Cold Bridging (also known as Thermal Bridging or Heat Bridging) occurs in a building where there is a gap in the insulation such as a join or corner or where a structural element spans across thermal insulation (for example in timber frame panels). The effects of this are not immediately visible, but over time and in the dampness of the UK, it can destroy the fabric of the structure and have secondary effects such as damp and mould growth.
In timber structures and frames, panels can be faced with insulation on the inside and outside faces, thus overcoming issues associated with insulation applied only between the timber studs or within the frame panels.
The U values shown in the diagrams above are achieved using a 120mm layer of solid petrochemical based insulant between the 140mm studs within the panel. The insulation is fitted within the panels in a factory environment improving quality control and ensuring a precise fit. The panels are also of a reasonable width of approximately 203mm so that they do not encroach in your living spaces. The panels reduce costs for heating, improve air tightness and greatly reduce cold bridging. These diagrams show how the panels are constructed but they can be adapted to suit particular requirements.
Installing a service void to the internal side of the timber frame helps to ensure that the insulation, vapour control layer and air tightness membrane are left undisturbed. This helps to prevent any air movement within those layers as convection will significantly reduce the performance of the insulation.
To meet the requirements of the accredited construction details (ACDs) insulation should be taken below the Damp Proof Course (DPC) so that thermal bridging does not occur below the DPC.
The windows should be installed within the timber frame & insulation layers to help eliminate thermal bridging. However, if windows are fitted to the external face then the window reveals need to have a layer of insulation fitted to further assist in reducing cold bridging. The fire sock around the windows also acts as a thermal insulator. Air sealant tape is applied around the windows for air tightness.