Be guided by design

Schools have always been noisy places, and it is perhaps not surprising to learn that teachers form a disproportionate percentage of those who attend hospital clinics with voice injuries. Prolonged use of the voice coupled with a frequent need to shout above the din of the classroom is often cited as the cause of these injuries. Children are also affected by noise.

Dr Bridget Shield, Professor of Acoustics at London South Bank University, said: “There is a great deal of evidence now concerning the effects of noise on pupils. Both external noise and classroom ‘babble’ affect children’s performance on verbal and non-verbal tasks in the classroom.” She said many studies have demonstrated the detrimental effects of aircraft noise, particularly on reading.

The problem of noise in the schools has steadily increased. Changes in teaching practices and use of electrical equipment in the classroom have all contributed to the increase in noise levels.

Legal context for BB93

While guidelines for acoustics in schools have been in existence since the 1970s none have had the force of law. Such guidance did not become mandatory until 1 July, 2003, when Building Bulletin 93: Acoustic design of schools (BB93) was incorporated into Part E of the Building Regulations 2000 (as amended). These regulations apply only to construction in England and Wales. The internal acoustic environment of new and refurbished schools must comply with the specification of acoustic performance contained in section 1 of BB93. The acoustic performance criteria specified in BB93 are not retrospective and therefore existing schools need not undertake action to comply. However there may be instances where a designer would use BB93 to upgrade existing school spaces in order to meet the special educational needs of children or the requirements of the Disability Discrimination Act.

The status of BB93 is different in Scotland. Its use is not mandatory. The statutory environmental requirements for schools are contained in the School Premises (General Requirements and Standards) (Scotland) Regulations 1967 (as amended). These regulations require acoustic conditions in Scottish schools to be ‘appropriate’ to the use for which that part of the school has been designed. While the regulations do not define what is meant by ‘appropriate’, the Scottish Executive document: School design: optimising the internal environment, acknowledges BB93 as a source of good acoustic standards for schools.

In the case of Northern Ireland, the Department of Education for the province directs new schools be constructed, subject to certain relaxations, in accordance with the guidelines contained in BB93.

Type of noise addressed by BB93

School premises comprise a wide range of different acoustic spaces each of which presents its own acoustical challenge. The bulletin aims to promote good conditions for speakers and listeners, and prevent interference from noise emanating from other parts of the school.

The length of time noise takes to decay in a space is one property that influences the ease with which speech can be understood. This property is referred to as reverberation and spaces that are too reverberant can be noisy and make the process of teaching and learning difficult for both speakers and listeners.

Conditions in the classroom can be made worse if sound resistance of doors, walls, floor and ceilings is poor. Noise can enter the classroom from surrounding areas, such as staircases, corridors and practical rooms. Noise levels in these areas may be high because of long reverberation times or the activity is naturally a noisy one.

The bulletin contains recommendations for mid-frequency reverberation times (Tmf) and indoor ambient noise levels (LAeq, 30 min (dB)) for finished but unoccupied and unfurnished rooms. It also specifies performance standards for airborne and impact sound insulation between rooms.

Room use determines solution

Corridors, stairwells and other circulation spaces can be very reverberant and can be the source of high noise levels. Treating the ceilings of these spaces with sound absorbent material can reduce reverberation and hence reduce noise levels overall. The amount of sound absorption needed can be calculated from one of the two methodologies contained in section 7 of Approved document E – Resistance to the passage of sound.

The classroom is the core-teaching environment in most schools. It is important that classroom acoustics support learning and teaching activities. The surface finishes in many classrooms are acoustically hard and reflect sound easily. These reflections combine to increase the reverberation time of the room. The increased reverberation reduces speech intelligibility and makes learning difficult not only for those with a hearing impairment but also for other pupils.

The upper limit set by BB93 for indoor ambient noise levels for unoccupied classrooms is 35dB, with mid-frequency reverberation times of less than 0.6 seconds for primary school classrooms. For secondary school classrooms the figure is 0.8 seconds or less. For classrooms designed specifically for use by those with impaired hearing the reverberation times are much shorter at 0.4 seconds or less.

Assembly halls in schools are used for many activities. Such halls often have hard surfaces that reflect sound well and as a consequence such halls have long reverberation times and suffer from poor acoustics. The introduction of surfaces that absorb rather than reflect sound can improve matters greatly. The bulletin specifies the indoor ambient noise level for such spaces when unoccupied should be no more than 35dB and reverberation times should be in the range 0.8-1.2 seconds.

Music rooms in schools perhaps present the greatest acoustical challenge. Not only do they need to have longer reverberation times than rooms of a comparable size used for speech but the noise level created by musicians must not be allowed to escape and interfere with surrounding rooms. For performance or recital rooms BB93 gives a range of between 1.0 and 1.5 seconds with an indoor ambient noise level of no more than 30dB. The performance for sound insulation between such rooms must have a sound reduction index (Rw) of not less than 45dB.

The devil is in the details

A survey conducted for the National Deaf Children’s Society concluded that up to 40% of new schools fail to meet the legal standards. Product substitution, poor quality craftsmanship, and ineffective site supervision all contribute to the problem. Attention to detail when implementing acoustical provisions is extremely important.

A suitably qualified consultant should be appointed to undertake the design, and to inspect the work as it proceeds. This will ensure simple mistakes are not made, and time and money is not wasted on remedial or unnecessary work. In addition the likelihood of the project failing to meet the performance standards of BB93 will be greatly reduced.

The building bulletin suggests a competent consultant is likely to be a corporate member of the Institute of Acoustics. The institute is the professional body for those working in the areas of acoustics, noise, and vibration and members are well qualified and bound by a code of conduct.

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