Acoustics In Schools and BB93.

In this blog post, we will discuss the importance of good acoustic design within schools as well as typical guidance and acoustic standards used to enable good acoustics in educational facilities.

In order to facilitate comfortable learning in an educational setting the importance of acoustics within the school can not be overlooked. For example, students in a school classroom with excessive noise breaking in from the external environment may find it hard to concentrate. Another example of how poor acoustic design may affect the learning abilities of students or people using the rooms would be a space with excessive reverberation. Excessive reverberation within a learning space/room, or any space for that matter, can cause significant difficulties in understanding speech especially when the student is located at the back of the room. Poor speech intelligibility is often a key symptom of too much reverberation.

In order to combat these common issues schools and educational buildings should be designed to meet the standards and acoustic criteria defined in BB93: Acoustic Design of Schools – Performance Standards.

BB93 Acoustic Criteria Points

BB93 sets out standard acoustic criteria that a school or educational building needs to achieve in order to obtain building regulations sign-off. The criteria outlined in BB93 can be divided into three categories as follows:

-          Criteria for the sound insulation between rooms.

-          Criteria for internal ambient noise levels.

-          Criteria for the levels of reverberation within rooms.

In order to achieve building regulations, sign off for the school building a sample of pre-completion testing is required to ensure the relative criteria for the above three assessment points has been achieved. Given the requirement for pre-completion testing at the end of the build phase of the project, it is vitally important that the acoustic design of any school building is considered at the outset.

School Building Design for Internal Ambient Noise Levels

The internal ambient noise levels within the school building need to be considered. Internal noise levels within any space are typically dictated by two elements; the first is the noise from the external environment breaking into the room via façade elements such as glazing and ventilation vents etc, and the second is noise from mechanical services within the room such as air conditioning.

In order to ensure the noise from the external environment is limited within the building the first step in good acoustic design would be to undertake a noise survey of the site. Once the external noise level has been established appropriate acoustically rated façade elements such as glazing and ventilation can be devised. For example, the internal ambient noise criteria for classrooms is 35 dB. Therefore if a noise survey of the site indicated external noise levels were 70 dB LAeq,t then the façade and roof of the building would need to provide a minimum sound attenuation of 35 dB Rw to ensure that internal noise criteria could be achieved.

As discussed above the ambient noise levels within the school is a combination of both noise from internal services and noise from the external environment. Given this internal noise also needs to be designed to fall below the internal criteria. Typically, significantly lower than the criteria would be required to ensure when cumulative service noise and external break-in noise is measured it falls below the criteria.

Sound Insulation Between Rooms in Educational Buildings

BB93 stipulates criteria for the sound insulation of walls and floors between spaces within educational buildings. However, BB93 does not take a blanket approach with one criteria point for every wall. Instead, the approach to defining appropriate sound insulation criteria is slightly more nuanced with the use of a sound insulation matrix. The sound insulation matrix takes into account the room usage on either side of the wall or floor in order to define a more accurate level of required sound insulation. Firstly, the activity noise within the spaces Is defined and then the noise sensitivity. From this, the matrix is used to define the required sound reduction. In relation to the airborne sound insulation between rooms, the Dnt,w acoustic parameter is used. The matrix form BB93 is outlined below:

BB93 Sound Insulation Matrix

Impact Noise Transmission through the floors is also considered however in this instance a single criterion is outlined for all floors using the acoustic parameter Lnt,w.

Reverberation Time within School Buildings

As discussed above the level of reverberation in a space can significantly affect a person's ability to hear speech and affect their ability to concentrate, two important factors for students in an educational setting. Given this BB93 outlines specific reverberation time criteria which are dependent on room usage. As you may expect in areas where concentration and clear communication is required the criteria are stricter. For example, the criteria for reverberation time within classrooms is 0.8 Seconds TMF whereas the reverberation time criteria for a dining room where concentration and clear communication is less important is 1.0 Seconds TMF. In order to achieve the relative criteria good acoustic design should be undertaken from the outset. The use of hard reflective materials can often cause excess reverberation and thus the correct materials and surface finishes should be designed into the school or educational building. The use of carpets of sound-absorbing ceilings and wall panels can be implemented to achieve the desired learning environment fostering great communication throughout.

Sources:

BB93 Acoustic Design of Schools Performance Standards - https://www.gov.uk/government/publications/bb93-acoustic-design-of-schools-performance-standards