Walls that work under pressure: Why EN 13501-1 changes everything

Joe Ragdale, Technical Director at Wetherby Wall Systems, explores how EN 13501-1 redefines external wall testing and what developers need to do now

BS 476, the UK’s long-standing fire testing standard, is being phased out, and by September 2029, it will no longer be recognised under building regulations.

On the surface, that might feel like a distant deadline, but the reality is that the transition has already begun.

Waiting too long to adapt can result in costly redesigns, project delays, or compliance issues that are far more challenging and expensive to resolve once construction is underway.

The transition to EN 13501-1 has already started

The switch to EN standards isn’t something that’s coming.

It’s already happening.

Since March 2025, BS 476 has started being gradually removed from Approved Document B, signalling a clear move towards EN 13501-1 as the new fire classification benchmark for external wall systems.

By 2029, EN 13501-1 will be the only accepted standard.

That means all external wall build-ups, including cladding, insulation, cavity barriers and fixings, will need to be tested and classified as a full system.

This is a major shift away from the old approach, where materials were tested separately using small-scale tests like BS 476 Parts 6 and 7.

This change is part of a broader effort to strengthen building safety regulations in response to fire safety concerns and ongoing remediation issues.

Since the Grenfell tragedy in 2017, regulatory bodies, industry professionals and government departments have been working to create a more robust, accountable framework that addresses the risks caused by complex wall systems, not just their individual components.

While BS 476 focused on how individual materials behaved in test conditions, EN 13501-1 looks at how everything performs together in a real fire.

What makes EN 13501-1 different?

EN 13501-1 focuses on how the full wall system performs, rather than just the individual materials.

It introduces Euroclass ratings such as A1 or A2-s1,d0, which take into account things like how easily something burns, how much smoke it gives off, and whether it produces flaming droplets.

All of these can make a big difference to how a fire spreads and how safe the building is for people inside.

But ticking off those ratings isn’t enough.

What really matters is how the full wall performs when everything is installed together.

That includes the insulation, cavity barriers, fixings, sheathing boards and final finish.

If one part of that system hasn’t been tested in combination with the others, it may not meet the requirements.

In other words, using A2-rated insulation on its own isn’t enough.

If that insulation hasn’t been tested as part of a complete wall system, it won’t be considered compliant under EN 13501-1.

Why system-level testing matters

Fire doesn’t move in straight lines or follow neat paths.

It spreads in unpredictable ways, and the way materials interact can make a big difference to how a fire develops.

That’s why testing materials separately only tells part of the story.

Just because every product in a wall passes testing on its own, that doesn’t mean the finished wall will perform safely.

A cladding panel and insulation board might both be A2-rated, but without being tested together, with the right barriers and fixings, there’s no way to guarantee they’ll be safe when installed on a building.

That’s where EN 13501-1 comes in.

It requires large-scale testing, typically using BS 8414, to see how fire behaves across a full wall system.

For internal walls and floors, tests like BS EN 1364-1 and 1365-1 are used to assess how well fire is contained within the building.

Joe Ragdale, Technical Director at Wetherby Wall Systems, works with developers across the UK to design fire-safe façades.

He says: “We’re seeing a major shift. It’s not enough to know your materials are rated A2.

“You need to show how the whole system behaves when it’s built.

“That’s the level of detail the new rules demand.”

System-level testing also gives designers and contractors a clearer picture of risk.

Something as simple as the wrong cavity barrier or an off-spec fixing can create a weak point that allows fire to spread.

These are the kinds of issues that wouldn’t show up in small-scale tests.

It also helps to spot inconsistencies in installation that could compromise safety, which is why choosing well-supported systems with full technical guidance is key.

The cost of falling behind

Even though the new standards are already in motion, many buildings are still behind.

As of early 2025, only 46% of high-rise buildings that applied to the Building Safety Fund for non-ACM cladding work had completed the job.

That’s despite the fact that the industry has known this change was coming for a while.

Some developers are still working off outdated assumptions, relying on material-only assessments and thinking they’ll still be allowed a few years from now.

But once BS 476 is fully removed, these systems will no longer be recognised.

That could lead to massive costs.

The total bill for cladding remediation has already passed £16 billion, and government schemes like the Cladding Safety Scheme are now pushing more of the financial responsibility onto the original developers and contractors.

If your design isn’t compliant now, you could end up having to pay for it later.

It’s also worth noting that delays due to non-compliance can hold up planning approval, stop a project mid-build, or trigger retrospective rebuilds, all of which come with a serious price tag.

And if your product or system choice later turns out to fall short, you may not be able to rely on previous approvals as a defence.

Accountability is rising too

On top of the technical changes, the legal framework is tightening as well.

The Building Safety Act 2022 introduced new rules that make Principal Designers, Contractors and other key parties more accountable for safety decisions.

One of the biggest changes is the 30-year retrospective liability period.

That means if something goes wrong years down the line, those involved in the original design and construction could still be held responsible.

There’s also the new requirement for a digital record of safety decisions, known as the “golden thread”.

This includes everything from fire testing data and installation notes to product specifications and maintenance guidance.

Without it, proving compliance will be a lot harder if questions arise in the future.

What developers should be doing now

If you haven’t started preparing for EN 13501-1 yet, now is the time to get moving.

Leaving it until the last minute could result in delays, cost increases and limited access to testing facilities and qualified help.

Start by making sure the external wall systems you specify have been tested as full assemblies.

Look for systems that already meet A1 or A2-s1,d0 ratings, with test evidence covering the insulation, cavity barriers, cladding, fixings and other components all working together.

Make sure you’re working with manufacturers and suppliers who can provide full documentation, including test reports, classification certificates and detailed installation guidance.

This is what will protect your project and your reputation if it’s ever called into question.

As Ragdale says: “This isn’t just a box-ticking exercise.

“It’s about building something that stands up to scrutiny, now and in the future.

“Getting it right today protects your project, your reputation and your business.”

It’s also worth reviewing your internal processes.

Are your design teams fully up to speed with the latest test standards? Is there a clear process for documenting system selection, supplier evidence, and on-site installation details?

Building these habits now will help future-proof your work.

This was originally published in the August 2025 Edition of International Fire & Safety Journal. To read your FREE copy, click here.