Connect the leaves of a cavity masonry wall only where necessary by double-triangle ties as described in BS 1243:1978 Metal ties for cavity wall construction, and spaced as required for structural purposes (BS 5628-3: 2001 Code of practice for use of masonry. Materials and components, design and workmanship, which limits this tie type and spacing to cavity widths of 50 mm to 75 mm with a minimum masonry leaf thickness of 90 mm). Alternatively, use wall ties with an appropriate measured dynamic stiffness for the cavity width. The specification for wall ties of dynamic stiffness, kXmm in MN/m with a cavity width of X mm and n ties/m2 is n.kXmm<113 MN/m3.
Note: In external cavity masonry walls, tie type B may decrease the airborne sound insulation due to flanking transmission via the external wall leaf compared to tie type A.
2.21 Measurements of the wall tie dynamic stiffness, kXmm should be carried out according to BRE Information Paper, IP 3/01.
2.22 The number of ties per square metre, n, is calculated from the horizontal and vertical tie spacing distances, Sx and SY in metres using n = 1 / (Sx.Sy). Example: For horizontal and vertical tie spacing distances of 0.9 m and 0.45 m, n is 2.5 ties/m2.
2.23 If kXmm is not available for the required cavity width, it is acceptable to use available kXmm data for X mm values less than the required cavity width to calculate n.kXmm.
2.24 All wall ties and spacings specified using the dynamic stiffness parameter should also satisfy the Requirements of Building Regulation Part A - Structure.
2.25 The separating walls described in this section should be used between corridors and rooms in flats, in order to control flanking transmission and to provide the required sound insulation. However, it is likely that the sound insulation will be reduced by the presence of a door.
2.26 Ensure that any door has good perimeter sealing (including the threshold where practical) and a minimum mass per unit area of 25 kg/m2 or a minimum sound reduction index of 29 dB Rw (measured according to BS EN ISO 140-3:1995 and rated according to BS EN ISO 717-1:1997). The door should also satisfy the Requirements of Building Regulation Part B - Fire safety.
2.27 Noisy parts of the building should preferably have a lobby, double door or high performance doorset to contain the noise. Where this is not possible, nearby flats should have similar protection. However, there should be a sufficient number of flats that are suitable for disabled access, see Building Regulation Part M - Access and facilities for disabled people.
2.28 A wall separating a habitable room or kitchen and a refuse chute should have a mass per unit area (including any finishes) of at least 1320 kg/m2. A wall separating a non-habitable room from a refuse chute should have a mass per unit area (including any finishes) of at least 220 kg /m2.
2.29 The resistance to airborne sound depends mainly on the mass per unit area of the wall. Constructions
2.30 Three wall type 1 constructions (types 1.1, 1.2, and 1.3) are described in this guidance.
2.31 Details of how junctions should be made to limit flanking transmission are also described in this guidance.
2.32 Points to watch
Resistance to the passage of sound 18