As the global pandemic creates a new order across towns and cities, a surge in the number of enquiries regarding sound levels in the conversion of commercial buildings into residential spaces is being reported.

Members of the Association of Noise Consultants (ANC) are seeing a significant increase in enquiries across the UK from architects and builders looking to find the best way to manage noise in urban locations.

ANC member David Garritt explains the key issues involved to achieve the best outcome in the conversion process.

Existing Sound Sources

When looking at a project overall, the first point to consider is that of indoor sound climate caused by external sources.

This needs to be accurately established, through an investigation of the sources of sound at a site to quantify the existing outdoor sound climate.

The types of sound to be considered will be different if the project is permitted development or requires planning permission. Permitted development projects may only have to consider sound from nearby commercial uses, whereas projects requiring planning approval should consider all external noise sources.

Points of reference include BS 8233[1] which contains guidance on internal sound levels caused by relatively anonymous outdoor sources, such as road traffic. The industry guidance document ProPG[2] also provides a recommended approach to the management of noise within the planning system in England.

If the outdoor sound climate is influenced by other sources, for example industrial premises, entertainment venues or fixed plant, then different internal sound criteria may be appropriate.

Criteria may be expressed as overall dBA quantities or frequency (musical pitch) dependent Noise Rating (NR) curves. Control or mitigation at source is desirable if practicable, but this is not always possible. The site may need a BS 4142[3] survey or an assessment to the Good Practice Guide on Noise from Pubs and Clubs[4].

The outdoor sound survey and internal sound level targets can be used to specify improvements needed to the sound insulation of building elevations.

Sometimes existing window casements are being retained and may require secondary glazing, or if new windows are proposed, then a glazing specification can be provided.

The method of ventilation is also important – is the site suitable for natural ventilation with windows open and trickle ventilators, or is a mechanical ventilation system required?

The Association of Noise Consultant’s guide to Acoustics, Ventilation and Overheating[5] is useful here, Approved Document O of the Building Regulations[6] may also apply where there is a risk of overheating. If mechanical ventilation is required, consideration needs to be given to internal sound levels caused by ventilation equipment, and any outdoor noise impact from fixed plant units.

Trickle ventilator specification is also vital. Sound insulation of many building elevations is heavily compromised by basic ventilators that do not offer sufficient sound attenuation when open.

There may be existing internal sources that affect the proposed development. This may be from other buildings that directly adjoin the development, or from existing sources in other parts of the same building.

This sometimes occurs when existing ground floor commercial uses such as bars and restaurants are being retained and the floors above are being converted to residential.

There is also a need to consider structure-borne sound/vibration as well as airborne sound. An example of this would be an extract flue for ground floor eateries that is hard fixed to the outside of the building structure and then transmits sound to the interior of flats on upper floors.

The results of a survey of existing sound climate can be used to assess feasibility, provide acoustic specification for the building, and inform layouts in the pursuit of good acoustic design with maximum commercial feasibility.

By their nature, some of the buildings being used for conversion are in city or town centre locations where a mixture of outdoor sources can affect the development and a multitude of ground floor uses are proposed to be retained, some of which may be in operation and some of which may be vacant or speculative.

ANC members can investigate and quantify all these factors and provide recommendations for mitigation and appropriate construction methods.

The Local Planning Authority may wish to see this before considering a planning application. Sometimes validation tests are required by the LPA before handover and there is a clear implication on the quality of life for future residents, so it is essential to get these things right.

Internal Sound Insulation

Separating walls and floors between flats, and between flats and other parts of the building must meet the minimum requirements set out in Approved Document E of the Building Regulations[7] (ADE). Depending on the use of other areas of the building, a higher minimum standard of sound insulation may be required between the spaces than quantified in this document.

Robust Details or bespoke sound insulation details for the development can be used for greater design flexibility. Sound insulation testing can sometimes be carried out prior to conversion work being undertaken to determine the existing level of performance.

Investigation of existing buildings can be undertaken and tests can be carried out if there are separating walls and floors that will remain intact. Often this is not the case, and an inspection of the undeveloped building construction is undertaken instead.

Sound insulation of proposed construction methods can be analysed for compliance with ADE. If construction proposals are not finalised at the time of the survey, then specifications for constructions can be given.

Consideration of flanking transmission around the edges of walls and floors is important. For example, if a superb new wall or floor is constructed to separate flats, it can be compromised by sound travelling along continuous external ceilings or floors, or through voids that exist above and below ceiling or floor level.

Another flanking example is a timber joisted floor cavity concrete block external walls. If the external wall is lined with dot and dab plasterboard, sound can amplify and travel down the block walls to cause a sound insulation test failure across the floor.

ADE also requires control of reverberation in communal corridors, hallways, and stairwells and there are two methods of compliance.

• Method ‘A’ – fitting a minimum area of sound absorbing panels or ceilings rated Class C or better.

• Method ‘B’ – using calculations to take into account any carpet or other sound absorbing surfaces and so minimise additional treatment, an ANC member can assist with this.

Sound insulation tests is required on the completed building to demonstrate compliance with ADE unless Robust Details are used.

The best way to maximise the likelihood of passing the sound insulation tests is to seek expert guidance before construction starts.  ANC companies can advise on construction proposals, junction details and minimising flanking transmission.

For converted properties, the ANC company can inspect the existing building and indicative test work may be carried out before work starts if the existing building is sufficiently intact.

Advice can be given on reverberation treatments to communal areas, the construction of party structures, and internal partitions and floors to be capable of complying with Approved Document E whilst maintaining maximum commercial feasibility.

Approved Document E states that the sound insulation tests should be performed by a company with third party accreditation such as UKAS, or members of the ANC ADvANCE Registration scheme.

Any company that is part of the ANC ADvANCE Registration scheme has demonstrated competency in undertaking the tests accurately. These companies are subject to an annual audit of a randomly selected test site and must complete periodic witness tests by an ANC examiner. Member companies can give advice on remedial treatments in the event of a test failure.

Once a test has been completed, the results are uploaded to the ANC registration scheme server (www.anc-advance.co.uk), where the results may be checked by the customer and building inspectors, so there can be no doubt as to the official result.

Use of a registered ANC member means that the tests will be accurate, conducted by a competent person, can be independently checked using the web-based scheme and advice can be given in the event of a test failure.

[1] BS 8233:2014 Guidance on sound insulation and noise reduction for buildings

[2] ProPG: Planning & Noise – a joint initiative from the ANC, IOA and CIEH https://www.association-of-noise-consultants.co.uk/propg/

[3] BS 4142:2014+A1:2019 Methods for rating and assessing industrial and commercial sound

[4] Institute of Acoustics Good Practice Guide on the Control of Noise from Pubs and Clubs 2003

[5] January 2020 Version 1.1 Acoustics Ventilation and Overheating Residential Design Guide https://www.association-of-noise-consultants.co.uk/avo-guide/

[6] Overheating: Approved Document O https://www.gov.uk/government/publications/overheating-approved-document-o

[7] Resistance to sound: Approved Document E https://www.gov.uk/government/publications/resistance-to-sound-approved-document-e