External cavity wall – Hybrid timber frame/ insulating between studs & over sheathing

To achieve higher thermal performance whilst still maintaining minimum frame size, Rockwool recommend the use of their HP Partial Fill slab in conjunction with Flexi product, (fully filling the depth of the studs).

This method of construction will not only minimise cold bridging through the timber frame, but will also improve its acoustic performance.

Installing Flexi

The flexible long edge of the slab allows for the 600 mm wide product to be flexed into the 590 mm space between metal studs or into the 562mm space between 38 mm wide timber studs.

Where studs are spaced at 400 mm centres, 1200 mm x 400 mm wide Rockwool Flexi should be used.

The breather membrane is fixed to the OSB sheathing boardand extended below the lowest timber member (sole plate). Rockwool Flexi is to be applied between timber frames. All material joints must be tightly butted.  A vapour control layer is fixed to the inner face of the studsbefore fixing the plasterboard. The vapour control layer should be fixed according to manufactures instructions. If a plasterboard with a vapour check is used a vapour control layer may not be required. It is important that the vertical joint in the plasterboard lining should coincide with the centre line of the main frame.

Cavity barriers and fire stops should be installed as required to meet the Building Regulations. See Rockwool TCB Cavity Barrier.

Installing HP Partial Fill

After erecting the timber frame, the Rockwool HP Partial Fill slab is fitted to the external surface in conjunction with the brick outer leaf. The brickwork should be tied back to the main stud framing using Helifix InSkew TimTies, which may be driven through the HP Partial Fill slabs into the underlying studs. The HP Partial Fill slabs should be closely butted and retained against the frame using plastic wall tie retaining clips.