The UK is phasing out the BS476 fire testing standard, but with full enforcement not coming in until September 2029, many developers still think they have time. The reality is that waiting too long could lead to delays, redesigns or legal issues that are much harder and more expensive to fix further down the line.
The transition officially started on 2 March 2025, when BS 476 began being phased out from Approved Document B. From 2029, only wall systems tested to the EN 13501-1 standard will be accepted. This approach is based on system-level testing, not just individual materials. It includes large-scale tests like BS 8414, which look at how fire spreads across a full façade. Internal elements are assessed using BS EN 1364-1 and BS EN 1365-1, which measure fire resistance and how well fire is contained.
This marks a big change not only in how systems are tested but in who is held responsible when something goes wrong.
What’s Changing and Why It Matters
EN 13501-1 requires wall systems to be tested as complete assemblies. That means insulation, cladding, cavity barriers and fixings all need to be assessed together, rather than separately. Fire doesn’t spread in neat lines, and testing now needs to reflect that.
This is a shift from the BS 476 method, which relied on small-scale tests like Part 6 and Part 7 that looked at individual materials. EN 13501-1 introduces a wider classification system that includes Euroclass ratings such as A1 and A2-s1,d0, and takes into account smoke production and flaming droplets.
Some developers assume that using CE-marked or A2-rated products is enough, but it isn’t. Under the new system, you need test evidence showing how the whole system performs when installed on a building.
Why Whole-System Testing Matters
Even if each material passes testing on its own, that doesn’t mean it will perform the same way in a finished wall. Materials can interact in unexpected ways, which can lead to fire spread, structural failure or excess smoke.
Joe Ragdale, Technical Director at Wetherby Wall Systems says “The minimum legal requirement has shifted, but best practice is going further. Designers and contractors need to think in terms of full system performance, not just the material label.”
BS 8414 tests are often used to understand how a façade reacts in real fire conditions. For internal walls and floors, BS EN 1364-1 and 1365-1 help assess how well fire can be contained. These standards are especially important in high-rise buildings, student accommodation and other multi-occupancy spaces.
The Cost of Falling Behind
As of February 2025, only 46% of high-rise buildings applying to the Building Safety Fund for unsafe non-ACM cladding had completed remediation work. Progress has been slow, even as expectations rise.
Remediation costs have already passed £16 billion, and through the Cladding Safety Scheme, the government is starting to recover those costs from the original developers and contractors.
Accountability Is Also Increasing
The Building Safety Act 2022 brings in stricter responsibilities for those involved in building design and delivery. Principal Designers, Contractors and Accountable Persons can now be held legally responsible for safety issues, including those on past projects. The Act includes a 30-year retrospective liability period and requires a clear digital record of safety-critical decisions, known as the golden thread.
Choosing not to act now doesn’t just create risk for today’s builds. It creates a long-term liability that could resurface years from now.
What Developers Should Be Doing Now
To stay on track and avoid problems further down the line, developers and specifiers should:
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Use wall systems that have been tested as a complete build-up
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Choose materials that meet A2-s1,d0 or better
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Make sure barriers, fixings and insulation are tested as part of the same system
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Work with suppliers who can provide full documentation and technical support
“The cost of non-compliance isn’t just legal, it’s reputational and commercial,” adds Ragdale. “If your design only meets today’s standards, it could fall short in just a few years. Planning ahead protects both the building and your business.”
weAbout Wetherby Wall Systems
Wetherby Wall Systems is a UK supplier of certified external wall insulation (EWI), specialising in A1-rated systems for masonry, steel and timber frame applications. With over 40 years of experience, Wetherby supports developers with specification, testing and installation guidance. Find out more about their A1 Non-Combustible EWI Systems on their website.