Noise is taken very seriously these days and many residential developments will be required to undertake a noise survey prior to planning approval. This involves long term noise monitoring and in its simplest form, a baseline noise survey determines the time averaged noise levels for both day (LAeq,16) and night (LAeq,8). With this data alone, the local authorities can make a decision as to whether or not the site is suitable for habitation. Whilst it is almost always possible to insulate against external noise with enough sound insulation, it is also recognised that residents have a right to open windows without excessive noise ingress, and that living in constantly noisy environments can have serious health implications.
ProPG is a relatively recent document, published to provide guidance on, and regulate residential noise surveys to a common standard. A ProPG assessment identifies the noise risk of a site which if too high, triggers a more thorough noise risk assessment of the site, encouraging the exploration of various noise control measures such as building layout and orientation, to minimise the noise exposure of future residents. This all comes under the banner of ‘Good Acoustic Design’.
External amenity noise will also be assessed if required; the following passage is taken from WHO Guidelines for Community Noise :
“To protect the majority of people from being seriously annoyed during the daytime, the outdoor sound level from steady, continuous noise should not exceed 55 dB LAeq on balconies, terraces and in outdoor living areas. To protect the majority of people from being moderately annoyed during the daytime, the outdoor sound level should not exceed 50 dB LAeq. Where it is practical and feasible, the lower outdoor sound level should be considered the maximum desirable sound level for new development.”
Residential developments may also require a commercial noise assessment if there are noise generating businesses nearby. An example of this is cafe or restaurant noise, which typically consists of kitchen extraction noise and patron noise generated from customer movements which includes vehicle movements. Whilst customer noise may aﬀect residential facades to the front of the business, the kitchen extraction system may have a profoundly diﬀerent impact upon facades at the rear. In this case it is important that the noises be characterised; vehicle noise and the human voice are noises that are expected to be heard on a street, whilst the constant hum from an extraction fan is not a natural noise that should be audible within a persons garden area, or worst still within a bedroom.
Another example is a large scale residential development near to a factory. This would typically require the inclusion of a BS4142 assessment to identify the industrial noise impact at the residences. Whilst the factory may be large and potentially audible, it may be that the factory is operational through the day time only and that the noise is drowned out by the surrounding road network, in which case there are little or no noise issues.
Environmental Protection Oﬃcers will examine the noise survey report and use the evidence to make recommendations to the planning oﬃcer. The planning oﬃcer may then approve or refuse the planning application, or approve with conditions.
The most common planning condition that we come across is the requirement for a sound insulation scheme. This is the provision of acoustic glazing and acoustic ventilation noise specifications, determined through calculation to ensure BS8233 indoor noise levels are met with windows closed. This is usually a simple process for standard window strategies, but sometimes requires more if window areas are large. In this case, noise ingress is calculated according to ISO 12354, in particular part 3 which deals with the “Estimation of acoustic performance of buildings from the performance of elements — Part 3: Airborne sound insulation against outdoor sound”.
If things get really hairy we’ll use acoustic modelling software to provide an accurate view of how the building reacts to the external noise climate. The modelling considers noise ingress from every building component including building services such as HVAC noise.
Acoustic barrier design is another common tool to reduce noise at a residence, or at least within the external amenity area. This is a fence or a wall that has been specified to achieve a certain level of sound attenuation. Calculations are based on the octave band noise levels incident on the barrier, the sound insulation properties of the chosen material and the transmission path aﬀected by the height of the barrier.
We undertake residential noise assessments every week, and pride ourselves on our surveying and reporting methodologies. We also liaise with local authorities (where possible) to build a good working relationship. This becomes more important as complexity increases as it minimises the potential for un-necessary delay.