2.72 Wall type 2.4 Two leaves of aircrete block with 75mm cavity and step/stagger, plasterboard or plaster on both room faces (see Diagram 2-18)
Example of wall type 2.4
The required mass per unit area would be achieved by using
This is an example only. See Annex A for a simplified method of calculating mass per unit area. Alternatively use manufacturer’s actual figures where these are available.
Note: Increasing the size of the step or stagger in the separating wall tends to increase the airborne sound insulation.
Diagram 2-18: Wall type 2.4 Junction requirements for wall type 2
Junctions with an external cavity wall with masonry inner leaf
2.73 Where the external wall is a cavity wall:
2.74 The separating wall should be joined to the inner leaf of the external cavity wall by one of the following methods:
2.75 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 separating wall type 2.1, 2.3 or 2.4 is used.
2.76 Where there is also a separating floor then the requirement for a minimum mass per unit area of 120 kg/m2 excluding finish should always apply, even when wall type 2.1, 2.3 or 2.4 is used.
Diagram 2-19: Wall type 2.1 and 2.2 – external cavity wall with masonry inner leaf
Resistance to the passage of sound 26