in the room rises above a set threshold (typically 58°C for a fixed-temperature alarm) or when the rate of temperature rise exceeds a certain level (rate-of-rise alarms). Heat alarms are designed specifically for kitchens and other areas where smoke alarms would cause frequent false alarms. Building Regulations Approved Document B specifically recommends heat alarms in kitchens rather than smoke alarms.

Multi-sensor alarms

Multi-sensor alarms combine optical smoke detection with heat detection in a single unit. By analysing both smoke and temperature readings, they provide broader fire detection coverage while reducing false alarm rates. Multi-sensor alarms are more expensive than single-sensor models but offer the best all-round performance for hallways and living areas.

Interlinked alarm systems

Interlinking means that when one alarm in the system detects smoke or heat, all alarms sound simultaneously. This is critical in multi-storey homes where a fire on one floor might not be heard on another without interlinking.

There are two ways to interlink alarms:

• Hard-wired interlinking. Alarms are connected by cable, typically run during construction or building work. This is the standard approach for new builds and extensions where cables can be routed through walls and ceilings during the build. Hard-wired systems are the most reliable form of interlinking.
• Radio frequency (RF) wireless interlinking. Alarms communicate with each other via radio signals, with no physical cable connection. RF interlinking is ideal for retrofitting older properties where running new cables would be impractical or disruptive. Modern RF-interlinked alarms are highly reliable and meet the requirements of BS 5839-6 for Grade D systems.

Building Regulations Approved Document B requires interlinked alarms for new builds and extensions. If you are retrofitting alarms in an older property to improve saleability, RF wireless interlinked alarms are a cost-effective solution that avoids the need for rewiring. A set of RF-interlinked mains-powered alarms with battery backup typically costs £150 to £300 for a three-bedroom house, installed by a qualified electrician.

BS 5839-6: grades and categories explained

BS 5839-6 is the British Standard that covers the design, installation, commissioning, and maintenance of fire detection and fire alarm systems in domestic premises. Building Regulations Approved Document B references BS 5839-6 when specifying what type of alarm system is required.

The standard defines systems by grade (the type of equipment and power supply) and category (the extent of coverage).

Grades

Categories

The category defines how much of the property the alarm system covers:

• LD1: Alarms in all rooms (except bathrooms and shower rooms). Maximum coverage for life safety.
• LD2: Alarms in escape routes (hallways, landings, staircases) plus rooms that present a high fire risk (kitchens, living rooms with open fires, rooms with electrical equipment). This is the most common category specified by building regulations for new builds.
• LD3: Alarms in escape routes only (hallways, landings, staircases). This is the minimum level specified by building regulations for some extensions and alterations.

For most new builds and extensions, Building Regulations require a Grade D, Category LD2 system as a minimum. This means mains-powered interlinked alarms with battery backup, installed in escape routes and high-risk rooms. Some building control bodies may accept LD3 for minor extensions where fire risk is low, but LD2 is the standard recommendation.

Where alarms should be placed

Correct placement is as important as choosing the right type of alarm. Building Regulations Approved Document B and BS 5839-6 provide detailed guidance on positioning:

Smoke alarms

• At least one on every storey that contains a habitable room
• In hallways, landings, and on the ceiling of the escape route at each level
• On the ceiling, at least 300 mm from any wall or light fitting
• Within 7.5 metres of the door to any habitable room (for LD2 and LD3 coverage)
• Not in kitchens, bathrooms, or shower rooms (use heat alarms in kitchens instead)
• Not directly above heat sources such as radiators or boilers

Heat alarms

• In the kitchen, on the ceiling
• At least 300 mm from any wall and away from the cooker (to avoid nuisance activations from normal cooking)
• Interlinked with the smoke alarms in the rest of the property

Carbon monoxide alarms

• In any room containing a fixed combustion appliance (gas boiler, gas fire, wood-burning stove, oil-fired boiler)
• At head height on a wall, between 1 and 3 metres horizontally from the appliance
• Not directly above the appliance, not near a window or ventilation opening, and not in an enclosed space
• In the room where the appliance is located, not in an adjacent room or hallway

Approved Document J (Combustion Appliances and Fuel Storage Systems) requires a carbon monoxide alarm whenever a new or replacement fixed combustion appliance is installed, regardless of fuel type. If your property has had a boiler replacement, a new wood burner, or any other combustion appliance fitted, a CO alarm should have been part of the installation.

Building control requirements for new builds and extensions

If your property is a new build or has had an extension, loft conversion, or other notifiable building work, the fire detection system should have been inspected and approved by building control as part of the sign-off process.

What building control checks

The building control officer will verify that the alarm system meets the grade and category specified in the approved plans. For a typical new-build house or an extension, this means checking that:

• Mains-powered interlinked smoke alarms with battery backup are fitted on every storey (Grade D)
• A heat alarm is fitted in the kitchen, interlinked with the smoke alarms
• Carbon monoxide alarms are fitted in rooms with fixed combustion appliances
• Alarms are correctly positioned according to BS 5839-6
• The interlinking is functional (activating one alarm triggers all others)

If the alarm system was not properly installed or has been modified since sign-off, this may be flagged as a building regulations compliance issue during the sale. The buyer's solicitor will check the building regulations completion certificate and may query whether the alarm system is still in the condition it was when building control signed it off.

