CPD 13 2022: Designing acoustics for learning environments

Why does it matter where we learn?

The value of education and the merits of investing in learning are undeniable. But many studies have shown that the quality of school buildings can either help or hinder learning.

Building Education, a 2002 study by Helen Clark at the Institute of Education, said: “Physical features, such as light, space, furnishings and equipment, can make people feel valued – or not. This affects their behaviour and attitudes and can significantly enhance or impede the learning process.”
Likewise, Research Report No. 242 by PwC and the Department for Education (DfE) found “evidence of a positive and statistically significant relationship between capital investment and pupil performance”.

Despite what the studies show, funding for education was in decline until very recently. This has resulted in:

• 3,731 schools being judged by surveyors as in need of immediate restoration (Guardian, 2019)
• Up to 40% of the UK school estate needing replacement or major refurbishment (National Audit Office, 2017)
• The National Education Union estimating it would take 361 years to renew the school estate based on funding levels in 2019.

The size of the school estate only compounds the large backlog of maintenance work. With around 24,000 schools in England alone, 60% of which were built before 1976 and have a design life of 60 years, simple arithmetic tells us that a significant number are approaching or have already reached the end of their design life. And the number of pupils continues to grow, particularly in secondary schools.

The Free Schools Programme, running since 2010, has driven innovation and creativity in this sector, especially in urban areas. Designs include higher-rise schools, schools within mixed-use buildings and repurposing existing buildings. In addition to this, the covid-19 pandemic has demonstrated the need for flexibility in the design and utilisation of space.

In June 2020, the UK government announced a 10-year transformative school rebuilding programme, supported by more than £1bn in funding. As well as creating inspiring learning environments for future generations, the programme is seen as an opportunity to upskill our existing workforce. A greater focus has also been placed on greener construction methods and adopting more energy-efficient practices as part of our goal to reach net zero carbon by 2050.

The DfE also stressed the importance of using modern methods of construction (MMC) to rebuild the education estate. This is a further boost to the existing £3bn Offsite School Framework, which was awarded in early 2020 and aims to “cultivate innovation and modernise the industry by increasing the adoption of MMC”. This is a once-in-a-generation opportunity for those involved in the design and construction of learning environments, to create safe, healthy and inspiring learning spaces for young people.

Learning objectives

This CPD aims to enable you to:

• Understand the importance of acoustics in schools
• Identify relevant regulations and standards
• Know the different types of sound disruptions
• Be aware of appropriate noise levels and solutions available.

The importance of acoustics in schools

Speaking and listening are critical aspects of teaching and learning. However, while modern schools often win awards for architectural design, the acoustic environment tends not to get the same level of priority.

According to the National Education Union, acoustical problems are rife. The structure of many 19th- and 20th-century schools and the open-plan design of many education settings are not conducive to learning. Open-plan designs make it almost impossible to minimise sound intrusion from other areas, and multipurpose spaces such as school halls do not cater for the full range of activities that take place within them.

Research in education settings has shown that noise and poor acoustics can:

• Lower pupils’ academic performance
• Compromise classroom control
• Damage teachers’ health
• Disadvantage children with special educational needs.

For the 3.7 million pupils and 330,000 teachers and staff in secondary schools, these conditions can have a profound impact, with many pupils struggling to clearly hear, understand and concentrate. Similarly, teachers are more likely to experience vocal problems, with women particularly at risk, as they fight to be heard in the classroom.

Nobel Prize winner Robert Koch predicted in 1910 that “one day man will have to fight noise as fiercely as cholera and pest”. He wasn’t wrong. Studies by researchers in Germany on the cardiovascular effects of environmental noise exposure found experiencing sound levels above 65dB puts individuals at an increased risk of heart attacks (according to the European Heart Journal).

Children with hearing impairments suffer the most, as hearing aids and cochlear implants fail to cut out background noise. According to the National Deaf Children’s Society, nearly half of children with limited hearing fall behind at school. The problem also disproportionately affects pupils for whom English is a second language and introverts, who prefer quieter environments.

Regulations and standards

In 2003, the DfE introduced an acoustic performance standard for new schools under Building Regulations Building Bulletin 93 (BB93).
The performance criteria laid out in BB93 provides a means of compliance with Approved Document E4 and covers all teaching and learning spaces in primary and secondary schools.

The original was deemed to be outdated and, after a lengthy consultation period, the document was republished in February 2015. Changes included the addition of school refurbishment, and in November 2015 an accompanying design guide was released to provide guidance on the best methods for achieving the required performance.

