Approved Document B: Fire safety

Answers to frequently asked questions on Approved Document B including 2020 and 2022 amendments.

These frequently asked questions (FAQs) refer to the Fire safety: Approved Document B.

For the purposes of Part B of the Building Regulations a Grade D2 Category LD3 system is considered to be adequate. Therefore, as a minimum, the system itself should be designed and installed in accordance with the guidance for a Grade D2 LD3 systems in BS 5839-6:2019.

The Housing Act 2004 replaced the previous housing fitness standard with a statutory framework for assessing and tackling hazards in housing - including fire hazards. Within a house designated as a ‘House in Multiple Occupation’ such devices may still need to be provided between the private areas (i.e., bedrooms) and the common parts (i.e., circulation spaces, living room, kitchen etc). Further guidance on fire safety provision can be found in the Local Authorities Coordinators of Regulatory Services (LACORS) guide titled Guidance on fire safety provisions for certain types of existing housing.

A protected stairway should be enclosed with fire resisting construction and fire doorsets in order to protect people escaping down the stairs from a fire in the accommodation. It may not always be necessary to provide fire doorsets on cupboards if they are small and the fire risk is low. An alternative to providing a fire doorset on a bathroom is to include the bathroom within the stair enclosure, thus removing the need for a fire doorset.

Guidance on loft conversions is provided in Volume 1 of Approved Document B.

A fire doorset should be regarded as a complete installed assembly. Thus, the door, the frame and any ironmongery should be considered when assessing its suitability. In most cases, however, it should be possible to retain the existing frame. If in doubt, the test report for the door being installed will include details of the door frame in which it was tested. Fire doorsets are often thicker and much heavier than other internal doors. Where existing frames are retained, it may be necessary to replace or relocate the door stops and to install additional fixings back to the structure. The joint between the frame and the surrounding structure should be adequately fire stopped and the operating gap between the door and the frame should be kept to a minimum (usually 3-4mm).

Door closers are not required for internal fire doorsets in flats, when they are being used to provide lobby protection for a common stair. However, the recommendation for the provision of fire doorsets remains as does the advice to householders that doors should be kept shut, especially at night.

Paragraph 2.43 in Volume 2 of Approved Document B states; "Bedrooms should not contain more than one single or double bed". This is for a design, without sprinklers, relying upon fire resisting construction to protect occupants that are remote from the seat of fire. Research on sprinkler effectiveness in care homes has shown people who are in intimate contact with a fire, for example where clothing or bed linen is alight, are unlikely to benefit from the operation of sprinklers. However, where sprinklers are provided, people who may be in the same room but not in intimate contact with the fire (for instance in another bed) will have an increased chance of survival. It is not the intention of the Approved Document to separate couples who happen to live in a care home by insisting that they sleep in separate beds.

Diagrams 5.2a (Volume 1) and 8.2a (Volume 2) of Approved Document B apply a more onerous standard than Diagrams 5.2b and 8.2b, any combustible (including thermosetting) core panels should incorporate a band of material rated A2 -s3, d2 or better 300mm wide centred over the wall.

In low-rise residential, office or assembly buildings to which Diagram 5.2b (Volume 1) and 8.2b (Volume 2) applies, panels with thermosetting cores can be used without a 300mm band of material A2 s-3, d2 material. However, fire-stopping must be provided to seal the joint between the compartment wall and the underside of the panel. Any voids above the panel (such as where an additional roof covering is provided) should also be adequately fire-stopped.

Regulation 4 (1) of the Building Regulations 2010 states that "building work" should comply with the applicable requirements contained in Schedule 1. Regulation 4(3) then goes on to state that after the work is completed the building as a whole should comply with the applicable requirements of Schedule 1 or, where the building did not previously comply with any such requirement, is no more unsatisfactory in relation to that requirement than before the work was carried out.

Where an existing shop is extended such that the final floor area is greater than 2000m2 (whether it exceeded this value previously or not) then the building as a whole may be less satisfactory in relation to Schedule 1 requirement B3(3) than before the work was carried out. Therefore, the building would have to be either subdivided to limit the compartment size, fitted with sprinklers or some other solution would be necessary in order to satisfy regulation 4(3) in relation to requirement B3. Regulation 4(3) must be judged against the requirements set out in Schedule 1 rather than the Approved Document. B3(3) requires sub-division of the building "to an extent appropriate" to its size and intended use and it may be that some buildings will still comply with requirement B3(3) by virtue of its intended use even though they have been extended without further compartmentation

This would be a matter for the designer and the relevant building control body to consider. However, any such proposal may result in the need to upgrade the specification of the sprinkler system and the duration of water supplies.

