Wednesday, 4 February 2015

BB93 Updates - Lean, Green and much much Clearer

MACH Acoustics aims to lead in the acoustics design of low carbon buildings and open plan teaching spaces, and hence has considerable experience in the design of educational buildings, please see our book ‘Sustainable Acoustics’ found at http://www.machacoustics.com/sustainableacoustics/acoustics-vented-facades.

To achieve the above goal, MACH Acoustics works closely with the Architectural Department at the University of Bath and the Institute of Sound and Vibration, University of Southampton. Currently we are sponsoring a KTP, PhD and two MSc Projects, all linked to the design of low carbon building design.

In MACH Acoustics view, BB93 has been intelligently updated with increased clarity and flexibility towards low carbon and refurbished buildings, whilst providing a more inclusive design approach to pupils within our schools.

Clarity

Clear objective performance requirements are provided in BB93 2014, with many areas being clarified.

For example, the requirements for SEN are significantly clearer, noise levels under natural ventilation and the use of Alternative Performance Standards, have been enhanced and strengthened, with new minimum performance standards being provided.

The challenges in refurbishing buildings have been recognized, with internal noise levels for refurbished projects being relaxed by 5 dB, and sound insulation levels reduced by 5 to 10 dB between spaces, depending upon adjacencies.

An increase of 0.2 seconds in reverberation time has also been provided for non-sensitive teaching spaces. These practical changes will make things considerably easier and encourage the refurbishment of buildings.

Low carbon building design is fundamental to our future buildings, BB93 2014 therefore allows internal noise levels to be increased by 5 dB if natural ventilation is being used, irrespective of ventilation rates. MACH Acoustics research indicates that this could result in 50% more schools being naturally ventilated. To promote cross ventilation, the target across cross ventilators has also been cut back to 32 dB Dnew. This dramatic change will significantly increase the feasibility of using cross ventilation, improving ventilation to teachings spaces and allowing for natural ventilation on noisier sites.

Sound Insulation

Sound insulation has in the main remained unchanged for new builds. The maximum level of sound between exceptionally sensitive spaces has been reduced from 60 to 55 dB DnTw, where this is seen to be a more practical performance standard. Additionally, essential doors between teaching spaces are now allowed, providing a 35 dB door is used.

Reverberation Times

As per sound insulation, reverberation times in the main remain unchanged, with the exception of Sports Halls. The target reverberation time is now a function of its size. Open plan spaces typically gain bad press for their poor acoustics. The tightening and additional new performance requirements relating to speech privacy between work spaces and the reduction in reverberation time, is pleasing to see. These important more stringent changes will result in enhancing the separation between workspaces, reduce occupancy noise levels and enhance communication between teachers and pupils.

Areas of concern

In MACH Acoustics view, BB93 2014 is a significant improvement over the old BB93, providing clearer and possibly more appropriate performance standards. However at this stage, we do not see the need to relax the reverberation times in refurbished buildings, since the Essex Study has shown a clear detriment of increasing reverberation times.

Sports Halls are challenging spaces to design and therefore a clear and detailed calculation process must be provided, such to ensure the on site performance of these spaces.


Finally, with regards to noise ingress, we see that the proposed maximum 55 dBA noise ingress level for the 200 hottest hours of the year, is too lenient, and could result in complaints as a result of communication challenges. The statement relating to the acoustics performance of single sided vented facades and fa├žades to cross vented spaces at 16 and 20 dB, is seen by MACH Acoustics to be simplistic, optimistic and lacking in evidence.
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