In our experience it is never safe to assume because the architect has specified high performance walls, windows and floor/ceiling assemblies that this will definitely pass sound testing in London. There are many other issues to consider such as the onsite workmanship and sound insulation at junctions to prevent noise flanking.
When the construction assembly is tested in the lab, it is also certified and the installation techniques are described in detail. Unfortunately it is not always possible to replicate the exact conditions on the site compared to the ideal conditions within in a lab setting, which is a far more controlled and scrutinised environment. This is why an allowance of minus 4-5 dB should usually be accounted for due to onsite construction.
Unfortunately, sound will usually find the weakest link through construction materials via noise flanking. For instance, construction workers sometimes run the inner envelope walls straight through the whole building elevation. Unfortunately, even though the partition walls may be acoustically robust, it doesn’t stop sound travelling from unit to unit via the continuous wall behind – i.e. along the inner wall of the building envelope and this can easily result in you project failing its sound test in London. In this instance the envelope wall should stop and return along the dividing wall partition providing a cavity or sound insulation break in the envelope wall and between flats.
If you would like more information in regards to acoustic design or sound testing in London, please contact us now at firstname.lastname@example.org or call us on 01525 303905.