“Very proactive and extremely helpful, especially with technical queries. I would not hesitate to recommend and will certainly be using them again in the future.”



Under CDM2015 regs we have found CASS ALLEN to exercise a level of professionalism and due diligence which is second to none. We would therefore definitely recommend CASS ALLEN as our preferred acoustic consultant, for all of our projects.’


SF - Taylor Wimpey South Thames

“I was very pleased with their technical knowledge and professional approach when dealing with a very awkward purchaser as well as the local authority.”


JH, Telford Homes

“Cass Allen went above and beyond to help with the Acoustic planning performance and conditions regarding the Greenwich Creekside project…”


LM, Capita plc

“Good comprehensive reports and advice at all design stages. Very flexible and professional, provided attendance at acoustic cladding tests at short notice.”


DF, Berkeley Homes

“Cass Allen have assisted us on a number of our projects. I’ve been impressed with their thorough and professional approach.”


MT, Lark Energy

What’s New in Acoustics Standards?

There have been wide-ranging changes in acoustic criteria and design guidance of late – these are likely to have major cost and buildability implications for developers.

NPPG – National Planning Policy Guidance

First, NPPG has finally been issued to add some detail to the very vague National Planning Policy Framework (NPPF), which replaced PPG24 ‘Planning and Noise’ in March 2012.

The NPPG contains useful and pragmatic guidance that is primarily aimed at acousticians. It does not contain anything new, but retains some useful advice from PPG24 and brings the guidance into line with the Noise Policy Statement for England (NSPE). The full text can be viewed HERE.

BS8233:2014 – Guidance on sound insulation and noise reduction for buildings

Of greater importance to developers is the revision to BS8233 that came into effect on 28th February 2014.

BS8233 contains guidance and acoustic criteria that are regularly referenced by Planning Authorities when imposing planning conditions and, as such, often dictates the building envelope design and ventilation strategies for developments.

One of the main frustrations with the 1999 version was that it contained two different degrees of acoustic quality, ‘good’ and ‘reasonable’. There was no consensus among Planning Authorities or acousticians as to which quality level was appropriate and, as a result, confusion and inconsistency reigned.

The 2014 version of BS8223 removes the distinction between ‘good’ and ‘reasonable’ and recommends a single standard, which lies somewhere between the two previous standards.

Our experience is that the majority of Planning Authorities, especially those in London, adopted the ‘good’ standard in their planning conditions and so the new version of BS8233 generally represents a relaxation in criteria.

Note 7 to table 4 also allows for a further relaxation in standards of up to 5dB where ‘development is considered necessary or desirable’. In view of current Government Policy towards supporting residential development, it is hard to see a situation where residential development would not be ‘necessary or desirable’. It will be interesting to see how Councils respond to this point.

We would expect that the majority of Councils will require the full standards to be achieved, with the 5dB ‘relaxation’ kept in reserve as a ‘safety margin’ in case of problems during construction. This is similar to the line several councils currently follow – ie imposing the ‘good’ standard but accepting ‘reasonable’ standards at completion on the basis that the quality of workmanship can vary and manufacturer’s performance data is often optimistic.

The 2014 version of BS8233 also brings the design criteria more into line with World Health Organisation guidelines. The changes in internal noise criteria are summarised in the tables below.

BS8233:1999 –


BS8233:2014 –


NOTE 7    Where development is considered necessary or desirable, despite external noise levels above WHO guidelines, the internal target levels may be relaxed by up to 5 dB and reasonable internal conditions still achieved.

Maximum short-term noise events – LAFMax

Another change that potentially has great implications for building envelope design is the removal of the limit of 45dB LAFMax inside bedrooms caused by short term noise peaks (eg aircraft over-flights or train passes). This is a major change because for many urban developments it is this short term LAFMax criterion that determines the building envelope rather than the average noise levels. Again, this is a relaxation in criteria although, the new standard does contain the caveat:

NOTE 4    regular individual noise events (for example, scheduled aircraft or passing trains) can cause sleep disturbance. A guideline value may be set in terms of SEL or LAmax,P depending on the character and number of events per night. Sporadic noise events could require separate values.

It is likely that councils will rely on this note to retain the 45dB LAFMax criterion, which is still contained in WHO Guidelines.

Noise in External Amenity Areas

A further point of confusion in the 1999 version of BS8233 was the advice regarding noise levels in external amenity areas. In many urban developments the 1999 guidance was impossible to achieve. This has been recognised in the new revision and more realistic guidance has now been included. This requires that where design standards cannot be achieved for traditional amenity spaces (eg gardens and patios) then the ‘lowest practical levels’ should be achieved. For non-traditional amenity spaces (eg the small balconies found in many urban developments) it may not be appropriate to impose any noise criteria – especially when it is unlikely that these areas would be used for relaxation. For larger balconies and roof terraces, especially those intended to be used for relaxation, then the same design standards as for traditional amenity areas should be followed, although it is again recognised that compliance with the standards may not be practical.

Unfortunately, the standard is still contradictory on the issue of openable windows and whether it is acceptable to rely on open windows for the provision of purge ventilation and/or the control of thermal comfort where high internal noise levels occur as a result. Our view remains that it is acceptable for internal noise levels to exceed the recommended internal noise levels when windows are opened to provide short-term purge ventilation. However, in noisy areas, where opening windows will result in the standards being exceeded, alternative ventilation should be provided to control thermal comfort over longer periods.

If you have questions on BS8233:2014 and how it might affect your developments, feel free to contact either Patrick Allen (patrickallen@cassallen.co.uk 01234 834859) or Chris McNeillie (chrismcneillie@cassallen.co.uk 01234 834872).


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