Approved Document (Part) B: Fire Safety Building Regulations
What is Approved Document B?
Also referred to simply as ‘Part B’, Approved Document B is one of the essential references when designing under the UK Building Regulations, created to provide guidance on fire safety in the design, construction, and use of buildings.
Published by the UK Government’s Department for Levelling Up, Housing and Communities, it gives guidance to architects, builders, and developers on minimum standards to achieve statutory compliance.
In the document’s introduction it explicitly states, “following the guidance does not guarantee compliance”, so understanding when the guidance is appropriate is key to for anyone proposing to use it. Broadly speaking the guidance in Approved Document B is most appropriate for low rise, non-complex, traditionally constructed buildings.
Approved Document B is split into two volumes:
Volume 1: Focusing on residential buildings, including apartment blocks.
Volume 2: Pertains to all other building types.
Key Objectives of Approved Document B
Approved Document B is structured to achieve five fundamental objectives:
1. Life Safety
The document focuses on protecting building occupants with safe evacuation routes, efficient escape provisions, and appropriate fire alarms.
2. Limit fire spread over internal surfaces
In the event of a fire within the building, the guidance looks to restrict the spread of fire over walls and ceilings in key areas of the building, such as common spaces and larger rooms.
3. Minimising Fire Growth and its impact
Through compartmentation, cavity barriers, fire stopping, and in some cases suppression, the guidance looks to restrict the maximum growth of a fire within a building. Additionally, passive fire resistance is needed to the primary structure to ensure buildings do not prematurely collapse in the event of a fire.
4. Restricting fire spread externally
Guidance is given on external wall and roof construction to limit the spread of fire over the external surfaces of a building. For external walls limitations are also advised to prevent a fire jumping from one building to another.
5. Fire and Rescue Service Requirements
The guidelines give minimum standards for firefighting access and facilities, including reasonable approach and access to the building, firefighting shafts and water provisions.
The Critical Importance of Fire Safety in Building Design
254 fire-related fatalities occurred in England during 2024, as confirmed by official Home Office fire statistics, highlighting the ongoing urgency of fire safety in building design. The devastating Grenfell Tower fire in 2017, which claimed 72 lives, serves as a stark reminder of what happens when fire safety measures fail. These tragedies underscore why Approved Document B remains one of the most critical components of UK building regulations.
Duty Holder Responsibilities
Approved Document B outlines fire safety roles and responsibilities for building owners.
While it doesn’t list enforcement measures or define each duty holder role in detail, it reinforces the link between good design and construction practice enabling the building owner to fulfil their duties in occupation.
Role and Obligations of Duty Holders
Under the Building Safety Act the over arching objective is that duty holders are competent to plan, manage and monitor the delivery of compliant designs and buildings. The Principal Designer should make records of how they fulfil this duty, part of which is to record why the guidance they have used to comply with particular elements of the Building Regulations is appropriate. This is why it is critical for Duty Holders to understand the applicability of any guidance they choose to use.
Approved Document B Volumes
The document is structured into two volumes:
Volume 1: addresses residential buildings, including houses, flats, and residential institutions.
Approved Document B Volume 1 outlines the fire safety requirements for residential ‘dwellings’, ensuring that homes are designed and constructed with consideration for occupant safety.
It covers a wide range of topics, including means of warning and escape, internal fire spread, external fire spread, and access for fire services. On non complex buildings the guidelines provided in this document are the prime reference for architects, builders, and property developers to ensure they at least meet the minimum fire safety standards set by the government.
By adhering to the guidance, on appropriate traditionally constructed buildings, it can significantly reduce the risk of fire-related incidents and protect lives and property. When planning a new traditionally constructed project or renovating an existing home, the design team should familiarise themselves with Approved Document B – Volume 1. It is the first step of the design meeting the functional requirements.
Volume 2: covers all other building types, from commercial offices to industrial facilities.
Approved Document B Volume 2 specifically addresses fire safety in buildings other than dwellings. This document gives guidelines on how to provide minimum levels of fire safety for occupants in commercial, industrial, and public buildings.
The guidance covers the five fundamental areas of fire precautions outlined above, but once again the designer should satisfy themselves that it is appropriate to the size, nature and construction of the proposed building.
By adhering to the guidelines set in Approved Document B Volume 2, professionals in the construction industry can create safer environments, reducing the risk of fire-related incidents, and ultimately protect lives.
Key areas of guidance in Approved Doc B
At its core, Approved Document B gives guidance on meeting five functional requirements laid down in Building Regulations B1 to B5:
B1 – Means of escape looks to enable occupants to safely evacuate during emergencies
B2 – Internal fire spread (linings) looks to limit how fire spreads through interior surfaces
B3 – Internal fire spread (structure) looks to limit the impact and growth of a fire internally, through reasonable structural fire resistance and internal compartmentation.
