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Sound advice

technical & practice

Designing for good acoustic performance in schools is now compulsory. Here we examine some of the main issues

Since 1 July, acoustic design of schools has been mandatory. In the past, the use of Design Notes and Building Bulletins (BB) was as guidance only, and was often treated as something that would be nice to comply with, if only it didn't cost too much. As a consequence, a number of schools have been designed with little or no regard to such guidance or with guidance applied incorrectly. The result has sometimes said to have had an adverse effect on children's learning and staff welfare.

1The Department for Education and Skills has set out to change this by replacing BB87 2Part A with BB93 3, forming Part E4 of the Building Regulations (2003). Acoustic design of schools therefore becomes standardised and regulated under the Building Control process. Generally, standards under BB93 are higher than in BB87, for the following reasons: to improve the quality of the learning and teaching environment; and to facilitate integration of children with Special Educational Needs (SENs) into mainstream schooling. It is commonly acknowledged that children with SENs are more easily distracted by noise and require lower reverberation times within learning environments.

So this is all a step in the right direction, but at what cost? Some suggest that the increase in cost of a school under BB93 compared with BB87 could be up to 10 per cent, depending on the complexity of the design. Also, with the format of sound reduction and absorption fixed more rigidly, there are fears that innovation and flexibility within schools may be stifled (most prominently in open-plan teaching areas).

As with the onset of any regulatory document after a period when only guidance has existed, the construction industry is facing a large problem with Private Finance Initiative projects that have been designed up to Invitation to Negotiate stage (ITN) under BB87 guidance, but now require modifying for compliance under BB93. This is causing significant disruption to cost plans and programmes. So what changes have been made to BB87? And have all the problems been ironed out?

BB93 opens with a note to strongly recommend the use of an acoustic consultant. Even though I am biased, this is a worthwhile consideration because BB93 is not the 'simple but comprehensive guidance' claimed in the Consultation Document. While this could be seen as good news for acoustic consultants, together with the increased workload from the requirements of Part E, it is putting great stresses on a profession already suffering from a lack of qualified staff.

Noises off

As stressed repeatedly within BB93, its objective is to 'provide acoustic conditions in schools that (a) facilitate clear communication of speech between teacher and student and between students; and (b) do not interfere with study activities'.

Indoor ambient noise levels are specified for each space within a school. This level is defined as the contribution of the effect of external activities (transportation, industrial noise, etc. ) and building services (including natural ventilation).

Unlike BB87, this does not include noise from adjacent areas within the school, as this should be controlled adequately by the selection of sound insulation properties of walls and floors based on 'activity' and 'tolerance' levels. While this should be relatively fail-safe in most school situations, areas of very high noise production, such as music rooms, are still likely to cause disturbance, which will be discussed below.

Two other factors excluded within the ambient noise level are noise produced by machinery and equipment within a particular space (eg fume cupboards, drills etc) and that generated by rain on roofs. The former is self-explanatory and the usual precautions for noise at work need to be considered. The latter, however, is a subject frequently raised in the acoustics world. The problem with rain noise is that it is so difficult to standardise and quantify. Acousticians like to be able to have a set way of testing, based on a laboratory ideal; rain, on the other hand, is infinitely variable, and furthermore is messy.

Research into rain noise and its quantification is still a subject of international discussion, and we are probably still two years away from any agreed guidance. In the meantime, rain noise should be 'considered', but no formal guidance is given. There is a danger of rain noise being treated in the same way as floor impact noise in BB87, which was 'considered' (particularly in PFI contracts) then quickly ignored.

Noise tolerances

A comprehensive set of room classifications is given in BB93, with an 'activity noise', 'noise tolerance' and upper ambient noise level being defined for each. The set of classifications is more comprehensive than in BB87 and should therefore reduce some of the confusion previously caused by interpretation. However comprehensive the list, there will still be times when interpretation has to be applied; it is imperative, though, that the end user be made aware of these interpretations to avoid confusion later.

Criteria for airborne sound reduction between adjacent areas have been expanded and made more onerous than under BB87. The method of rating these values has also changed, from D w, which could only be accurately quantified when the rooms were fully finished, to D nT(Tmf, max), w , which is an adaptation of the factor used to quantity residential sound reduction. The latter can be used to quantify the sound reduction of an element without absorbent finishes in place (eg prior to installation of suspended ceilings), which provides greater versatility in testing throughout the contract; this will allow testing to be carried out before it is too late, to allow architects/contractors to action any changes needed.

