It is the sound produced when an object impacts or interacts with a surface, such as footfall on a floor, falling objects, or mechanical vibrations.

When an impact occurs, the impact’s energy is conveyed to the surrounding structure in the form of vibrations. These vibrations can propagate through the building components, including floors, walls, and ceilings, and emit sound on the other side. The resulting impact noise can be heard in adjacent spaces or rooms as an abrupt, transient sound.

To a certain extent, building regulations in the UK protect adjacent dwellings from impact noise by imposing criteria that needs to be achieved (as required in Approved Document E – see a later blog in this series).

There are numerous variables that can influence impact noise transfer:

Source Characteristics: The force, weight, and surface area of the object causing the impact can affect the generation of impact noise. Heavier objects or those with a larger contact area can generate more intense vibrations and, consequently, impact noise. An example would be the likely sound transfer difference between a grown adult in stilettos and a child in trainers.

Structural Pathways: The path that vibrations travel through a structure plays a significant role in impact noise transfer. Depending on the construction materials, rigidity, and connection points, structural components such as floors, walls, and ceilings can transmit vibrations differently. In general, harder and more rigid materials transmit vibrations more effectively, whereas materials with greater damping properties can help reduce vibrations. We can mitigate this transfer route by the introduction of resilient layers – for example a resilient top layer can be applied above the floor joists or the use of a resilient ‘bar’ to the underside of a structural floor joists. Both of these elements provide a disconnect between the rigid materials, helping to dissipate the sound structural energy.

Below is an image of a resilient bar – this is often used on the underside of floor joists.

Reverberation time / acoustic characteristics of the receiving space: The characteristics of the space in which the impact noise is received also influence its perception. Impact noise transmission and audibility can be affected by the configuration, surface materials, and acoustic properties of the recipient space. A room with firm and reflective surfaces, for instance, can amplify and prolong impact noise, whereas a room with soft and absorbent materials can help reduce its impact.