Insulating between and outside the studs – timber frame with masonry outer leaf
Before cutting Kooltherm K112 to slot between the studs, the gap between each stud should be carefully measured to ensure a snug fit. The insulation boards can then be cut to size with a fine-toothed saw.
The insulation should be installed flush with the outer face of the studs and treated softwood battens fixed in place to prevent the boards from moving within the cavity. To limit air leakage, any gaps or penetrations through the insulation layer – such as plug sockets – should be filled with a flexible sealant or a combination of flexible polyurethane foam and flexible sealant or equivalent. A vapour control layer should also be installed on the inner face of the stud. This can be provided by vapour check plasterboard, polythene sheeting or with a couple of coats of drywall sealer.
Timber frame systems come with a layer of oriented strand board or plywood fixed to the external face of the studs, along with a breather membrane. A second, continuous layer of insulation can then be fitted externally to the breather membrane. The insulation boards should be restrained in accordance with the timber frame manufacturer’s guidance. If this guidance is unavailable, insulation boards should be lightly butted to maintain continuity and fixings carefully lined up with underlying timber studs, headrails and sole plates.
Large-headed galvanised clout nails can be used to hold the insulation boards in place before they are tied into the masonry leaf with an appropriate timber frame wall tie.
