Before attempting to improve a wall or floor, it is essential to assess the situation to try to identify the major cause of the inadequate sound isolation. Unnecessary alterations can waste effort or money.
Noise in buildings is usually assigned to one of three classes:
Before any improvement can be considered the construction details must be determined, not only for the party wall (or floor) but also for the walls and floors that abut the party wall. The details of the connection between the walls and floors should be known too, if possible. This information is needed to decide if flanking paths are likely to be a serious problem. Building plans or information from the developer might be available but some visual inspection - if possible - will confirm what has actually been constructed.
Measured STC ratings are for particular constructions measured in a laboratory may be available from manufacturers of materials such as gypsum board, fibrous absorbers, concrete block etc. Approximate values are given on this web site. The values are estimates of what would be measured in the test facilities at the Institute for Research in Construction, (IRC) of the National Research Council (NRC), Canada. There are many research reports freely available from the IRC Publications page.
Building codes typically require that a party wall or floor have an STC of at least 50. The rating that is more relevant to a building occupant is the apparent STC. A survey commissioned by NRC suggests that an ASTC of 55 will satisfy most occupants. However, each situation is different. The degree of annoyance depends on the level of noise from the neighbout, the sound attenuation between the homes, the background noise in the homes, and the sensitivity of the occupants.
To get the maximum attenuation from a wall or floor, there should be no unnecessary penetrations or leaks. A small hole in a wall can seriously degrade the sound isolation. Some things to check are: