Thermal bridges – also known as "cold bridges", "heat bridges" and "thermal bypasses" – aren't unique to curtain walls. They apply to any object where one area has higher thermal conductivity than the surrounding materials. This lets heat pass through, reducing the object's thermal resistance.
In curtain walling, this happens when heat passes through conductive materials such as aluminium and steel. Heat penetrates the insulation layer and gets lost.
When heat bypasses insulation in this way, more energy is required to heat and cool a space. What's more, condensation can build up in the building envelope, leading to mould – not to mention discomfort for the people using the building.
The construction industry knows the importance of insulation. Yet thermal bridging in building envelopes is more common than you might think and is often a nasty surprise to clients.
Here at Wrightstyle, our curtain wall systems are thermally broken, meaning they provide thermal breaks that eliminate thermal bridging. It's one example of why our glazing systems are the best in the business.
The importance of conduction in understanding thermal bridging
Heat transfer happens in three ways: convection, radiation and conduction. In thermal bridging, whether in a curtain wall or other architectural component, heat transfers through conduction.
The rate at which the heat is transferred depends on two things:
The thermal conductivity of the material on each side of the thermal bridge
The difference in temperature between them
Heat follows the path of least resistance through the material with the highest thermal conductivity and the lowest resistance. In the case of curtain walls, this path or thermal bridge can take place in three places:
Structural connections, such as metal fixings and brackets that anchor the curtain wall to the building's main structure
The frame itself – steel or aluminium mullions and transoms that haven't been fitted with non-conductive thermal break material
Junction points, located where the curtain wall connects to the floor slab, roof or cladding. If the junction is inadequately sealed, thermal bridging can occur.
What are the key causes of thermal bridging in curtain walling?
Curtain walls form part of a building's thermal envelope. This is the physical barrier that separates a building's conditioned interior – whether heated or cooled – from the unconditioned outdoors. It includes walls, roofs, floors, windows and doors as well as curtain walls.
Curtain wall frames are often made from aluminium. This is a highly conductive material with a typical thermal conductivity of more than 200 W/mK (watts per meter-Kelvin). In most cases, the frame extends from the building's exterior to its interior, making it prone to thermal bridges.
Here at Wrightstyle, our
curtain wall systems – and indeed all our glazing systems – are made from steel. This is for a number of reasons, including steel's superior strength. It's also, however, because steel is far less thermally conductive than aluminium.
Mild carbon steel has a thermal conductivity of around 50 W/mK, while stainless steel performs better with a thermal conductivity of around 14-16 W/mK. This makes it an ideal choice of material for a curtain wall glazing system.
What are the impacts of thermal bridging?
