Full or partial cavity insulation of external walls

A full or partial fill insulating material may be placed in the cavity between the outer leaf and an inner leaf of masonry subject to the following conditions – (a) the suitability of a wall for installing insulation into the cavity should be determined either by reference to BRE Report 262 Thermal insulation: avoiding risks or following the calculation or assessment procedure in current British or CEN standards. When partial fill materials are to be used, the residual cavity should be not less than 50 mm nominal; or (b) a rigid (board or batt) thermal insulating material incorporated into the wall should be the subject of current certification from an appropriate body or a European Technical Approval and the work should be carried out in accordance with the requirements of that document; or (c) other insulating materials inserted into the cavity after the wall has been constructed should have certification from an appropriate body and be installed in accordance with the appropriate installations code. The suitability of the wall for filling is to be assessed before the work is carried out and the person undertaking the work should be registered under an Approved Installer Scheme that includes an assessment of capability. Alternatively the insulating material should be the subject of current certification from an appropriate body or a European Technical Approval. The work should be carried out in accordance with the requirements of the certification and the operatives should be either directly employed by the holder of the certification or employed by an installer approved to operate under the certification; and (d) when the cavity wall of an existing building is being filled, special attention should be given to the condition of the external leaf of the wall, e.g. its state of repair and type of pointing. Guidance is given in BS 8208-1. Some materials that are used to fill existing cavity walls may have a low risk of moisture being carried over to the internal leaf of the wall. In cases where a third party assessment of such a cavity fill material contains a method of assessing the construction of the walls and exposure risk, the procedure set out in paragraph 6.17 may be replaced by that method.