Current regulations found in the design guide focus on several factors that contribute to the overall acoustic performance of schools, including:

• Noise control, including maximum external noise levels and guidance on roofs and facades
• Internal sound insulation, including airborne and impact sound insulation, effective flanking transmission and how to meet requirements through typical wall and floor constructions
• The design of rooms for speech, music and open‑plan teaching
• Acoustic design for special educational needs.

In addition to BB93, Regulation 7 of the School Premises Regulations tells us that the acoustics and sound insulation of each room within the school must be suitable, having regard to the nature of the activities which normally take place.

In March 2015, the DfE published a document called Advice on Standards for School Premises in order to help schools understand their obligations and duties in relation to the School Premises Regulations. This document has an acoustic section that provides guidance on appropriate acoustic conditions within schools and covers sound insulation, appropriate reverberation times, indoor ambient noise levels and speech intelligibility.

Other documents for consideration include the Independent School Standards, which apply to independent schools in the same way as the School Premises Regulations. The Equality Act also places a duty on schools and local authorities to ensure accessibility plans are in place for disabled pupils and staff, which could include acoustic measures; it should be noted that very many children with hearing impairment or learning difficulties attend mainstream schools.

Here is an overview of regulation guidance across the UK and the Republic of Ireland:

• England and Wales: BB93
• Scotland: While there is no specific guidance for schools, education environments fall into acoustics for non-domestic buildings as regulated by Technical Handbook 5.1. Specifications in Scotland will often reference BB93.
• Northern Ireland: Acoustic requirements for schools are mentioned in Technical Booklet G: Resistance to the Passage of Sound, which directs users to BB93.
• Republic of Ireland: School design guide SDG 02‑05-03 Acoustic Performance in New Primary and Post Primary School Buildings was introduced in October 2020. This replaced Technical Guidance Document 021‑05. This latest guidance has many similarities to BB93 and directs the reader to BB93 for more guidance

Ambient noise levels

BB93 refers to intelligibility (background noise) levels as indoor ambient noise levels or IANL. Controlling background noise levels is vital, as high levels will affect the teacher’s ability to be heard and understood.

The World Health Organisation says noise in classrooms should not exceed 35dB. But one study of UK primary schools found the average to be 65dB (a tumble dryer is 70dB).

The main noise sources include HVAC installations, classroom equipment, traffic and aircraft noise, adjacent rooms and corridors, and this increases through the Lombard effect.

The Lombard effect can occur as a result of long reverberation times that cause speech intelligibility to be decreased and the speaker to raise their voice so they can be heard. This in turn exacerbates the situation and further increases noise levels.

Background noise is a key contributory factor to reducing the signal-to-noise ratio. To ensure speech intelligibility, the optimal sound level produced by the speaker must be greater than the background noise level.

Reverberation

Reverberation is the persistence of sound after a sound is produced, while reverberation time (RT) refers to the time required for the sound in a room to decay over a specified dynamic range, usually taken to be around 60dB, when the source is suddenly interrupted.

Long reverberation times can lead to an echoing  effect in which words overlap. Our natural inclination within a large, echoey space is to raise our voices, which then affects intelligibility. In educational settings, the target reverberation time is lower for areas where the need for clear communication is especially important.

At the opposite end of the scale, the acoustic environment can be too anechoic, usually as a result of too many absorptive finishes within the room, and this can also make it difficult to hear. Managing reverberation is essential to creating a learning environment that is fit for purpose.

Managing reverberation

To achieve adequate loudness for all listeners in a room, it is necessary that the direct sound from speaker to listener has a clear, unobstructed path. The volume of the direct sound can be enhanced by strong, short-delay reflections from room surfaces.
In classrooms and other rooms for speech, large amounts of fixed acoustic absorption are often required, particularly where rooms have high ceilings.

For classrooms, there are two main approaches:

• Make the soffit predominantly absorbent. In most cases, an acoustically absorbent suspended ceiling can provide the necessary amount of absorption. Absorbent panels on the walls and acoustically absorbent suspended rafts or baffles may also be used (the latter being particularly useful in rooms with exposed concrete soffits, providing thermal mass to optimise thermal comfort). Additional absorption may be required on the walls to meet the target criteria.
• Leave the ceiling acoustically reflective (by constructing it of, for example, plasterboard, plaster or concrete) and instead add acoustic absorption to the walls. Locating most of the absorption at a high level and some on the back wall facing the teacher will prevent a “slap echo” off the back wall. This is particularly important if the rear wall is concave or the distance from the speaker to the rear wall is greater than 8.5m. If there is insufficient space to accommodate the required amount of absorption on the walls, absorptive treatment to lighting rafts, or panels fixed directly to the soffit may be required.