Sprinklers are shown to benefit life safety by reducing the frequency of significant fires and injuries or fatalities associated with fires. Research by the Building Research Establishment (BRE) into the effectiveness of sprinklers estimates a reduction in deaths and injuries at 90% and 61% respectively when sprinklers are provided in purpose built flats1 with confidence of ±3% and ±12%. More recent analysis from Wales2 considering flats estimates a reduction in deaths and injuries at 90% and 62% respectively with confidence of ±4 and ±12%.

Increasing the period of fire resistance of the compartment walls between flats beyond that specified in the Approved Document is unlikely to have any significant impact on the safety of occupants of the building and would have no discernible benefit to persons in the flat where the fire has started.

1 Cost Benefit Analysis of Residential Sprinklers – Final Report March 2012 (BRE prepared for The Chief Fire Officers Association), page 26.

2 Cost Benefit Analysis of Residential Sprinklers – Report of Cost Benefit Analysis March 2013 (BRE prepared for the Welsh Government) page 29.

No, this is a printing error. The word "over" should be retained as for the 2000 edition of Approved Document B, and so paragraph 9.12 in Volume 2 of Approved Document B should read: "If the cavity is over an undivided area that exceeds 40m in any direction, there is no limit to its size if all of the following conditions are met". The principle of paragraph 9.12 is that it relates to a concealed space over a single undivided room (such as an open plan office). Because the room below the space is undivided, the occupants will be able to see a fire develop and react to the changing hazard, thus cavity barriers within the space above are less important than with a cellular layout. The conditions in paragraph 9.12 are intended to reduce the risk of a fire starting/spreading in the undivided void and to prevent fire entering the void from outside the room which is not visible to its occupants.

The 45m criterion is based on the physiological demands on firefighters engaged in search and rescue and on the restrictions that may be imposed by their equipment. When considering hose length, it is important to appreciate that, in practice, hoses have a tendency to ‘snake’ when charged thus limiting their effective length. It is also common practice to trim the ends of hoses where they become damaged. The time and effort it takes to lay out a hose may also be an important factor.

Paragraph 13.1 in volume 1 of Approved Document Part B states there should be vehicle access for a pump appliance to within 45m of all points within dwellinghouses. This is to take account of the actual distance that the firefighters need to carry kit and lay hoses from the vehicle to reach a potential fire.

Provision of water supplies does not, on its own, reduce the physiological impact on firefighters of travelling long distances whilst carrying heavy equipment. Water from private hydrants may still need to be pumped before it can be used for firefighting.

Where it is proposed to adopt an alternative approach to meeting requirement B5 (Access and facilities for the fire service) It would be advisable to seek the advice of the fire and rescue service who can advise on the practicalities of firefighting.

Approved Document B recommends that there should be vehicle access for a pump appliance to within 18m of the dry main connection point, inlets should be on the face of the building. This is to take account of the actual distance that the fire fighters need to carry kit and lay hoses from the vehicle to the building and the time it takes to charge the main.

In some situations where the 18m distance cannot easily be met, it may be acceptable to extend the connection point beyond the face of the building to reduce the distance. However, this will not, on its own, reduce the physiological impact on firefighters of travelling long distances while carrying heavy equipment. Where it is proposed to adopt an alternative approach to meeting requirement B5 (Access and facilities for the fire service) it would be advisable to seek the advice of the fire and rescue service who can advise on the practicalities of firefighting.

Designers should discuss and agree the design intent and the necessary evidence with the building control body before starting building work.

As set out within Approved Document B, the guidance is provided for common building situations. Tall, large, or complex buildings, where the structure is able to contribute as a source of fuel during a fire, are not common building situations and present additional considerations which designers should have regard to.

The designer should consider the type of construction, alongside factors influencing the consequences of fire spread and fire induced structural failure such as height, size, and use of the building, when considering whether it is appropriate to apply the provisions in Approved Document B.

Following the guidance in Approved Document B, including the minimum fire resistance periods and the standard test methods, may not be sufficient to meet the requirements of the building regulations, particularly in cases where the consequences of fire spread, and fire induced structural failure are more significant.