B4 – External fire spread looks to limit fire transmission between buildings and over the external walls and roofs of buildings.
B5 – Access and facilities for the fire service requires adequate levels of firefighting access and facilities for buildings.
These requirements work together and when complied with will result in a fire safety strategy that looks to protect building occupants while enabling effective emergency response. Understanding and implementing these provisions correctly is essential for creating buildings that have the minimum standards to meet the functional requirements laid down in Regulations B1 to B5 and, more importantly, safeguard human life.
Under the Building Safety Act all duty holders must take all reasonable steps to ensure the design and/or the construction comply with the Building Regulations. For simple, low rise traditionally constructed buildings, Approved Document B is the most common document referred to for guidance on how the design can be developed to comply in terms of fire safety.
Parts B1 – B5 in summary
B1 – Means of Warning and Escape
This requirement focuses on enabling safe evacuation during fire emergencies, such as:
- Travel distances: Maximum distances from any point to nearest exit
- Exit widths: Adequate capacity based on occupancy numbers
- Protected routes: Fire-resistant corridors and stairwells
- Emergency lighting: Illuminated escape routes during power failure
- Fire detection systems: Early warning systems appropriate to building use
B2 – Internal Fire Spread (Linings)
Limits surface materials that could accelerate fire spread within buildings.
- Wall and ceiling classifications: Systems classified to BS EN 13501
- Floor coverings: Guidance is limited to floor surfaces in critical common areas within buildings
- Thermoplastic materials: Restrictions on roof lights and lighting diffusers
- High-risk areas: Enhanced requirements for circulation spaces
B3 – Internal Fire Spread (Structure)
Ensures structural elements provide adequate fire resistance and compartmentation.
- Fire resistance periods: Minimum periods for structural elements
- Compartment walls and floors: Fire-rated separations between spaces
- Openings protection: Fire doors, dampers, fire stopping and cavity barriers
B4 – External Fire Spread
Controls fire spread over external walls, roofs and between buildings, protecting neighbouring properties.
- Boundary distances: Minimum separations from site boundaries dependant on the fire resistance of the wall and the size and number of openings in a particular elevation
- External wall construction: Fire resistance and combustibility requirements
- Roof coverings: Designations under BS EN 13501 based on exposure risk from a fire in adjacent buildings.
B5 – Access and Facilities for the Fire Service
Provides emergency services with the necessary access and firefighting capabilities.
- Vehicle access: Hard-standing areas and access/egress routes
- Fire mains: Wet or dry rising mains depending on the height of the building
- Firefighting shafts: Protected routes for firefighter access, once again, dependent on the height of the building
- Venting systems: Smoke control to protect firefighting shafts and smoke ventilation for basement fires
Amendments to Approved Document B
The UK government has announced a series of updates to Approved Document B (Fire Safety) that will be implemented over the next few years.
2025 amendments
- Transitional Provision
- Initial Notice served prior to 2 March 2025 and started before 2 September 2025
Changes Include:
- Additional requirements for Regulation 38, guidance on fire safety information.
- Removal of national classes for reaction to fire and roofs.
- Introduction of new provisions for sprinklers in all proposed care homes irrespective of height or number of storeys.
2026 Amendments
- Transitional provision
- Initial Notice served prior to 30 September 2026 and started before 30 April 2028
Changes include:
- A new recommendation for more than one common stair to be provided in blocks of flats with a storey 18m or more in height.
- Building design provisions to support the use of evacuation lifts in blocks of flats.
2029 changes
- Transitional provision
- Initial Notice served prior to 30 September 2029 and started before 30 April 2030
Changes focus on the fire safety provisions regarding the removal of national classes for fire resistance:
These phased updates are a result of some of the shortfalls found in the previous guidance following investigations into the Grenfell fire. Building professionals, property owners, and developers should stay informed about these upcoming changes to ensure compliance.
The 2026 changes have been rendered largely irrelevant by the introduction of the control of High Risk (residential) Buildings by the Building Safety Regulator. They have already stated they would not accept a single stair HRB over 18m even though the change in the guidance to Approved Document B has not occurred.
In essence, their expectation is any new build HRB will be designed to BS 9991;2024, which is more onerous than the guidance in Approved Document B. The 2029 amendment lead in is to allow manufacturers with products only tested to the old BS 476 standards, to get them retested under the BS EN 13501 suite.
Practical Implications of Approved Document B
For proposed building works the key thing is for the principal Designer to consider if Approved Document B is the appropriate guidance to use and document their conclusions.
For existing buildings, the building owner has a duty to have adequate fire safety plans in place. To develop these plans, reference should be made to the building design fire strategy. It is surprising how often these documents cannot be provided. In these cases, before any design for an alteration/extension of an existing building takes place, a retrospective fire strategy will have to be authored by a competent professional.
