Thermal Bridging and Thermal Breaks Explained

Thermal efficiency of glazing systems is an important factor to consider when choosing windows and doors for your project.

Windows were once thought to be the cause of huge amounts of heat loss in homes and people tended to be conscious of including too much glazing in their property.

This may have been true 20 years ago, but with modern advances in glazing, windows and doors can be designed to have high levels of thermal efficiency and help to save money on bills.

One way to ensure glazing has a high thermal performance is through the use of a thermal break within the frame. This is especially important in metal framed windows and doors to avoid thermal bridging.

heat diagram showing the thermal energy transfer with and without a thermal break

What is thermal bridging?

Thermal bridging occurs when a conductive material is used to frame glazing systems. The conductive material transfers heat energy from one side of the glazing to the other, causing a significant loss in heat and energy within the home.

Conductive materials, such as aluminium, transfers heat from the internal living spaces to the outside areas and transfers the cold from outside into the internal living space.

Thermal bridging is also a common cause of condensation on the inside of windows and doors as the cool air that gets transferred reacts with the warm internal side of the frame to form condensation.

With condensation can come mould, to avoid the areas around your windows becoming damp and mouldy it is important to make sure your windows do not conduct heat energy and that they are fitted properly by trained and experienced fitters.

steel look sliding glass doors with glazing bars and gable end windows and rooflights
neutral tone living room with a two pane sliding glass door leading to a balcony and a casement window

What is a thermal break?

To avoid thermal bridging, especially with metal framing, a thermal break can be used. Thermal breaks are materials incorporated into the frame to prevent conductive thermal energy loss.

A material with low thermal conductivity is used within the frame to separate the interior and exterior sides of the frames, preventing the conduction of heat energy. Modern thermal break technology tends to see reinforced polyamide bars used within the frames.

Polyamide materials, such as nylon, are ideal for thermal breaks as they have extremely low thermal conductivity. A polyamide thermal break is used in all Sieger external glazing systems as the thermal efficiency of our client’s homes is of the upmost importance.

In a double or triple glazed unit, having a thermal break between the materials helps to increase the thermal performance of the window, door or rooflight.

Thermal breaks decrease the Uf value (thermal value of the frame) and therefore the overall U value, and the lower the U value the better. For more information on thermal performance ratings check out our technical advice article on thermal performance ratings.

Why are thermal breaks important?

Thermal breaks are essential for any external modern glazing system. Thermal bridging can be responsible for up to 30% of a property’s heat loss. This lowers the homes energy efficiency, leading to higher heating bills.

The heat loss is not the only issue, overall having a colder home with condensation and mould can lower the occupant’s quality of life. Being near cold windows in the winter months is extremely unpleasant and can make part of the home unusable.

An added benefit of using a thermal break is that by separating the interior and exterior parts of the frame, this allows for dual colours on some systems. The internal part of the frame can match the internal colour scheme, whilst the outer part of the frame can be designed to blend in with the building exterior.

triangle fixed window and opening rooflights in a loft conversion
cross section diagram showing an aluminium frame with a thermal break and glass with an argon gas cavity
There are many ways to ensure that your windows and doors have a high thermal performance, thermal breaks are just one way.

Sieger also use argon gas cavities and double glazing as standard for all external glazing solutions and many of our products contain warm edge spacers.

All glass used in external Sieger systems can be specified with a low e coating, helping to keep the warmth within the home whilst preventing the suns rays from causing the internal spaces to overheat during the warmer months.


If you have any other questions about the glass used at Sieger or any of our glazing solutions don’t hesitate together in touch with our team.

Call 01494 722 882 or email [email protected]

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