Missing building control sign-off

If building work was carried out without building regulations approval, or if approval was obtained but the work was never signed off with a completion certificate, the absence of compliant smoke alarms may be part of a broader compliance gap. In this situation, you have several options:

• Regularisation. You can apply to your local authority building control department (or an approved inspector) for retrospective approval of the work. This involves an inspection of the work as it stands and a fee, and the building control officer will check whether the fire detection meets the standard that applied at the time of the work.
• Install compliant alarms. If the only issue is missing or inadequate alarms, installing the correct system may be sufficient to satisfy the buyer's solicitor without a full regularisation application. This is the quickest and cheapest solution if the rest of the building work is satisfactory.
• Indemnity insurance. If regularisation is not practical (for example, if the work was done many years ago and accessing concealed elements for inspection would be disproportionately disruptive), indemnity insurance can be obtained to protect the buyer and their lender against the risk of enforcement action. See our guide on building regulations sign-off missing for more detail on this option.

What buyers expect

Buyer expectations around smoke and CO alarms have increased significantly in recent years, driven by the landlord regulations, higher public awareness of fire safety, and more thorough surveyor reporting. Here is what most buyers and their advisors will look for:

• Working smoke alarms on every floor. This is the baseline expectation. A property with no smoke alarms at all will raise concerns and is likely to generate enquiries.
• A heat alarm in the kitchen. Buyers familiar with current building regulations or who have recently purchased a new build will expect a heat alarm in the kitchen rather than a smoke alarm.
• Carbon monoxide alarms near gas and solid fuel appliances. With increased awareness of CO poisoning risks, buyers expect CO alarms in rooms with boilers, gas fires, and wood burners. Providing a gas safety certificate alongside CO alarms gives the strongest reassurance.
• Interlinked alarms in properties with building work. If the property has had an extension or conversion, the buyer will expect the alarm system to match the building regulations standard that applied when the work was done.
• Evidence of building regulations compliance. Completion certificates, electrical installation certificates (for mains-powered alarms), and any documentation showing that alarms were inspected and approved by building control. For more on electrical certificates when selling, see our dedicated guide.

Landlord obligations when selling a rental property

If you are a landlord selling a property that is currently tenanted or has been rented out, the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 impose specific requirements that go beyond the building regulations baseline.

As of 1 October 2022, you must have:

• At least one smoke alarm on every storey of the property that has a habitable room
• A carbon monoxide alarm in every room with a fixed combustion appliance (excluding gas cookers)
• All alarms in proper working order at the start of each new tenancy

Non-compliance can result in a remedial notice from the local housing authority, and failure to comply with a remedial notice can lead to a civil penalty of up to £5,000. The buyer's solicitor will check that the property meets these requirements and may ask for evidence of compliance, particularly if the property is being sold as an investment with a tenant in situ.

Note that the 2022 regulations do not require landlords to install interlinked or mains-powered alarms. Battery-powered standalone alarms are sufficient to meet the landlord regulations, although interlinked mains-powered alarms exceed the requirement and are preferable. The regulations also do not mandate a specific grade under BS 5839-6 — that requirement comes from Building Regulations Approved Document B where building work has been done.

Practical steps for sellers

Regardless of your legal obligations, taking the following steps before you list your property will prevent alarm-related issues from slowing down your sale:

1. Walk through the property and check every alarm. Press the test button on each smoke, heat, and CO alarm. Replace any that do not sound, have expired batteries, or are past their recommended replacement date (typically 10 years for smoke and heat alarms, 5 to 7 years for CO alarms).
2. Check building regulations records. If the property has had building work, check the completion certificate to confirm what alarm system was required. Verify that the installed system still matches. If alarms have been removed or replaced with non-compliant units, bring the system back to the required standard.
3. Install smoke alarms on every floor. Even if not legally required, fitting at least one optical smoke alarm on every storey is an inexpensive step that prevents buyer enquiries and surveyor recommendations.
4. Fit a heat alarm in the kitchen. This shows awareness of current best practice and is expected in any property with recent building work.
5. Install CO alarms near combustion appliances. Place a carbon monoxide alarm in every room that has a gas boiler, gas fire, wood burner, or oil-fired appliance. This complements a gas safety certificate and demonstrates a thorough approach to safety.
6. Consider upgrading to interlinked alarms. If your property has standalone battery alarms, upgrading to RF wireless interlinked alarms is a relatively low-cost improvement that adds genuine safety value and meets the highest buyer expectations. A qualified electrician can install a full system in half a day.
7. Document what you have. Note the make, model, and installation date of each alarm, and whether they are interlinked. Include this information in your responses on theTA6 form. The more detail you provide upfront, the fewer follow-up enquiries the buyer's solicitor will raise.

Cost of compliance

Compared with many aspects of sale preparation, bringing your smoke and CO alarms up to a good standard is inexpensive:

For most properties, a set of interlinked alarms covering all floors plus a kitchen heat alarm and one or two CO alarms will cost under £200 for the units themselves, plus electrician fees if you want mains-powered installation. This is a small outlay compared with the potential delay and cost of dealing with buyer enquiries, surveyor recommendations, or building regulations queries during the sale.

Sources

• Building Regulations Approved Document B (Fire Safety), Volume 1: Dwellings, 2019 edition with 2020 amendments — GOV.UK
• Building Regulations Approved Document J (Combustion Appliances and Fuel Storage Systems) — GOV.UK
• Smoke and Carbon Monoxide Alarm (England) Regulations 2015 — legislation.gov.uk
• Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 — legislation.gov.uk
• BS 5839-6:2019 — 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 — BSI
• National Fire Chiefs Council — Smoke and carbon monoxide alarm guidance
• Law Society — Property Information Form (TA6), 4th edition

Related guides

• Carbon Monoxide Alarm Regulations When Selling

Frequently asked questions