Noise impact assessment

Posted: 2nd December 2022

What is a Noise Impact Assessment?

The Local Authority Environmental Health Officer will often request a noise impact assessment (or NIA) to support a planning application.  This guide discusses why a noise impact assessment is required and what your NIA report should contain.

A Guide to Noise Impact Assessments

What type of developments need a Noise Impact Assessment?

Planning applications for most noise-generating and noise-sensitive developments will require a noise impact assessment.

Noise-sensitive developments typically refer to new residential dwellings, hotels, schools, hospitals, or other buildings where the occupants might expect to rest, sleep, or study.  Noise-generating development is a broad term.  It includes new roads, railway or similar infrastructure development, bars/restaurants, fitness gyms, and other entertainment venues, industrial facilities, through to a single air conditioning condenser being installed to an existing property.

What are the stages of a Noise Impact Assessment?

The exact methodology for a specific noise impact assessment will depend on the type of noise source that is being assessed.  Assessments are conducted using different British Standards or guidance documents; however, the typical process will include:

1. Carrying out a background sound level survey to determine the existing (baseline) noise levels in the area.
2. Computer modelling is used to predict noise levels from noise-generating development.
3. Measured or calculated noise levels will be compared against the existing noise climate to determine the potential impact on existing or future occupants.

What Standards are commonly used?

Which British Standard or the guidance documents used for a noise impact assessment will depend on the type of source being assessed.  The most used Standards include:

• BS 8233:2014 – This Standard is used to assess noise from transport sources (road, railways, and aircraft) or anonymous noise – sources without a specific character.  The Standard includes guideline sound level criteria for inside residential properties.
• BS 4142:2019 – Noise from industrial and commercial sources are typically assessed using the methodology in BS 4142.  This can range from a power station or large factory to a single air conditioning condenser.  There are several types of noise which are excluded by the standard, including music, people, domestic animals, construction and demolition, vehicles travelling on public roads/railways, and recreational activities.
• The Institute of Environmental Management & Assessments’ Guidelines for Environmental Noise Impact Assessment compares both the change in sound level and character in the acoustic environment.

A good quality noise impact assessment will also consider local planning policies along with national policies including the National Planning Policy Framework (NPPF).

How is the noise survey conducted?

The noise survey procedure is again dependent on the exact focus of the noise impact assessment.  Large infrastructure projects will require baseline noise monitoring to be conducted at several positions over an extended period.  Smaller developments may only require one or two measurement positions with surveys conducted over 24-48 hours.

The aim of the background noise survey is to establish the current sound level and the character of the acoustic environment in the vicinity.

The consultant will use a calibrated Class 1 sound level meter, set up at a position equivalent to the noise-sensitive receptor.  The ambient (LAeq), background (LA90), and maximum (LAfmax) sound levels will be recorded.  Depending on the assessment method other indices and octave or third-octave band frequency spectra may also be stored.

Results of the survey will be downloaded and assessed on computer analysis software.

Calculations and noise modelling for Noise Impact Assessments

All noise impact assessments will include some form of acoustic calculations.  Environmental noise propagation is typically calculated using the method in ISO 9613.  Smaller or more simple developments may be assessed using numerical computer calculation models.  More complex and larger assessments are usually conducted using noise mapping software.  ACA Acoustics use iNoise noise mapping software which is based on ISO 9613 and the associated ISO 17534 quality standard.

The effect of distance between the source and receptor, acoustic absorption, reflections, screening, and other acoustic corrections are accounted for.  The software produces coloured 2D or 3D noise maps.  These can assist in developing appropriate noise mitigation measures (e.g., barriers or the acoustic design of building façade elements).  Noise maps are also useful in conveying information to the EHO and planning officer.

What should be in a Noise Impact Assessment report?

A high-quality noise impact assessment report should include all relevant information to allow the Local Authority EHO to make an informed decision on the acoustic impact of the proposed development.

The NIA report will typically include:

• Discussion of relevant local and national planning policies.
• Appropriate Standards and other guidance documents which have informed the assessment method.
• Results and methodology for the baseline sound level survey.
• The outcome of computer calculations and noise modelling, including details of any assumptions used in the model.
• Assessment of the impact the development will have on the existing acoustic environment.
• Mitigation measures that will be required to avoid significant adverse impacts on noise-sensitive receptors.

How ACA Acoustics can help with your Noise Impact Assessment

We have extensive experience in undertaking noise impact assessments.  These range from an individual bar or restaurant through to large residential developments and industrial facilities.  We provide a high-quality noise impact assessment report which will be suitable to submit to the Local Authority in support of your planning application.

Please call us at your local office number or use the contact form to find out how we can assist in making sure the acoustic impact of your development is correctly assessed at the earliest stage.  Our experienced consultants are looking forward to discussing your project in more detail.

Posted By:Rob Cant