The reason steel needs a thermal break is because of its high heat conductivity. Without the thermal break it means that when the inside of an external wall is warm compared with the outside, sufficient heat will flow through the steel stud to cool the inside surface of the wall, causing condensation and compromising the wall’s insulation rating.
This conductivity is often portrayed as being a weakness with steel. However, it is one of its greatest strengths. It means that when the thermal break is in place, all the steelwork on the inside of the thermal break remains above the temperature at which condensation from moisture in the wall cavity will occur – which ensures long term durability of the stud.
The outside of the timber stud will attract condensation during winter and, with the resulting increase in moisture content, movement that damages linings and potential long-term durability problems. This occurs in timber irrespective of the weather tightness of the external cladding.