BB93 Acoustic Solutions for Schools

Understanding BB93 in Schools

Recent studies have shown that many classrooms have poor acoustics. As a result, children with normal hearing are often unable to make out what is being said in class.

While adults will guess at missing words, children find it much harder to fill in the gaps and their educational development can suffer.

Before 2003, Part E of the Building Regulations did not apply to schools. It now includes schools within its scope.

It also requires sound absorption to entrance halls, corridors or hallways in multiple dwellings such as flats.

All school buildings are now subject to detailed design checks and on-site inspections by building control officers.

Section 1 of Building Bulletin 93 (BB93) describes the Specification of Acoustic Performance.

This section gives the performance targets for compliance with the Requirement from Part E of the Building Regulations 2003 (as amended):

Each room or other space in a school building shall have the acoustic conditions and the insulation against disturbance by noise appropriate to its normal use.

The aims of BB93 are to:

a) provide a regulatory framework for the acoustic design of schools in support of the Building Regulations
b) give supporting advice and recommendations for planning and overall school design
c) provide a comprehensive guide for architects, building services engineers, clients and others involved in the design of new school buildings.

Unfortunately, a large number of classrooms in the UK currently suffer from very poor acoustics.

Poor acoustic conditions in the classroom increase the strain on teachers’ voices as most teachers find it difficult to cope with high noise levels.

This often leads to voice problems due to prolonged use of the voice and the need to shout to keep control. Recent surveys in the UK and elsewhere show that teachers form a disproportionate percentage of voice clinic patients.

Historically there have been a number of factors preventing good acoustic design and Building Bulletin 93 addresses these issues. Pressure on finances has meant in the past that acoustics came low on the list of design priorities.

The acoustic design will now have a higher priority as it will be subject to building control. The overall objective of the performance standards in section 1.1 is to provide acoustic conditions in schools that:

a) facilitate clear speech communication between teacher and student and among students
b) do not interfere with study activities.

Due to limitations of space in this article we will focus on solutions to reduce reverberation in study spaces and sound absorption in corridors, entrance halls and stairwells.

Why are some rooms acoustically poor?
There are three main reasons why rooms may be acoustically poor for speech:

a) too reverberant for the speech sounds produced in them
b) too noisy because of weak resistance offered to the penetration of noise from outside or from nearby rooms
c) shaped so that the speakers are more or less screened from all or part of their audience.

Effect of reverberation on speech
Part of the sound from a teacher, the direct sound, passes directly to the ears of his/her pupils.

Another part travels to the room surfaces and is reflected, eventually reaching the pupils’ ears from many directions at close intervals; this is called reverberant sound.

If there is too much reverberant sound, the pupil is still receiving the reflected sounds of previous syllables when he is trying to cope with the direct sound of later syllables. The two then interfere, and speech is difficult to understand.

The amount of reverberation is usually expressed as the reverberation time, which is the time taken for the sound to die away after its source has stopped.

It is determined by the volume of the space and its capacity for sound absorption and is defined as the time taken for the sound to decay by 60 decibels.

It may vary from half a second in an ordinary living room to 8 seconds or more in a large assembly hall or gymnasium.

A classroom or teaching space with a long reverberation time of several seconds will cause syllables to be prolonged so that they overlap and hence degrade speech intelligibility.

Adding acoustic absorption panels or tiles will reduce the reverberation time and will improve speech intelligibility.

Building Bulletin 93 specifies the reverberation times required for various teaching spaces ranging from classrooms to assembly halls.

Amount of acoustic absorption required
In classrooms and other rooms for speech, large amounts of fixed acoustic absorption are often required particularly where rooms have high volumes, as often occurs in older buildings.

It is advisable to contact our technical department so that the correct amount of sound absorption can be calculated for the space in question.

Distribution of absorbent panels and tiles
The location of acoustic absorption within a room is important. The traditional calculation of reverberation time assumes that the absorbent surfaces in a room are reasonably evenly distributed.

If this is not so, the reverberation time equation is not valid and undesirable local variations in the acoustics can occur, particularly in large rooms or halls.

Large areas of acoustically reflective material can also lead to echoes, focusing and standing waves.

Where absorption occurs only on the floor and ceiling, for example in a solution employing acoustic ceiling tiles and carpeted floors, users may experience an over-emphasis on sound reflections in a horizontal plane.

This often leads to ‘flutter echoes’ between walls, which results in the actual reverberation time being considerably longer than the calculated reverberation time.

A much better solution, especially in large rooms, is to distribute some of the absorptive paneling on the walls.

Hearing impaired pupils
Many hearing impaired pupils make use of low frequencies below 500Hz to obtain information from speech.

Therefore, for hearing impaired pupils to be included in classes alongside pupils having normal hearing, special care should be taken to minimise low frequency indoor noise levels.

Suitable sound absorbing panels offering very good sound absorption at low frequencies should be considered for these areas. Speak to our technical team for advice.

Corridors, entrance halls and stairwells
The Building Regulations Approved Document E also contains guidance on the addition of sound absorption to common areas in buildings containing multiple dwellings, such as blocks of flats.

This gives two methods for the application of sound absorbers.

