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11291 / 1 THE WHERRY SCHOOL – CONCEPT ACOUSTIC DESIGN PAGE 1 OF 32

THE WHERRY SCHOOL

RIBA Stage 2 Report - Acoustics

1 INTRODUCTION ......................................................................................................................... 4 1.1 BACKGROUND .............................................................................................................................. 4 1.2 INFORMATION USED IN THIS REPORT ............................................................................................ 4 1.3 INFORMATION ISSUED WITH THIS REPORT .................................................................................... 4

2 ACOUSTIC CRITERIA ............................................................................................................... 5 2.1 BUILDING REGULATIONS, APPROVED DOCUMENT E AND BB93:2015 ......................................... 5 2.2 SCHOOL PREMISES REGULATIONS AND INDEPENDENT SCHOOL STANDARDS ............................... 5 2.3 BB102 & BB104 .......................................................................................................................... 6 2.4 PRIORITY SCHOOLS BUILDING PROGRAMME ACOUSTIC STANDARDS ........................................... 6 2.5 PLANNING REQUIREMENTS ........................................................................................................... 6

3 GENERAL COMMENTS ............................................................................................................. 7 3.1 NON BB93 SPACES ...................................................................................................................... 7 3.2 DOORS LINKING TEACHING SPACES .............................................................................................. 7 3.3 LIMINAL SPACES .......................................................................................................................... 8

4 AMBIENT NOISE LEVELS ........................................................................................................ 9 4.1 GENERAL REQUIREMENTS ............................................................................................................ 9 4.2 AMBIENT NOISE CRITERIA .......................................................................................................... 10

5 NOISE SURVEYS ....................................................................................................................... 12 5.1 CLEMENT ACOUSTICS SURVEY .................................................................................................. 12 5.2 AJA SURVEY .............................................................................................................................. 12 5.3 NOISE FROM SPORTS PITCHES ..................................................................................................... 13 5.4 DISCUSSION ............................................................................................................................... 14

6 NOISE FROM PLANT AND SERVICES ................................................................................. 15 6.1 INTERNAL NOISE FROM PLANT AND SERVICES ............................................................................ 15 6.2 EXTERNAL NOISE FROM PLANT AND SERVICES ........................................................................... 16

7 SOUND INSULATION OF THE BUILDING ENVELOPE ................................................... 17 7.1 NATURAL VENTILATION / OPENABLE WINDOWS ......................................................................... 17 7.2 GLAZING .................................................................................................................................... 17 7.3 EXTERNAL WALLS AND DOORS ................................................................................................... 17 7.4 ROOF – AIRBORNE AND RAIN NOISE ............................................................................................ 17

8 SOUND INSULATION THROUGH WALLS .......................................................................... 18 8.1 AIRBORNE SOUND INSULATION .................................................................................................. 18 8.2 SOUND INSULATION BETWEEN TEACHING AND CIRCULATION SPACES ........................................ 20 8.3 SOUND INSULATION BETWEEN TEACHING SPACE WITH DOOR TO ANOTHER OCCUPIED SPACE .... 20

9 SOUND INSULATING CONSTRUCTIONS............................................................................ 21 9.1 PARTITIONS ................................................................................................................................ 21 9.2 INTERNAL GLAZING .................................................................................................................... 21 9.3 INTERNAL VENTILATORS ............................................................................................................ 22 9.4 GENERAL NOTES ON ALL WALLS ................................................................................................ 22


10 DOORS ......................................................................................................................................... 23 10.1 ACOUSTIC REQUIREMENTS FOR DOORS ...................................................................................... 23 10.2 TYPICAL DOOR TYPES ................................................................................................................. 23 10.3 GENERAL SPECIFICATION CLAUSES APPLYING TO ALL DOORS .................................................... 24

11 ROOM ACOUSTICS .................................................................................................................. 25 11.1 GENERAL PRINCIPLES ................................................................................................................. 25 11.2 CRITERIA .................................................................................................................................... 26 11.3 ACHIEVING THE CRITERIA .......................................................................................................... 26

APPENDIX A – TECHNICAL TERMS AND UNITS IN RATING NOISE .................................. 29

APPENDIX B - MEASURING EQUIPMENT AND CALIBRATION ........................................... 31

APPENDIX C - SPECIALIST ACOUSTIC MATERIALS AND SUPPLIERS ............................. 32


Adrian James Acoustics Document Control Sheet

Report prepared for: Kier Construction Eastern 1st Floor, Building 7400 Cambridge Research Park Beach Drive Waterbeach Cambridge CB25 9TN

Filename: 11291 Report 1 - Concept Design.docx

QA Control

Rev Date Author Technical Supervisor Approved by

0 25 April 2016 Joe Bear MIOA - Andy Thompson MIOA

A 26 April 2016 Joe Bear MIOA

Revision History

Rev Details

0

A Minor amendment

Disclaimer

This report was completed by Adrian James Acoustics Ltd on the basis of a defined programme of work and terms and conditions agreed with the Client. The report has been prepared with all reasonable skill, care and diligence within the terms of the Contract with the Client and taking into account the project objectives, the agreed scope of works, prevailing site conditions and the degree of manpower and resources allocated to the project. Recommendations in this report are for acoustics purposes only, and it is the responsibility of the Project Manager or Architect to ensure that all other requirements are met including (but not limited to) structure, fire and Building Controls.