Where alternative methods of complying with the building regulation requirements are adopted, it is likely to require a detailed, evidence-based, understanding of fire performance for the specific design demonstrating how each of the building regulation requirements will be addressed directly.

Note 1: Whatever design method is applied, the functional requirements of the building regulations must be met for all building work. This applies to all those responsible for building work including the building owner, agents, designers, builders and installers.

Note 2: For relevant buildings, Regulation 7(2) and 6(3) control the use of combustible materials in and on external walls.

Designers should discuss and agree the design intent and the necessary evidence with the building control body before starting building work.

As set out in Approved Document B, the guidance is provided for common building situations. Tall, large, or complex buildings, where alternative structural failure mechanisms or unusual routes for internal fire spread might exist, are not common building situations and present additional considerations which designers should have regard to.

The designer should consider the type of construction, alongside factors influencing the consequences of fire spread and fire induced structural failure such as height, size, and use of the building, when considering whether it is appropriate to apply the provisions in Approved Document B.

Following the guidance in Approved Document B, including the minimum fire resistance periods and the standard test methods, may not be sufficient to meet the requirements of the building regulations, particularly in cases where the consequences of fire spread, and fire induced structural failure are more significant.

Where alternative methods of complying with the building regulation requirements are adopted, it is likely to require a detailed, evidence-based understanding of fire performance for the specific design demonstrating how each of the building regulation requirements will be addressed directly.

Note 1: Whatever design method is applied, the functional requirements of the building regulations must be met for all building work. This applies to all those responsible for building work including the building owner, agents, designers, builders and installers.

When an approved document refers to a named standard, the relevant version of the standard is listed at the end of the approved document. Until the approved document is amended, these references are part of the guidance approved under section 6 of the Building Act.

If work complies with the guidance referred to in the approved document, that makes it likely that the work conforms with the relevant requirements of the Building Regulations. Following other guidance would not provide that legal protection.

If an approved document refers to an older version of a standard that the issuing standards body has now revised or updated, the new version may be used as a source of guidance, provided it continues to address the relevant requirements of the Building Regulations.

For details, please see the Manual to the Building Regulations.

Each case must be considered on its own merits, but it is likely that where additional storeys are added to an existing building, some work on the original part of the building will be necessary.

Applicants and building control bodies are reminded of the need to consider these new provisions sprinklers in relation to extensions as required by Regulation 4(1). New accommodation, formed by building work, should meet the relevant requirements having considered the guidance in the approved document. This means ensuring that the standard of fire protection for the occupants of the new accommodation is as would be provided for a newbuilding under the approved document. In the majority of cases, therefore, sprinkler protection will be necessary in any newly formed accommodation that falls above the new 11m trigger height.

It may also be necessary to consider additional protection for the existing parts of the building where needed to ensure that the extension is compliant with the applicable requirements of Schedule 1. Equally, it will be necessary to satisfy regulation 4(3) by ensuring that the level of fire protection in the building as a whole is made no worse.

There may also be situations where the risk assessment for the building (provided under the Fire Safety Order) requires further work to be done. Regardless of the minimum requirements of the regulations there is, of course, merit in providing additional protection throughout the building.

Further advice can be found in the following circular letter.

In many cases premises which are like a family home can be designed in accordance with Volume 1 (Dwellings). However, self-catering holiday homes, and short term lets are subject to the Regulatory Reform (Fire Safety) Order 2005, and it may be necessary to take account of the duties imposed under that Order in the design of the premises.

The Department's leaflet, Do you have paying guests? provides some useful guidance on the application of the Fire Safety Order to B&Bs, guest houses, short term lets and self-catering properties. Regardless of the design guidance that is adopted it will still be necessary for Building Control Bodies to consult with Fire and Rescue Authorities on work relating to buildings where the Fire Safety Order is (or will be) applicable. This should ensure that any potential problems can be identified before building work is started self-catering properties. Regardless of the design guidance that is adopted it will still be necessary for Building Control Bodies to consult with Fire and Rescue Authorities on work relating to buildings where the Fire Safety Order is (or will be) applicable. This should ensure that any potential problems can be identified before building work is started.

Further guidance on the consultation process is given in the Building Regulations and Fire Safety Procedural Guidance published by Local Authority Building Control (LABC), with the National Fire Chiefs Council (NFCC) and the Association of Consultant Approved Inspectors (ACAI) and in conjunction with the Joint Regulators Group.