What Is an Overheating Assessment?

What Is an Overheating Assessment and Why Is It Required?

With rising summer temperatures and increasingly airtight modern homes, overheating is a growing concern in UK residential developments. To mitigate this risk, overheating assessments have become a key requirement in many planning applications—particularly for new-builds and high-density developments.

But what exactly is an overheating assessment, and why is it essential for your project? In this blog, we’ll explain everything you need to know, including when it’s required, what it involves, and how it supports a more comfortable, compliant, and sustainable home.

🔎 What Is an Overheating Assessment?

An Overheating Assessment is a technical evaluation that analyses how likely a building is to become uncomfortably hot during warm weather. It typically applies to residential dwellings but can also be required for care homes, student accommodation, or hotels.

The assessment uses dynamic thermal modelling (often following CIBSE TM59 guidelines) to predict indoor temperatures based on:

Building orientation
Glazing and shading
Ventilation strategy
Thermal mass
Internal heat gains (appliances, people, etc.)
External climate data

The aim is to identify whether a property is at risk of overheating, and if so, suggest design strategies to reduce that risk.

🏡 Why Are Overheating Assessments Required?

Overheating isn’t just an inconvenience—it’s a health and safety issue. Sustained indoor temperatures above comfort levels can lead to:

Sleep disturbance
Reduced productivity
Increased risk to vulnerable individuals (older people, young children, or those with health issues)

As a result, many local planning authorities now require an overheating assessment as part of the planning submission for certain developments—especially:

Urban areas with limited cross ventilation
Flats with large areas of glazing
Homes with non-opening windows
High-rise buildings

Overheating assessments also help support broader environmental and comfort goals set out in building regulations and energy efficiency policies.

🧪 What Standards Do Overheating Assessments Follow?

Most overheating assessments in the UK follow CIBSE TM59: Design Methodology for the Assessment of Overheating Risk in Homes. This methodology is widely recognised by planning officers and local authorities.

CIBSE TM59 sets out performance criteria to determine if a dwelling is “at risk”. If the simulation fails these criteria, design changes—such as improved shading, different glazing ratios, or enhanced ventilation—will be recommended.

Overheating assessments often go hand-in-hand with other building compliance services like:

✅ SAP Calculations for Part L compliance
✅ SBEM Calculations for non-domestic buildings
✅ Energy Performance Certificates

If your development requires one or more of these, it’s smart to consider an overheating risk assessment at the same time for a holistic design approach.

🧰 What’s Included in an Overheating Assessment?

A typical overheating assessment will include:

Dynamic Thermal Model
A 3D model of the building is created using specialist software like IES or Design Builder to simulate internal temperatures.
Simulation Using Weather Files
The assessment uses current and future climate data (e.g. DSY1 weather file) to evaluate performance under realistic summer conditions.
Ventilation Modelling
Natural and mechanical ventilation scenarios are tested to see how airflow affects internal temperatures.
Shading and Glazing Analysis
Windows, overhangs, and blinds are considered to assess solar gain.
Design Recommendations
If the model fails, the report will offer practical design changes to reduce overheating risk—these may include changes to glazing ratios, window sizes, or ventilation strategies.
Comprehensive Report
A detailed report is produced for submission to planning authorities.

🏗️ Who Needs an Overheating Assessment?

You’ll likely need an overheating assessment if you’re:

A developer working on new flats or apartments
An architect designing a modern dwelling with high glazing
A self-builder creating a home with south-facing windows
A planning consultant needing to satisfy local policy requirements
A housing association creating affordable, energy-efficient housing

If you’re unsure whether your project needs one, we’re happy to advise.

📍 When Should You Carry Out an Overheating Assessment?

The best time to conduct an overheating assessment is early in the design stage—ideally before planning submission. Identifying risks early allows for design tweaks that won’t disrupt the build or require costly revisions later.

Leaving it too late could result in planning refusals or delays.

⚠️ What Happens If Your Project Fails?

If a home is predicted to overheat, planning approval may be delayed until mitigating measures are in place.

Our team can work with you to:

Recommend shading devices or improved ventilation
Adjust glazing ratios or window placement
Integrate passive cooling strategies like cross ventilation

We always aim to find cost-effective, design-sensitive solutions that meet both regulatory and client needs.

✅ How Assessment Hive Can Help

At Assessment Hive, we offer fast, accurate, and affordable Overheating Assessments for projects across the UK. Our service is fully remote and backed by years of experience in building compliance.

Call us on 020 7183 3240
Email us at [email protected]
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