Why There's An 18-Metre Rule For Higher Risk Buildings

‍Higher-Risk Buildings Explained: Beyond the 18-Metre Rule

(What London developers and architects really need to understand about the new safety regime)

For a long time, “building height” was the easy way to define risk. If it was tall, it was risky. Simple.But the Building Safety Act 2022 changed that idea completely.

Today, the question isn’t just “How tall is it?”It’s “Who’s inside it, how complex is it, and what happens if something goes wrong?”

At Payte Architects London, we’ve spent the past few years helping clients navigate the shift — from straightforward residential schemes to complex, mixed-use developments across West London: Paddington, White City, Chelsea, and Hammersmith.

And what we’ve seen, again and again, is confusion.Developers and even smaller architectural practices still talk about the “18-metre rule” as though that’s all that matters. But the truth is — height is only one piece of the puzzle.

Let’s unpack what a Higher-Risk Building (HRB) really is, and why this new definition exists.

The 18-Metre Rule — and What It Actually Means

Under the Building Safety Act (BSA) and the Building (Higher-Risk Buildings) Regulations 2023, a Higher Risk Building is defined not just by its height, but by its use and occupancy.

Yes — the benchmark for height is still roughly 18 metres or seven storeys, whichever is reached first.But that alone doesn’t make a building “higher risk.”

The key criteria are:

• It’s at least 18 metres tall or seven storeys, and
  
  
• It contains two or more residential units, or is used as a hospital or care home.
  
  

That second part — the use — is what truly defines the risk.

Why? Because risk in a building isn’t just about how far you have to climb to get out.It’s about who’s inside, how they move, and how complex the structure and systems are in an emergency.

Why the Rule Exists — The Real Reason Behind It

The Grenfell tragedy changed everything.It exposed a industry where design accountability was fragmented — where no single person or company truly owned responsibility for safety throughout the process.

The 18-metre threshold was introduced to identify the buildings that pose the greatest potential risk to life, based on height, complexity, and occupancy.But the Building Safety Act took it further — shifting focus from reactive inspection to proactive accountability.

As Simon Baker, CEO and Founder of Payte Architects London, puts it:

“The old system assumed competence. The new one demands proof. That’s the difference. It’s not just about height anymore — it’s about demonstrating control, clarity, and safety at every stage.”

The rule applies because once a building reaches that scale, the systems — structure, fire, access, evacuation — all become intertwined.A mistake in one can affect everything else.

That’s why the Building Safety Regulator (BSR) now oversees these projects directly, rather than local authorities.It’s a shift from a box-ticking exercise to a duty-led system — where architects, designers, and contractors must actively show how they’re managing risk.

Height Is Only the Start — Other Risk Factors Matter Too

At Payte Architects London, we’ve worked on several projects that technically weren’t tall, but were still classed as higher-risk under the new framework.

Why? Because:

• They involved complex fire strategies (like shared cores or mixed residential and commercial uses).
  
  
• They had vulnerable occupants, such as care homes or assisted-living schemes.
  
  
• They were densely populated developments, where safe evacuation and compartmentation are more complex.
  
  

That’s why “18 metres” is a guidepost, not a boundary.You could have a 17.5-metre building with complex uses that still triggers enhanced oversight.

Equally, a 19-metre student block might qualify — even if the floors are compact — because of the way the residents use the building and the level of dependency involved.

What This Means for London Projects

In London, the vast majority of higher-risk buildings fall into three categories:

1. Tall residential or mixed-use towers — often around Paddington Basin, Canary Wharf, White City, and Battersea.
   
   
2. Converted or repurposed structures — like older office buildings being turned into flats.
   
   
3. Care, student, and health facilities — smaller in height but with more complex evacuation or dependency risks.
   
   

Each one brings its own regulatory hurdles — particularly under Gateway 2 of the Building Safety Act, when design approval from the BSR is mandatory before construction can start.

This is where many projects stall.Architects without the right Principal Designer competence (as defined under the BSA) find their projects delayed — or worse, rejected outright.

That’s why, at Payte Architects London, we’ve built an in-house compliance process specifically for HRBs.

How Payte Architects London Approaches Higher-Risk Buildings

We treat safety as a design discipline, not an afterthought.Every HRB project we take on goes through a framework led by Teddy, our in-house Principal Designer, who ensures that compliance, design intent, and safety strategy all align from day one.

Our process includes:

• Early-stage risk mapping — identifying how the design interacts with structure, fire, and services.
  
  
• Coordinated documentation — drawings, specifications, and safety statements aligned for Gateway submissions.
  
  
• Collaboration with consultants — structural and fire engineers integrated from the start, not brought in later.
  
  
• Regular review checkpoints — internal design “gateway moments” before anything is submitted to the Regulator.
  
  

We’ve found that by embedding the Golden Thread — the continuous record of design and safety information — right into our workflow, approvals go smoother and the design stays coherent.

And that matters, especially in West London, where most HRBs sit within dense, mixed-use neighbourhoods.When you’ve got commercial units below, residential above, and shared access routes throughout, coordination is everything.

The 18-Metre Rule Is a Trigger, Not a Limit

Here’s the real takeaway: the 18-metre rule isn’t a line between “safe” and “unsafe.”It’s a trigger for deeper scrutiny — a prompt for design teams to prove competence and take responsibility.

In practice, the same principles apply even below that threshold.If your building involves multiple uses, complex evacuation, or large numbers of residents — you should still be applying the HRB mindset.

It’s about culture as much as compliance.

As Teddy says:

“You don’t design safely just because the law says you have to. You do it because it’s the right thing — and because it makes the building work better for everyone inside.”

A Note from Simon Baker, CEO & Founder

“I think we’re entering a new era in London architecture — one where competence is measured by clarity, not credentials.

The 18-metre rule was never meant to be a barrier. It’s a signal. It tells us which buildings demand the highest level of care.

At Payte Architects London, we’ve built our practice around that principle — that design and safety are inseparable. And honestly, I think that’s what good architecture has always been about.”

— Simon Baker, CEO & Founder, Payte Architects London

Final Thoughts

The 18-metre rule might be the headline, but it’s not the whole story.A Higher-Risk Building is defined by people, purpose, and complexity — not just numbers on a drawing.

As London continues to grow upward and inward, this clarity matters more than ever.Developers, designers, and owners all share one responsibility: to design and build spaces that are safe, compliant, and human.

At Payte Architects London, we help clients do exactly that — blending strong design with rigorous safety oversight, so projects move forward with confidence and care.

📞 Tel: +44 20 3984 8501

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