Edge sealing requirements for party wall thermal bypass

Where edge sealing is adopted to address the party wall bypass it is essential that the edge sealing is effective in restricting air flow into the cavity and that it is aligned with the thermal envelope. Sealing is required at the top, the bottom and vertically. Although effective edge sealing may be incorporated as part of a cavity barrier which is provided as a fire stop, a cavity barrier on its own may not be effective in restricting air flow into the cavity. In order to use the reduced cavity wall U-values in Table 2.3 (0.2 or 0.0 W/m2.K) it will be necessary to demonstrate that the design adopted is likely to be robust under normal site conditions. For example, in a room-in-the-roof design, the insulation layer is likely to follow the sloping roof to a horizontal ceiling and then continue at ceiling level. In such a case it is important that the party wall cavity seal follows the line of the insulation in the sloping roof and horizontal ceiling sections. In the case of flats, the sealing system should follow the line of party floors and other party structures as well as the main thermal envelope.