Masonry inner leaf mass requirement for external cavity walls

The masonry inner leaf should have a mass per unit area of at least 120 kg/m2 excluding finish. However, there is no minimum mass requirement where there are openings in the external wall (see Diagram 2.8) that are – (a) not less than 1.0 m high; and (b) on both sides of the separating wall at every storey; and (c) not more than 700 mm from the face of the separating wall on both sides. Note – A short length of wall does not vibrate excessively at low frequencies to give flanking transmission.