Design guidance
Approved Document B is the statutory guidance under the Building Regulations 2010 covering fire safety in building design. AD B Volume 1 covers dwellings; AD B Volume 2 covers buildings other than dwellings. This page explains the structure, the post-Grenfell amendments, and what an FRA assessor needs to know.
Two volumes
AD B is published in two volumes. Volume 1 covers dwellings: houses, bungalows, individual flats. Volume 2 covers buildings other than dwellings, including the common parts of blocks of flats, offices, shops, schools, hospitals, hotels and so on.
The two volumes share the same five-Requirement structure but the technical detail differs to reflect the different occupancy patterns, escape strategies, and risk profiles. The 2022 edition was the first to publish the two volumes as substantively different documents rather than one document with annexes; this followed the post-Grenfell push to make the housing-specific guidance clearer in its own right.
For housing fire risk assessors, both volumes matter. The internal of an individual flat is designed to AD B Volume 1. The common parts of the block, the means of escape, the compartmentation between flats and common parts, and the building services in the common parts are designed to AD B Volume 2.
Five Requirements
Post-Grenfell
Following the Grenfell Tower fire in June 2017, the use of combustible materials in the external walls of relevant residential buildings was banned through Regulation 7(2) of the Building Regulations, which came into force in December 2018 and was extended in 2022. The ban applies to buildings with a top storey at least 11 metres above ground level (originally 18m, lowered in 2022) that contain a dwelling, an institution, or a room for residential purposes. Materials in the external wall, attachments such as balconies, and certain specified items must achieve a Euroclass A2-s1, d0 or A1 reaction-to-fire classification.
There are limited exemptions for specific components such as window frames, gaskets, fixings and certain insulation materials in cavity barriers, where the technical requirements of the building cannot reasonably be met using A1 or A2 materials. AD B Volume 2 incorporates the ban and its exemptions in its guidance on Requirement B4.
For an FRA on an existing residential building, the ban is the reference point for assessing whether the external wall system meets current expectations. Buildings constructed before December 2018 (or before December 2022 for the 11-18m extension) may not. The FRA does not by itself require external wall remediation, but it should record the position so the dutyholder can take advice.
BS 9991
For residential buildings, BS 9991 is an alternative to AD B as a route to demonstrating compliance with Requirements B1 to B5 of the Building Regulations. BS 9991 is a fire safety design code specifically for residential buildings, including blocks of flats, sheltered housing and student accommodation. Many post-2017 high-rise residential designs have been carried out to BS 9991 rather than AD B, on the basis that BS 9991 provides a more cohesive treatment of residential-specific risks.
Whether a building was designed to AD B Volume 2 or to BS 9991 affects what the assessor sees on site and what reference document they should bring to the FRA. The fire strategy report for the building, where one exists, will say which standard the design was carried out to. Where the fire strategy report does not exist or cannot be found, the as-built features may need to be inferred from what is present.
For the FRA assessor
A competent housing FRA assessor uses AD B knowledge in several places throughout the assessment. The means of escape evaluation against B1 informs the judgement on whether the escape strategy is still adequate given current occupancy and any building changes since construction. The internal linings inspection against B2 informs whether the surfaces in the common parts still meet the standard the building was designed to. The compartmentation inspection against B3 is one of the most important parts of a competent block of flats FRA. The external wall observation against B4 is the main place the assessor flags any concern that warrants a separate external wall investigation. The fire service access against B5 informs the section on facilities for the fire and rescue service.
None of this means the FRA is checking compliance with the Building Regulations. The FRA is checking whether the existing building presents a tolerable level of fire risk in its current state, given how it was designed and how it is being managed. AD B is the design reference that helps the assessor understand what they are looking at.
Common pitfalls
Software
FRA Flow keeps the design reference material against each property. The building type, fire strategy reference, design standard (AD B or BS 9991), key compartmentation features, escape strategy and any building safety case context are first-class fields on the property record. They appear in the pre-flight pack the assessor sees before going on site, and they sit alongside the on-site observations in the workbench. The competent reviewer can see what design baseline the assessor was working against. The output report carries the same context into the building description section.
This makes the AD B knowledge gap operationally narrower. The assessor still needs to understand AD B to do competent work. The software ensures the design context they need is in front of them when they need it.
FAQ
No. AD B is statutory guidance under the Building Regulations 2010. The Regulations are the law; AD B is one accepted way to comply with Part B of Schedule 1. A building can comply with the Regulations through an alternative route (such as BS 9991 for residential) provided it can be demonstrated to provide an equivalent or better outcome.
Volume 1 covers dwellings (houses and individual flats). Volume 2 covers buildings other than dwellings, including the common parts of blocks of flats. For housing FRAs, both matter: the inside of a flat is designed to Vol 1, the common parts of the block are designed to Vol 2.
No. The FRA is not a Building Regulations compliance check. The FRA assesses fire risk in the existing building given how it was designed and how it is currently managed. AD B is one design reference that helps the assessor understand what they are looking at.
Several amendments. The most prominent was the 2018 ban on combustible materials in external walls of relevant residential buildings (originally 18m+, extended to 11m+ in 2022). AD B was rewritten to incorporate the ban. The 2022 edition also separated AD B Volume 1 and Volume 2 as substantively distinct documents.
Yes, in the sense that the design reference is different. The assessor should know which design route was taken so they can interpret what they see on site against the correct baseline. A BS 9991-designed building may have features that look like divergences from AD B but are intentional design choices under the alternative standard.
Book a 30-minute walkthrough and see how the pre-flight pack and on-site capture keep AD B / BS 9991 context in front of the assessor when they need it.
