BS 4142 is the British Standard used to assess the impact of industrial and commercial noise on nearby sensitive premises. It works by comparing the rating level of a specific noise source (adjusted for acoustic character) against the prevailing background noise level at the nearest receptor. A difference of around +10 dB or more indicates a likely significant adverse impact. Around +5 dB indicates a likely adverse impact. At or below background indicates negligible impact. Most local planning authorities require a BS4142 assessment when new commercial or industrial premises are proposed near residential properties, or when fixed plant and equipment is being installed. The 2019 amendment (BS4142:2014+A1:2019) introduced important updates to methodology that all current assessments must reflect.
What is Impact Sound?
Sound travels through buildings in different ways, by both airborne sound and structure-borne sound. One form of structure-borne sound is known as impact sound.
What causes impact sound?
Common occurrences such as people running, dropping objects and even walking cause impact sound. This has an effect not only on the rooms that are below but also rooms either side as the sound travels as a result of the vibration from the impact.
Impact sound is usually stronger as it travels through a floor and will reduce slowly. It’s a tricky type of sound to prevent, as it travels in different ways. Vibrations from the impact cause the sound to travel through ceilings and walls.
How can impact sound be reduced?
There are various ways that impact sound can be reduced or even prevented in buildings. One way is to utilise soft carpets and pad cushions that are thick, so that middle to high-level frequencies can be significantly reduced.
Underlay that is made of rubber, fibreglass or foam is particularly effective when it comes to reducing impact sound, as these materials can absorb the energy produced on impact, minimising how far the sound travels.
Hanging resilient mounts, spring ceiling hangers and sound clips can reduce the transmission of sound by separating different sides of a building, allowing each side to vibrate in isolation upon impact.
Another way in which impact sound can be reduced is by applying layers for soundproofing. The way in which this is done is by applying the compound between two fixed materials, which prevents vibrations caused by sound from travelling through a building.
Installing suspended ceilings or raised floors is another way in which buildings can be constructed to improve impact sound. This works by absorbing sounds upon impact so that sounds will be minimised for the areas of a building below the ceiling.
Impact sound: an issue to be tackled during development
When designing a building, it’s important that steps are taken to minimise the risk posed by impact sounds. Of course, many impact sounds are due to everyday occurrences and it’s inevitable that they will happen, but by using some of the techniques outlined here, buildings can be constructed in a way that reduces the risk of unnecessary and extensive impact sound.
The transmission of impact sound is measured in a specific area of a building itself by using a tapping machine that hits a particular surface to generate sound in a neighbouring space, which is then monitored. This gives an indication of how likely it is that impact sound will be prevalent inside a building, so that the appropriate steps can be taken to reduce the level of impact sound that may occur in future.
NOVA Acoustics Ltd have a published a huge amount of Free Sound Insulation Design Advice here, including soundproofing floor and wall systems, as well as how to approach acoustic detailing and flanking sound. Click through to our Sound Insulation Design Advice section. Or if you need Sound Testing or Consultancy, give us a call to chat with one of our friendly consultants.
Related article: What is Structure Borne Sound? And how can it be reduced?
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