Assessing the situation

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.

What kind of noise is it?

Noise in buildings is usually assigned to one of three classes:

Airborne sound
Sound such as voices, TV or stereo sounds. The source does not strike or vibrate against the structure of the building.
Structure-borne sound
Sound that is generated when some object in contact with the structure vibrates and so generates noise. Examples: elevators, washing machine, plumbing noise.
Impact sound
Sound that is generated when some object strikes the structure of the building. Examples: door slamming, a hammer blow, footsteps.

What kind of construction is involved?

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.

What is the sound rating for the construction?

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.

How much sound attenuation do I need?

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.

Are there any obvious faults?

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:

Has the wall been properly caulked?
Sometimes caulking fissures or gaps can make enough of an improvement to the sound isolation.
Are there unsealed electrical outlets?
Gaps around electrical outlets allow sound to pass through. The cover plate is an ineffective barrier. Common draft excluders behind the cover plate will usually be enough to deal with this. The seriousness of such leaks depends on the location of the electrical outlets and on whether there is sound-absorbing material in the cavity. Sealing is simple and does no harm.
Are service penetrations sealed?
Plumbing and air supply ducts might provide easy paths for sound, either around the edges because of inadequate sealing or by transmission along the inside of the duct.