Building Bulletin 93 (BB93) Acoustic Design of Schools: Performance Standards
Building Bulletin 93 (BB93), titled Acoustic design of schools: performance standards, is a regulatory document published by the Department for Education (DfE) and the Education Funding Agency (EFA) in the United Kingdom. Originally published in February 2015, this edition supersedes Section 1 of the 2003 version of Building Bulletin 93. It establishes the minimum acoustic performance standards required to satisfy Requirement E4 of the Building Regulations 2010, the School Premises Regulations 2012, and the Independent School Standards 2013. The standards are designed to ensure that school buildings provide an environment conducive to effective teaching and learning.
The scope of this document encompasses new school buildings, extensions, and refurbishment work, including material changes of use where a non-school building is converted into an educational establishment. It applies to all teaching and learning spaces within schools, including academies, free schools, and nursery schools that are part of a primary school complex. The regulations also cover administration and ancillary spaces where their acoustic conditions affect adjacent teaching areas. Specifically, the document provides detailed performance values for Indoor Ambient Noise Levels (IANL), airborne and impact sound insulation, and mid-frequency reverberation times ($T_{mf}$).
In addition to general requirements, the document includes specific provisions for children with special hearing or communication needs, such as those on the autistic spectrum or with permanent hearing impairments. It defines standards for Alternative Performance Standards (APS) and establishes the criteria for Acoustic Commissioning to verify compliance through in-situ testing.
Regulatory Framework and Areas of Application
The acoustic conditions in schools are governed by multiple legislative frameworks. Compliance with Section 1 of this bulletin is the normal way of meeting the statutory requirements for school premises. The regulations apply differently depending on the project type and space usage:
- New Build and Extensions: Full compliance with Requirement E4 of the Building Regulations is mandatory.
- Refurbishment and Conversions: Existing buildings undergoing refurbishment should meet the standards as far as reasonably practicable to satisfy the Equality Act 2010.
- Temporary Buildings: Structures in place for more than 28 days must comply with Building Regulations, while those in place for 28 days or less are exempt from Requirement E4 but must still meet School Premises Regulations.
- Material Change of Use: Work must be carried out to ensure the building complies with the applicable requirements of Schedule 1 of the Building Regulations.
Indoor Ambient Noise Levels (IANL)
Upper limits for Indoor Ambient Noise Levels are specified in Table 1 in terms of $L_{Aeq,30mins}$ during normal teaching hours. These limits include noise from external sources and building services but exclude noise from teaching activities or equipment used within the space.
- Primary and Secondary Classrooms: New build limit is 35 dB; refurbishment limit is 40 dB.
- Open Plan Teaching Areas: New build limit is 40 dB; refurbishment limit is 45 dB.
- Music Rooms and Recording Studios: Limits range from 30 dB to 35 dB for new builds, reflecting high sensitivity to noise.
- SEN Calming Rooms: A strict limit of 35 dB applies to both new builds and refurbishments.
The document also defines tolerances for ventilation systems. For instance, the IANL can be exceeded by up to 5 dB under natural or hybrid ventilation modes in certain conditions, such as during the hottest 200 hours of the year to prevent summertime overheating.
Sound Insulation and Reverberation Standards
Performance standards for airborne sound insulation between spaces are defined by the activity noise in the source room and the noise tolerance of the receiving room. These are expressed as the standardised level difference $D_{nT,w}$.
- Airborne Sound Insulation: Between two standard classrooms, the minimum $D_{nT,w}$ is 45 dB for new builds and 40 dB for refurbishments.
- Impact Sound Insulation: The maximum weighted standardised impact sound pressure level $L'_{nT,w}$ for floors is generally 60 dB for classrooms and 55 dB for music rooms in new builds.
- Reverberation Time ($T_{mf}$): In primary school classrooms, the mid-frequency reverberation time must be $\le 0.6$ seconds for new builds. In secondary school classrooms, the limit is $\le 0.8$ seconds.
Special Educational Needs and Open Plan Learning
Students with special hearing or communication needs require enhanced acoustic conditions. BB93 mandates shorter reverberation times and higher sound insulation for these pupils to assist speech comprehension.
- SEN Teaching Spaces: The required reverberation time is $T \le 0.4$ seconds averaged from 125 Hz to 4 kHz for new builds.
- Speech Transmission Index (STI): Open plan spaces must be assessed using STI to ensure adequate speech intelligibility. A target of STI $\ge 0.6$ is required for instruction within a group.
- Speech Privacy: Between groups in open plan areas, the STI should be $\le 0.3$ to maintain privacy and reduce distraction.
Frequently Asked Questions
What is the maximum indoor ambient noise level for a new-build primary school classroom?
According to Table 1, the upper limit for indoor ambient noise level (IANL) in a primary school classroom for a new build is 35 dB LAeq,30mins.
Does Building Bulletin 93 apply to university buildings?
No, Requirement E4 and the School Premises Regulations do not cover universities or colleges of further education, though the bulletin suggests its specifications can be used as a guide for their design.
What are the acoustic requirements for temporary school buildings?
Temporary buildings in place for more than 28 days must comply with all applicable Building Regulations including Requirement E4. Those in place for 28 days or less are exempt from Building Regulation E4 but must still meet School Premises Regulations.
What is the minimum airborne sound insulation between two new-build classrooms?
Table 3a specifies a minimum standardised level difference (DnT,w) of 45 dB between two rooms with 'Average' activity noise and 'Medium' noise tolerance, such as standard classrooms.
How is reverberation time defined for students with special communication needs?
For these students, the required reverberation time is expressed as the arithmetic average of the reverberation times in the 125 Hz to 4 kHz octave bands, with a target of T ≤ 0.4 seconds for new builds.
What Speech Transmission Index (STI) value is required for open plan teaching?
Table 8 requires a Speech Transmission Index (STI) of ≥ 0.6 for instruction or critical listening activities within a group in open plan spaces.
Can Alternative Performance Standards (APS) be used in school design?
Yes, APS may be adopted for new buildings if justified by specific educational, environmental, or health and safety requirements, and must be documented and signed off by the school client body.
What is the impact sound insulation limit for a new-build music room?
Table 5 states that the maximum weighted standardised impact sound pressure level (L'nT,w) for music rooms in new builds is 55 dB.
