Technical Booklet G Resistance to the Passage of Sound·Page 39·2.57
External cavity wall closure at eaves
External cavity walls must be closed at eaves level with a cavity stop such as mineral wool, avoiding rigid connections between wall leaves.
Where there is an external cavity wall, the cavity should be closed at eaves level with a cavity stop e.g. mineral wool (see Diagram 2.14). Note – A rigid connection between the inner and external wall leaves should be avoided. If a rigid material is used, then it should only be rigidly bonded to one leaf. See BRE BR 262, Thermal Insulation: avoiding risks, Section 2.3.
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