What is a Thermal Break, and When Should You Use One?

A thermal break can improve the energy efficiency of a building by reducing heat loss. When should one be used, and how does it relate to regulations?


16 Aug 2023


Simon McAuliffe

A view from a glazing link

In any good sci-fi film centred around space travel there will, at some point, be a scene in which characters pass through an airlock. That airlock accommodates a transition from one environment – ‘in here’ – to another – ‘out there’ – safely.


Back on planet Earth, a kind of airlock exists as a physical barrier – around the edges of many modern windows and glass doors. It is known as a thermal break or a thermal barrier, and its purpose is to regulate the internal temperature of a building by minimising the heat exchange that is allowed to take place.


Insulation within your walls does an excellent job of keeping our homes warm in winter and cool in summer, but windows and doors – where the building’s envelope (its perimeter) is much thinner – allow hot or cold air to bypass the insulation and flow far more freely.


Aside from making rooms rather uncomfortable, the flow requires longer periods of heating to reach the desired temperature, increasing both your client’s energy bills and their CO2 outputs. 


The Paris Agreement states that global emissions must peak before 2030 in order to limit temperature rises to 1.5 degrees centigrade (above which the consequences are catastrophic and very likely irreversible).  Pressures to meet emission reduction targets and improve affordability of energy bills in the current cost of living crisis have led the government to introduce Part L – and several ‘Approved Documents’ – of the UK’s Building Regulations, requiring all new homes built from June 2022 to produce 31% fewer carbon emissions than the acceptable level before that date.


The governmental emphasis on energy efficiency might be the reason that you’re seeing the term ‘thermal break’ more and more. It is, after all, a very effective way to reduce heat loss, often by as much as 27%!


To understand how one works and for which applications it would be suitable, we need to return to basics for a moment. 

A glass extension with its doors open

What is a thermal break?


A thermal break refers to a material with low thermal conductivity placed between two pieces of material with high thermal conductivity. Doing so prevents the high-conductivity material from acting as a thermal bridge between the inside and the outside of a building.

The application of a thermal break and the materials used to contribute to one can vary considerably, but let’s take a window as an example. Its frame might be aluminium. As a result of the aluminium’s high conductivity, heat from the inside of your building can easily be lost to the outside due to it.

The addition of a low-conductivity material – often polyamide – sandwiched between the aluminium stops the heat exchange taking place, or at least reduces it significantly.


Other benefits of incorporating a thermal break into your project


A thermal break doesn’t just keep energy bills down, reduce your client’s carbon footprint, and make rooms more comfortable during the temperature extremes of a British summer or winter.

There are two other distinct benefits we think it is important to highlight:


Reduced condensation


Condensation, as we all know, occurs when warm, moisture-laden air meets a surface at a lower temperature, transforming water vapour into (liquid) water.

Without a thermal break, the hot air from inside your home is exposed directly to the cold glass standing between it and the outdoors. This sudden, drastic change in temperature makes the water vapour in the hot air condense, steaming up your windows. This can increase the chance of mould and damp issues within your home, which pose health risks such as respiratory problems and infections.

In short, a thermal break can ensure your view stays crystal clear all year round, keep you warmer using less energy (goodbye sky-high bills!), and prevent unnecessary health risks.


Improved structural integrity


When glass heats up, it microscopically expands. The opposite is true when it is cooled. This ‘breathing’, as you might visualise it, can be quite substantial if the temperature fluctuates from very hot to very cold in a short space of time, putting stress on your glazing which could result in cracks and even shattering. 

(You can read our article about nickel sulphide inclusion, characterised by sudden and unexpected shattering here.)

The presence of a thermal break reduces that fluctuation, thus minimising expansion stress and the chances of your glazing becoming compromised as a result.

But stepping away from the concept of temperature, if only briefly, glazing is often expected to support substantial amounts of weight. The material used to create a thermal break is usually a very strong one, contributing to a frame’s rigidity and making it more resistant to warping or bending.

Now that we understand what a thermal break is and the benefits it can contribute towards your next project, let’s turn our attention to how one might relate to UK Building Regulations, specifically Part L.

A lovely glass extension - even in the rain
A brightly lit kitchen

How does a thermal break relate to Part L of the UK’s Building Regulations?


Part L of the UK’s Building Regulations is specifically concerned with the increased conservation of fuel and power in dwellings. The government’s justification for focusing on this area is illustrated by the fact that 17% of all UK emissions are produced within a domestic setting by things like gas boilers which provide our heating and hot water.

The Approved Documents associated with Part L provide helpful advice to builders and contractors about how they can reduce the number of thermal bridges (areas heat can escape through via high-conductivity materials). Arguably, from a glazing point of view, the best way to reduce energy inefficiencies would be through the installation of windows and glass doors that have a thermal break around the edge.  

The presence of a thermal break reduces the amount of energy required to heat a home, thus reducing the emissions that are produced as a result. It’s a win-win situation for both your client AND the planet.

A brightly lit reception area

When should you use a thermal break?


A thermal break should feature as part of any glazing product that is to be used on the outside of a building – or where heat is likely to be lost from one space to another.

You might, for example, install one within an exterior window as part of a 17th-century farmhouse renovation to keep the winter cold out. Alternatively, in educational facilities, where common areas and classrooms are constantly exchanging heat, a thermal break can contribute to temperature regulation, making the environment a far more comfortable one.

 Its versatility and effectiveness are what make a thermal break so popular within the world of architecture, but there is one final question that we should ask ourselves…


Will a thermal break compromise the aesthetics of a project?


Absolutely not. Thermal breaks can be designed to be discreet and blend seamlessly with the overall aesthetics of a project.

Just take a look at any of the images used throughout this piece. Each one has a thermal break built into the design, maximising efficiency while ensuring a clean, consistent appearance.

Thermal breaks offer an aesthetic solution to sustainable living. Want to know more? Talk to us today.