Planning Noise Survey’s
APT Sound Testing undertakes hundreds of planning background noise surveys every year throughout the England and Wales. Prior to us visiting site to undertake a planning noise survey, we check the criterion set out by the environmental protection team the appropriate way to carry out a noise impact assessment.
Prior to the EA making any decisions in regards to the likely impact of a development, it will usually be necessary to have a full understanding of the existing noise in the vicinity of the receptor. This is achieved by carrying out a background noise survey or ambient noise levels survey over periods of time representative of the times and days when the noise source will be operational i.e. over a 24 hours period. Depending on the assessment method used, the baseline will usually be determined by measuring the LA90 or the LAeq. In practice we usually measured both simultaneously using our latest class 1 acoustic analysers.
The LA90 is the ‘A’ weighted noise level exceeded for 90% of the measurement period. Typically this is called the background noise level if it relates to a period when the noise source is not operational the ‘A’ weighting is a correction applied within a sound level meter to adjust the response of the meter to match the response of human hearing at different frequencies. This approach is used to exclude short-term noises, such as a vehicle passing, from the measurement value, leaving only the underlying or background noise. The LAeq is as an average noise level over the measurement period.
Potential Noise sources and times of operation A detailed knowledge of the noise source (or in the case of a proposed development, the likely noise source) is essential as you will need this information to complete the planning noise survey. This is because noise levels are of less importance than the amount by which they exceed the baseline noise and the times or days of operation. Where the noise source already exists, data from the survey should give information about levels, frequency content and variability during and between days. Levels may be measured at the proposed receptor location or calculated later from source data at a different location. If the proposed development will create a source of noise, the consultant we usually need to obtain manufacturer’s data for proposed equipment, times of operation and working practices. Alternatively noise from the same equipment could be measured elsewhere.
Determining the impact of noise via a PPG24 or BS4142 noise survey Noise impact is determined using a variety of methods, all of which will rely on comparing noise levels at a receptor against absolute noise level criteria or against existing baseline noise levels. Generally one of following two approaches is used:
- Where the proposal is for a development which will introduce an industrial type noise source, or where a receptor in a new development may be affected by this type of source, it is usual to assess impact by comparing the noise level, after making corrections for certain attributes of the noise, against background noise levels at the receptor (existing or proposed). The council expects that, at the receptor, noise from the source is a certain amount below existing background levels. Typical cases include new equipment in a business, an air conditioning unit or an extract and fan serving a restaurant. This is known as the BS4142 noise survey methodology.
- Sometimes the impact does not depend on a comparison between source evels and baseline levels. For example, a proposed housing development near an existing road, where generally the impact is determined by establishing whether the absolute levels due to the source are acceptable. This is known as the PPg24 noise survey methodology.
Noise mitigation measures Development proposals which are inherently noisy may include mitigation measures in the original scheme. However, the need for further mitigation may be necessary when the impact assessment indicates that the acceptability criteria are exceeded. Either way noise mitigation, or reduction measures, should be considered in the assessment in demonstrating how the acceptability criteria will be achieved and this should be detailed within the planning noise survey.
The most effective measures will be those which reduce noise levels at source, rather than in transmission or at the receptor. However, in situations such as where the proposal is for new housing near existing sources of noise, it will not be possible to reduce source noise levels. Where the proposal will introduce a new noise source, it is good practice to reduce levels at source as far as possible. This can be actioned by considering other mitigation measures, for example:
- Reduction of noise at source – Using equipment or systems with lower sound power levels is highly effective and can avoid the need for other more costly and intrusive mitigation options. Noise impact can be lessened by reducing total running times or by shifting operations to less sensitive times of the day. Such practices may be the best, or only, method of control which would permit the development to proceed. The use of acoustic silencers and enclosures around the source may also be effective at reducing the need for other mitigation methods.
- Reduction of noise in transmission – The simplest way to reduce noise once emitted is by increasing the distance to receptors. This is not always possible but if it can be achieved reductions of 3-6dB per doubling of distance can be expected.
Siting of plant and equipment within an industrial site should be as far away from sensitive receptors as possible i.e. residential properties. Alternatively a new housing development may be designed so that properties are set back from a noise source, compared to other less sensitive parts of the development, such as landscaping.
In many cases, a properly calculated buffer zone between source and receptor will represent the most cost effective noise control measure. Where land is scarce, or distance alone provides insufficient noise mitigation, an earth bund or other noise barrier may be useful, especially if combined with other control measures. To be fully effective, the height and location must be carefully calculated and for noise sensitive developments it may first be necessary to take additional measurements to record predominant noise frequencies. In general to be effective most barriers will need to cut off line of sight between the source and the receptor.
Apply Noise Reduction at receptor In many instances this may be the only option to reduce impact where a noise sensitive proposal is located in a busy urban area and where the applicant has restricted access to land for the construction of a barrier, in this instance acoustic upgrades can be made to the building façade and/or the proposed plant specification.
In our experience the way a development is designed can be an effective mitigation tool if the buildings main facades can be designed to face away from the main noise source. This usually works in two ways; firstly, the building itself acts as a noise barrier providing sheltered external areas; secondly, if noise sensitive rooms are located on the sheltered side of the building, the impact will be reduced by the reduction of weaker building acoustic elements such as windows and doors.
Where no other options are available, improving the sound insulation of a building facade can be effective in reducing internal noise levels. However, often it will be necessary to provide acoustic treated mechanical ventilation to avoid the need to open windows in warm or humid weather or at the very least acoustic trickle ventilation to the windows.
If you would like more information on planning noise surveys for your development, please contact us at firstname.lastname@example.org or phone us on: 07775623464