Method 1
For entrance halls, corridors or hallways, a Class C performance absorber to cover an area equal to or greater than the floor area to be applied (usually) to the ceiling. Our ceiling tiles/absorbers all meet this requirement.

For stairwells or a stair enclosure, the requirement is to cover an area of at least 50% of the ceiling with a Class C absorber of the combined area of the stair treads, the upper surface of the landings (excluding ground floor) and the top ceiling area.

Method 2
This needs detailed acoustic calculations to assess the amount of absorption required – please contact our technical department for assistance with this method.

Assembly halls

These spaces are increasingly used in schools for a wide range of activities and not confined to just assembly halls. Typical uses are drama, parents’ evenings, meetings, exams, sports, audio/visual presentations etc.

These halls usually have hard, sound-reflective surfaces and suffer badly from poor acoustics. Floors are normally wooden or vinyl; walls are normally plastered or timber clad and ceilings are concrete, plasterboard or timber boarded.

A typical solution is to line high level wall surfaces with our F/G or acoustic panel system acoustic panels and if necessary add some further acoustic panels on the ceiling.

A reverberation time of 0.8 to 1.2 seconds is required for assembly halls.

Sports halls

Sports halls are designed with robust and impact resistant constructions as these spaces will need to suffer years of long-term use.

Due to the need for durability, the interior surfaces tend to be chosen for those purposes.

The floors are usually timber sprung, the walls are painted blockwork and the ceilings are plasterboard or profiled steel cladding.

All these hard surfaces combine to produce an ‘echo chamber’ in the building. This makes conveying instructions to pupils very difficult as speech is unintelligible.

A solution to this problem would be to line the walls at high level, normally from door head upwards, with our F/G or acoustic panel system. These are robust as they will withstand impact from indoor footballs and come pre-decorated in a range of 40 standard colours.

A reverberation time of less than 1.5 seconds is required for sports halls.

For further information on sports hall acoustics and suitable products click here

Classrooms

These are the most numerous teaching spaces in any school and hence the most important.
They cater mainly for around 20–30 pupils, one teacher and one teaching assistant.

These rooms are reliant on the spoken word without any electronic amplified system. Therefore the intelligibility of the spoken word is paramount. This is particularly important as some of the children in the class may have a hearing impairment.

The surfaces of classrooms can vary from school to school. Some classroom floors have carpets, some have timber, some have vinyl or other surface finishes.

Others may have a  combination of these. Walls in modern schools are generally plastered but older schools may have brick or painted blockwork. Ceilings may be concrete, plasterboard or even suspended ‘office’ type  ceilings.

An acoustic solution to these rooms can be the installation of our F/G or acoustic panel systems  in a horizontal band at high level on the walls and/or other sound absorbers applied to the ceiling.

A reverberation time of less than 0.6 or 0.8 seconds is required for classrooms.

For further information on classroom acoustics and suitable products click here

 MUSIC ROOMS

Of all the spaces in a school, music rooms will present the greatest acoustic challenge is because they generate the highest  levels of sound and are the most sensitive to noise intrusion to and from other areas.

As space in schools is always limited, these rooms tend to end up smaller than desired. Not only are high sound levels a problem but the frequency of sounds generated can contain a significant amount of lower bass frequencies.

Parallel walls should be avoided by angling some of the walls to diffuse the sound and reduce standing waves.

Particular attention should be paid to the doors as they are generally lightweight. Normal acoustic treatment would be to install our profiled melamine tiles on the walls and ceilings.

If extra low frequency absorption is needed  then we can supply a range of acoustic bass traps and corner wedges. Our acoustic door sets can be used to deal with sound transmission problems.

A reverberation time of less than 1.0 second is required for music classrooms and less than 0.8 seconds for small practice or group rooms.

For further information on rehearsal/music practice room acoustics and suitable products click here

Dining rooms

These rooms are designed to take a lot of punishment and all the surfaces are hard and cleanable.

Floors are normally ceramic tiles or vinyl or timber. The walls are mainly plastered and painted. The ceilings are a mixture of surfaces such as plasterboard, timber boarding, metal decking or other surfaces.

Compared to other school spaces like classrooms, drama rooms, halls etc., children entering dining rooms will be making more noise as they are in a less formal area and can relax and play and joke with their friends during their lunch break.

Hence dining rooms tend to be very noisy and the clatter of cutlery and screeching of chairs is very noticeable as well as the general verbal noise from the children.

In some situations our hanging baffles will be suitable but often acoustic ceiling tiles and panels on the walls are preferred.

A reverberation time of less than 1.0 seconds is required for dining rooms.

Music recording rooms

BB93 requires sound insulation through walls of music rooms. All spaces used by students except music rooms require a minimum sound insulation value of Rw 30dB for door sets.

Note should be made of the term ‘door set’. This comprises the door leaf, door frame, acoustic and fire seals, door threshold and hinges. It is the correct combination of all these components that will achieve the desired acoustic performance.

We have a timber acoustic doorset rated at Rw 35dB and steel acoustic doorsets with acoustic ratings as high as Rw 54dB which therefore meet the sound sound insulation performance of the BB93 standards.

Music practice rooms require a minimum sound insulation value of Rw 35dB.

For design and specialist product enquiries, consult our qualified acousticians on 01730 269572.