How should rigid insulation be installed in a cavity wall?

Rigid insulation should be installed directly against the concrete in a cavity wall to ensure maximum thermal performance and energy efficiency. When rigid insulation is placed against the concrete, it effectively minimizes thermal bridging, which can occur when materials of different thermal resistances are in contact. This installation method also helps to prevent moisture infiltration into the wall assembly. By placing the insulation in direct contact with the concrete, it creates a continuous insulation layer that enhances the overall insulation effectiveness of the wall.

The other methods do not promote optimal insulation performance. For instance, placing insulation too far from the exterior or allowing space for an air gap could compromise the insulating properties and lead to increased energy costs. Similarly, a loose fit for expansion may allow for air movement and reduce the intended effectiveness of the insulation material. Therefore, the most efficient technique is to ensure the insulation is installed firmly against the concrete surface.