Kelly Westwood, Head of Construction Projects at Knauf Insulation, discusses how changes to Part B will affect insulation specification.
Since June 2022, anyone involved in building design and construction has understandably been focused on the implications of the changes to thermal performance. But regulations don’t exist in a bubble. It’s not just energy efficiency standards that are getting stricter, those governing building fire safety are too.
In December 2022, a new wave of changes was made to Approved Document B (Part B), which sets out the minimum standards for fire safety in buildings in England and Wales. The transition period is swift. Projects can only be built to the previous standard providing a building or an initial notice, or full plans were given before December 2022 and work has started before June 2023. After this date, all projects must be built to the new standards, regardless of when planning was approved, so architects and specifiers need to get to grips with the changes fast.
What’s changing?
Regulations were last updated in 2018 when the government banned the use of combustible materials in the external walls of relevant residential buildings over 18m tall.
This ban has now been extended to cover the use of combustible materials in the external walls of all residential buildings between 11m and 18m in height. The only exception is in cavity walls or external walls where a full-scale fire test to BS 8414-1 or BS 8414-2 has been successfully conducted. Such tests are prohibitively expensive for most organisations and the system built must be identical to that tested, meaning there’s no possibility to change the specification later. So, in reality, combustible materials have been effectively banned from being used in external wall systems such as rainscreen façades or timber frames on all residential buildings between 11m and 18m tall.
It’s worth noting that in her report on the Grenfell tragedy, Dame Judith Hackitt stated that large-scale fire tests don’t reflect real-world ‘as-built’ structures. Indeed Scotland, which doesn’t fall under the Part B regulations, has already banned the use of testing to BS 8414-1 and -2 in relation to fire safety for residential buildings.
The definition of relevant residential buildings over 18m has also been updated. When the definition was introduced, it encompassed buildings containing one or more dwellings, rooms for residential purposes (such as student accommodation or hospitals) or an institutional building.
But there were key omissions – rooms for residential purposes did not include hotels for example. Many saw this as an oversight, especially as hotel guests woken from slumber in unfamiliar surroundings may find it harder to escape smoke-filled corridors than those who live in, and therefore navigate, a property day in and day out. As a result, the list of relevant residential buildings has now been extended to include hotels, hostels and boarding houses.
The changes to Part B also affect the materials that can be used in non-dwelling building types. All buildings less than 1000mm from the relevant boundary must use materials with a reaction to fire classification of B,s3 d2 or better, but this does not apply to buildings under 18m tall over 1000mm from the boundary.
While all these changes are designed to improve the safety of building occupants, they introduce a level of complexity that could cause confusion for designers and specifiers. After all, if your project fell under the spotlight, would you be truly confident that you understand the risks involved with using different products for every type and height of building? If the answer is no, and you don’t have access to technical teams to determine the risk of every build, then what should you do?
Choose non-combustible to reduce fire risk
The simplest solution is to specify non-combustible materials as standard, such as glass and rock mineral wool insulation which have the highest Euroclass A1 or A2-s1,d0 reaction to fire classification. All CE marked materials are given a Euroclass reaction to fire classification to determine their combustibility rating. Materials are classified under BS EN 13501-1 where they undergo a series of tests to determine whether they will ignite, produce smoke or flaming droplets. The classifications range from F (easily flammable/the lowest) to A2-s1,d0 and A1 (non-combustible/the highest).
Non-combustible insulation meets the most stringent requirement of the building regulations and can be used in the external walls of relevant residential buildings over 18m tall or residential buildings between 11m and 18m, without the need for a large-scale test.
This contrasts with oil-based rigid board insulation which is combustible. PIR insulation typically achieves between a B and an F Euroclass reaction to fire classification, PUR and Phenolic fall between categories B and E, and EPS and XPS into E or F (easily flammable).
Where fire safety is concerned, there’s no room for grey areas. It is imperative to not only design the fire risk out of buildings, but to also specify and use materials that contribute to the building’s fire safety strategy. The safest and simplest way to do that is to choose non-combustible mineral wool insulation, whatever the height or use of the building.
