External Walls
Due to the diversity of possible wall constructions, combined with variations in project specific acoustic criteria, outlining standardised solutions for this general area is problematic. For this reason it is preferable that the details for a particular project are discussed with our technical department. However, as many of the common lightweight wall constructions are discussed in separate sections, the following guidance predominately pertains to masonry wall structures.
Masonry wall structures, in general, inherently offer a relatively good sound reduction performance due to their high surface mass. However, substantial variations still exist between different generic constructions. On the assumption that an improvement in sound reduction performance is required (beyond that provided by the base wall structure), the following techniques may prove helpful.
As masonry structures offer a high surface mass, the potential for improvement by the means of applying further weight directly to the structure is minimal. The ‘mass law' indicates that for every doubling of the surface mass an improvement in sound reduction performance of approximately 5dB can be expected. In consequence, useful gains can only be achieved by the application of linings that are spaced away from the base structure and ideally are mechanically isolated from it. This technique permits modest gains even when the surface mass of the added lining is a different order of magnitude to that of the base masonry structure.
In addition to improving the sound reduction performance of the external wall, these types of internal linings also assist in improving ‘flanking transmission'. This is a phenomenon where sound is transferred to other areas within the building by transmission through a common building element (an external wall being such an example). Flanking transmission should not be confused with airborne transmission through a separating element itself. In some situations flanking transmission can be of great importance and indeed can limit the achievable overall sound transmission loss, irrelevant of how well the actual separating element performs.
The following items detail two common techniques for improving the SRI of a masonry wall by means of an applied internal treatment.