Music rooms continue to cause problems. These are generally the sources of highest noise levels within a school, and are yet sensitive to intrusive noise, making the sound reduction requirement very high. This gave rise to the debate whether to increase the sound reduction in music areas to =60dB, allowing flexibility in locating such areas. However, the emphasis on workmanship, detailing and construction cost of such elements affects buildabilty and does not guarantee that disturbance would not be caused when pupils are playing trumpets or drums. Therefore, the middle ground has been chosen, whereby sound reduction similar to that of a residential party wall or floor, in combination with sensible space planning (eg locating music rooms away from other areas, using storage rooms as a buffer etc) should be implemented. In my opinion, in whatever case, the end user must be fully consulted in the design of such areas and made aware, in lay-man's terms, of the acoustic implications.

In order to reduce noise break-in to classrooms from corridors, a criterion has been given for doorsets. This would appear to preclude the use of standard doors with perimeter and threshold seals, unless accompanied by a laboratory test certificate, and will have a severe cost implication.

Designers must also be mindful of the ability of some smaller or disabled children to open doors having good acoustic seals.

Knock-on effects

The requirement of schools to have doors within walls dividing adjacent classrooms is actively discouraged, as this renders the overall sound performance between spaces too low. If this is still required by teachers for convenience and security, the designer should make the acoustic implications clear to the end user.

Impact sound within multiplestorey buildings was sadly overlooked in BB87, but is addressed comprehensively under BB93. Criteria are similar to those in residential situations and will have a major impact on the design of dividing floors. No longer will carpets and linoleum be sufficient (due to their low performance, which reduces with wear), but methods such as floating screeds will be required.

Reverberation times within school areas are dealt with in great detail. In general, requirements are more stringent than under BB87, for reasons discussed above. It is likely that all classrooms will now require mineral fibre ceilings having Class A absorption (precluding the use of plasterboard or lower-performance tiles), or the use of perforated liners to lightweight metal roofs.

4There is no lower limit for reverberation times within classrooms - therefore, in these spaces, the more absorption the better. Care should be taken in music and drama areas, however, to not reduce reverberation too far, and to provide diffusion to sound where necessary.

Open-plan teaching areas have always caused problems, and will continue to do so. Many teachers and educationalists are strong supporters, but open-plan areas can be very problematic acoustically. Logic dictates that, if we know that high levels of sound reduction are required between cellular classbases, how can we allow adjacent classes to operate with nothing except fresh air between? To this end, BB93 requires full justification for the use of open-plan teaching areas, including a comprehensive computer model showing that the Speech Transmission Index between teachers and pupils within a space is at minimum 'good', if not 'excellent'. This will likely make designers think twice about using open-plan teaching areas, as it will be very difficult to make them 'work'.

During and at the end of contracts, acoustic testing to support the design is 'recommended'. Under the wording within Part E4 of the Building Regulations, it is not possible to make testing compulsory. However, testing is the only method of proving that design criteria has been met or otherwise.

In conclusion, BB93 is a necessary and welcome step in improving the standard of learning and working environments within our schools.

There is no doubt that standards need to improve, and this document goes a long way to facilitate this. Many designers and contractors will inevitably complain about the increased costs, but this will have the greatest impact on those who have been providing schools until now that have not even been in compliance with BB87, whether by design or by poor workmanship.

Andrew Parkin is principal acoustic consultant at R W Gregory, Birmingham and member of the BB93 Review Panel. Tel 0121 456 1560 or email aparkin@rwgregory. co. uk

References

1.Classroom Acoustics, MacKenzie D and Airey S, Heriot Watt University Department of Building Engineering and Surveying, Edinburgh.1999.

2.BB87 - Guidelines for Environmental Design in Schools (Revised 2003).

3.BS93 - Acoustic Design of Schools.

4.Class A Absorption, as defined in BS EN ISO 11654:1997, denotes the highest category of sound absorption for speech frequencies.

To reduce the Reverberation Time (RT ) within a classroom to below 0.6/0.8secs, a major surface area within the room will usually need to have high sound absorption.

Modified plasterboard (eg Gyptone) will not provide enough absorption if used as the only absorbent source.

Given that the lower the RT the better (hearing impaired classrooms being down to 0.4 secs), a Class A mineral fibre absorber would be the most appropriate solution.

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