Reflectors and diffusers are a particularly beneficial option in assembly halls where reflectors can be employed to direct sound and diffusers used to prevent the reflection of back walls which can otherwise be disruptive to the speaker.

Alternatively, a Rockfon solution offers the installation of a suspended ceiling grid, inlaid with acoustic ceiling tiles. The tiles are acoustically absorbent and so lower the reverberation time.

Rain noise

One source of impact noise that can affect the IANL within a room is the drumming effect created by rainfall. Rain noise can significantly increase indoor noise levels, in some instances causing them to reach as high as 70dBA.

BB93 states: “Building regulation submissions demonstrate that lightweight roofs and roof glazing have been designed to provide suitable control of reverberant rain noise.” BREEAM for Schools also provides credits for roof designs which can demonstrate that ambient noise levels are not exceeded by more than 25dB during heavy rainfall.

Sports and assembly halls that have roofs with a large surface area are particularly vulnerable to rain impact noise. The effect can be increased where the underside of the roof is exposed, with no ceiling. In the 2015 design guide, it states: “Profiled metal cladding used without mineral wool insulation or without an independent ceiling is unlikely to provide sufficient resistance to impact sound from rain on the roof.”

The performance of rooflights should also be considered in addition to the performance of the roof system. It is essential to ensure that test reports submitted by manufacturers have been carried out in accordance with BS EN ISO 140-18. It is also important to note that when reviewing rain noise calculations, the lower the sound pressure level quoted, the better the performance.

Sound insulation

Airborne noise is sound transmitted by air, while impact noise is sound transfer by vibration when an object comes into contact with a separate element. Direct transmission is noise transfer from one room to another via a shared wall, while flanking transmission is indirect noise transfer from one room to another, via a floor or wall junction.

BB93 demonstrates that sound insulation is essential for controlling noise levels between spaces, which include walls between teaching spaces, floors and circulation areas. Like water, sound energy will follow the path of least resistance. Junctions between walls, floors and partitions are all vulnerable to flanking transmission, and suitable measures should be taken to minimise this.

Table 3a (new-build) within BB93 provides guidance on the performance requirements across room types, dependent on the activity noise within the source room and the noise tolerance of the receiving room. As an example, a source room producing an average level of noise adjacent to a receiving room with a medium tolerance to noise would require 45dB of sound insulation between the two spaces.

Table 3b within BB93 provides the performance levels required through refurbishment, while table 5b provides guidance on performance levels between floors for both new-build and refurbished schools.

Sound insulation is typically expressed in terms of weighted sound reduction, or Rw. The higher the Rw, the better the performance. As impact sound is expressed as a sound pressure level (LnTw) dB, it is important to remember that the lower the dB rating, the higher the performance.

Single-leaf elements, such as a partition wall with a single layer of plasterboard on either side, can be improved by increasing the mass. Doubling the mass will increase the performance by approximately 5dB-6dB. Creating separation from the components (with an air layer, for example) and avoiding rigid connections can also help to improve the sound insulation performance.

Acoustic solutions

It is essential that the proposed site is assessed to identify existing and potential noise sources at planning and early design stages of the development. This assessment provides the essential data needed to determine the appropriate levels of sound insulation that needs to be achieved within the building envelope.

Modern methods of construction such as the use of ventilated rainscreen systems are becoming an increasingly popular option for construction schemes in educational settings. While ventilated rainscreen systems offer a number of significant benefits, determining the actual level of acoustic performance through these lightweight systems can be a challenge. Until recently, there have been few or no tested solutions that provide reliable data on sound reduction performance.

For many projects, this results in trying to determine the performance through acoustic assessments. A lack of data can lead to over-engineered systems that incorporate additional mass layers as a way to build in a safety factor.
Additional layers of mass within the system can present obstacles including additional costs (labour and materials), complex installation and increased build time.

Within the 2015 design guide, several sections recommend the use of mineral wool specifically as a means of achieving good acoustic performance. The use of mineral wool insulation designed for acoustic applications will provide good acoustic absorption and help to attenuate airborne sound transmission. Similarly, excessive noise from rain on the roof, a sound that often plagues the lightweight roofs typically found on sports halls, can be overcome by using dense mineral wool insulation in the roof build-up.

These latest guidelines also advise on the use of mineral wool insulation in the upgrading of existing suspended plasterboard ceilings and platform floors, music classrooms, recital and recording rooms, where increased low-frequency sound insulation is needed.

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