So, your building failed its TM52 overheating assessment.
Now what?

Take a breath. You’re not alone and this isn’t a deal-breaker. In fact, a lot of buildings fail TM52 the first time. The real trick is knowing what to do next and acting quickly before it delays your build or planning application.

At Gradwell Group, we’re here to help you move from failure to fix with practical, cost-effective solutions that make sense. Let’s walk you through what it means, why it happened, and how we help get your project back on track fast.

What does a TM52 failure actually mean?

The TM52 assessment, developed by CIBSE, is designed to measure how likely a non-domestic building (like a school or office) is to overheat during warm months especially when there’s no air conditioning.

It checks whether the indoor temperature exceeds set thresholds, using real-life UK weather data and thermal modelling. If two or more of its criteria fail, your building doesn’t meet thermal comfort standards.

But that doesn’t mean you’ve failed overall it means there’s still work to do.

Why buildings fail TM52: The usual suspects

There are a few key reasons buildings don’t pass first time. Some of the most common we see at Gradwell Group include:

• Too much glazing without proper solar control
  
  
• Poor natural ventilation windows don’t open wide enough or cross-ventilation is missing
  
  
• Lightweight construction without enough thermal mass
  
  
• Overcrowding or high internal heat gains from computers and lighting
  
  
• South-facing rooms with no shading or blinds
  
  

Sound familiar? Don’t worry most of these can be adjusted without a full redesign.

What should you do if your building fails TM52?

Step 1: Read the report carefully

Your assessment report should tell you:

• Which zones failed
  
  
• How badly they failed
  
  
• Which of the three criteria were breached
  
  

Step 2: Talk to your consultant

At Gradwell Group, we never just hand over a failed report and walk away. We’ll always:

• Talk you through the results
  
  
• Recommend quick, practical tweaks
  
  
• Rerun the model after changes
  
  

And yes, we include multiple iterations in our price no surprise charges for re-checking your design.

Step 3: Apply smart design fixes

Often, it only takes a few well-placed changes to go from fail to pass.

Some of our go-to strategies include:

• Adding ventilation louvres or increasing window openings
  
  
• Fitting external shading like overhangs or vertical fins
  
  
• Changing glazing specs to reduce solar gain
  
  
• Switching materials to boost thermal mass
  
  
• Adjusting occupancy hours or internal layout

How fast can you fix a TM52 failure?

In most cases, within 3–5 working days.
Our team can update the model and rerun your TM52 as soon as we receive revised drawings or design notes.

If you’re up against a planning deadline let us know. We’ll prioritise it.

Get a quote or speak with our team

Why does TM52 matter so much?

Overheating in buildings isn’t just uncomfortable it’s a real health risk, especially for schools, hospitals, and offices. The UK Government’s Part O Building Regulations now require buildings to show they’ve considered thermal comfort during design.

A failed TM52 might delay planning or block sign-off unless you show that you’ve made meaningful improvements.

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What makes Gradwell Group different?

We’re not just here to tick boxes. We’re here to help you:

• Understand the issues clearly
  
  
• Fix them efficiently
  
  
• Avoid costly rework later
  
  
• Submit a planner-friendly report that’s ready for approval
  
  

Our experts work with architects, developers, schools, and engineers across the UK, and we’re proud to offer fast turnarounds, fair pricing, and honest support every time.

FAQs: 

1: Can I still submit planning if my building fails TM52?

Not usually. Most authorities will ask for a compliant report before granting approval.

2: Do you charge extra to rerun the model after changes?

Nope. Our pricing includes unlimited iterations until your design complies.

3: Is TM52 just a London thing?

No. While the London Plan makes it mandatory, many councils across the UK are adopting similar overheating policies.

4: Do you offer fixes or just tell me what’s wrong?

We do both. We’ll guide your design team through cost-effective solutions that actually work.

Final thoughts: 

Failing TM52 isn’t a sign your project’s in trouble. It’s a useful checkpoint to help you design better buildings and at Gradwell Group, we’re ready to help.

Identifying the problem to refining your layout and submitting a polished report, we’ll keep things simple, fast, and on budget. Need help now?  Contact our overheating assessment team and we’ll sort it no fuss.