A thermal break is essential to prevent ‘thermal bridges’ between the external cladding and the steel framing.
Though extruded polystyrene was invented in the late 30’s, it has only been available for use since 1954. The performance since then has shown that the product is resistant to most environmental effects and is well suited as an insulating material for buildings. The performance of extruded polystyrene (XPS) over the past fifty years confirms that it does meet the requirements of Clause B2 (Durability) of the Building Code.
Maintaining the thermal resistance of a wall assembly in buildings is a requirement needed to meet Clause H1 of the New Zealand Building Code. This requirement especially applies to any part of a steel framed building that provides living space as part of the building’s use.
Extruded polystyrene (XPS) is of very low density, being about one ninth that of typical dry pinus radiata. The product has a low co-efficient of expansion and low fire ignitability index making it suitable as a thermal break. It is impervious to water and nearly impervious to moisture vapor
How to Install XPS
The product is placed over studs, top and bottom plates, nogs and any point where the framing penetrates the insulation. It can be glue-fixed using a polystyrene safe adhesive or screw-fixed with a wafer head screw. The wall wrap is then laid over the thermal break, before the cladding is installed.
Care must be taken to not over tighten the screws used to fix the cladding to the steel framing, and this is especially the case with corrugated metal sheeting. The drill clutch must be set to avoid over tightening of the screws.
Below is the Nation Association of Steel Framing (NASH) N11 house insulation guide v2.2, which gives all the acceptable options for installing themal breaks.