Approved Document B is the technical guidance that underpins fire safety in building design across England and Wales. The March 2024 amendments introduce meaningful changes to means of escape, fire detection standards, and compartmentation. If you are building, converting, or significantly refurbishing a property, this affects your project.
Approved Document B (ADB) has been the go-to reference for architects, builders, and fire engineers since the Building Regulations first carved out fire safety into its own approved document. It is split into two volumes. Volume 1 covers dwellings: houses, flats, maisonettes. Volume 2 covers everything else: offices, shops, factories, assembly buildings. Between them, they set out the government’s expectations for how buildings should be designed and constructed to resist fire, protect occupants, and give the fire service reasonable access.
The March 2024 amendments do not rewrite ADB from scratch. They target specific areas where the existing guidance had become outdated or where post-Grenfell reviews identified gaps. That said, the changes are not cosmetic. Several of them will directly affect how buildings are designed and what fire protection systems need to be installed.
What Does Approved Document B Actually Cover?
Before diving into the amendments, it helps to understand the five core areas that ADB addresses. Every fire safety decision in a new build or major refurbishment ties back to one of these.
The five areas are: B1, means of warning and escape. B2, internal fire spread across linings. B3, internal fire spread through structure, which is essentially compartmentation. B4, external fire spread. And B5, access and facilities for the fire service. Each amendment in the March 2024 update touches at least one of these requirement areas.
Key Amendment Areas: What Has Changed
The updated guidance tightens requirements around escape routes in buildings above 11 metres. There is greater emphasis on the provision of a second staircase in taller residential buildings. Travel distances have been reviewed, and the guidance now gives clearer direction on phased evacuation versus simultaneous evacuation strategies. For buildings with a single staircase, the thresholds for requiring additional measures such as sprinkler systems and smoke ventilation have been lowered.
The second staircase question has been a contentious topic in the industry for several years. The government’s position has shifted noticeably since Grenfell: the direction of travel is towards requiring two stairs in residential buildings above 18 metres, with a potential future lowering of that threshold to 11 metres. The March 2024 amendments signal that trajectory clearly, even if they stop short of mandating it for all tall buildings immediately.
Updated recommendations on fire detection grades and categories in residential properties. The amendments align more closely with BS 5839-6:2019 and place stronger emphasis on Grade D1 systems with interconnected smoke and heat alarms in new-build dwellings. Common areas in flats now have more detailed guidance on detection placement and system integration with evacuation alert systems.
Compartmentation is the principle of dividing a building into fire-resisting sections to contain a fire at its point of origin. The amendments clarify requirements for fire-stopping around service penetrations, particularly in walls and floors forming compartment boundaries. Cavity barriers in external wall systems receive tighter specification, reflecting lessons learned from facade fires.
If you have been involved in any refurbishment work on a building with rainscreen cladding, you will know that cavity barriers are where a lot of the practical difficulty lies. The updated guidance does not invent new rules here, but it sharpens the existing ones. The expectation is that designers and contractors demonstrate compliance more clearly at the design stage rather than relying on post-installation inspection to catch deficiencies.
Further restrictions on combustible materials in external wall systems, building on the ban introduced in 2018 for buildings over 18 metres. The amendments extend some requirements to buildings between 11 and 18 metres. Testing and classification standards for external cladding systems are referenced more explicitly, with clearer links to BR 135 and BS 8414 test methods.
The amended Approved Document B applies to all building work where a building notice, initial notice, or full plans application is submitted on or after the amendment effective date. Projects already in progress under prior submissions may continue using the previous edition, but any substantial design changes could trigger a requirement to meet the updated guidance. Check with your Building Control body.
What This Means for Building Owners and Developers
The practical impact depends on what you are doing with your building. For new-build residential developers, the detection and escape route changes are the most immediately significant. Designs that were compliant under the previous edition may need revisiting. Speak with your fire engineer early rather than discovering issues at Building Control submission stage.
For landlords and freeholders of existing buildings, the amendments do not retrospectively apply to your property. But they do signal the direction of regulatory thinking. If you are planning a material change of use, a conversion, or a significant refurbishment, the new edition of ADB will govern your project. That might mean upgrading alarm systems, improving compartmentation, or installing sprinklers that were not previously required.
The Fire Industry Association (FIA) has published useful summaries of how the amendments affect fire detection and alarm installers. If you are an installer or contractor working on fire systems, the FIA’s technical bulletins are worth reading alongside the amended document itself.
We review designs and carry out fire risk assessments with the latest edition of ADB in mind. If you have a project in Cumbria or the North West that is at design stage or about to go through Building Control, we can advise on what the amendments mean for your specific building. Better to sort it out at the drawing board than on site.