Adrian James Acoustics Ltd accepts no responsibility, following the issue of the report, for any matters arising outside the agreed scope of the works.

Any surveys were conducted and this report has been prepared for the private and confidential use of our client (Kier Construction) only and cannot be reproduced in whole or in part or relied upon by any third party for any use whatsoever without the express written authorisation of Adrian James Acoustics Ltd. If any third party whatsoever comes into possession of this report, they rely on it at their own risk and Adrian James Acoustics Ltd accepts no duty or responsibility (including in negligence) to any such third party.

Unless specifically assigned or transferred within the terms of the agreement, Adrian James Acoustics Ltd retains all copyright and other intellectual property rights, on and over the report and its contents.

© Adrian James Acoustics Ltd. 2016


1 INTRODUCTION

1.1 Background

We have been appointed by Kier Construction to provide acoustic input to the design and construction of The Wherry School, a specialist school for children and young people aged four to nineteen years who have autistic spectrum disorders. The school will be located on part of the Hewitt Academy site in Norwich.

The aims of this report are to set out the acoustic requirements for the scheme and to provide guidance on practical means of achieving the required acoustic conditions. It includes a discussion of the acoustic requirements for each type of room along with accompanying acoustic criteria plans summarising these requirements.

It is not necessary to be familiar with the technical aspects of acoustic design to understand our conclusions and recommendations. Because of the technical nature of acoustic design, however, this document contains a number of specialised terms which are explained in the Appendices.

1.2 Information used in this report

This report is based on information provided by Kier Construction and the following drawing by LSI Architects:

Drawing No Revision Title

16011-2000 P7 General Arrangement

16011-1730 P6 Site Plan Proposed

1.3 Information issued with this report

This report should be read in conjunction with the following acoustic criteria plan.

Drawing No Revision Title

11291 ACP_01 0 Acoustic criteria plan


2 ACOUSTIC CRITERIA

2.1 Building Regulations, Approved Document E and BB93:2015

Requirement E4 from Part E of Schedule 1 to The Building Regulations 2000 (as amended 2003) states that:

“Each room or other space in a school building shall be designed and constructed in such a way that it has the acoustic conditions and the insulation against disturbance by noise appropriate to its intended use.”

Approved Document E in support of the Building Regulations states that:

“In the Secretary of State’s view the normal way of satisfying Requirement E4 will be to meet the values for sound insulation, reverberation time and internal ambient noise which are given in Section 1 of Building Bulletin 93”.

The Building Regulations apply to new schools and extensions to existing schools, so any school buildings built since 2003 should comply with the acoustic standards in BB93. This also applies to any spaces refurbished or subject to change of use so as to require compliance with Building Regulations.

BB93:2015 sets out mandatory acoustic standards for compliance with Building Regulations in new schools as well as the separate duties of the School Client Body under the School Premises Regulations, the Independent School Standards and the Equality Act. Even where Building Regulations are not applicable, the School Premises Regulations (SPRs) and Independent School Standards invoke similar acoustic standards.

BB93:2015 sets out more stringent criteria children with special hearing and communication needs including, but not being limited to:

Permanent hearing impairment

Speech, language and communication difficulties

Visual impairments

Fluctuating hearing impairments caused by conductive hearing loss

Attention deficit hyperactivity disorders (ADHD)

An auditory processing disorder or difficulty

Being on the autistic spectrum

Given that the Wherry School will provide specialist, non-mainstream teaching accommodation for children with autistic spectrum disorders it is clear that the more stringent criteria for students with special hearing or communication needs are triggered in this case.

2.2 School Premises Regulations and Independent School Standards

The School Premises Regulations (SPRs) and Independent School Standards (ISSs) apply to both new and existing school buildings, including the refurbishment of existing teaching and learning spaces. The School Client Body is responsible for ensuring compliance with the Regulations. The School Client Body consists of both the Commissioning Authority (which can be central government, a local authority or the School itself) and the School Entity, which is the entity having day-to-day control of the School and may be represented by the Head teacher or Governors.


Both the SPRs and ISSs contain a similar statement to that in Requirement E4 of the Building Regulations:

“The acoustic conditions and sound insulation of each room or other space must be suitable, having regard to the nature of the activities which normally take place therein.”

Both sets of regulations include clarifications of what is meant by the term “suitable” and what is meant by “special requirements”:

“Any requirement that anything provided under these Regulations must be “suitable” means that it must be suitable for the pupils in respect of whom it is provided, having regard to their ages, numbers and sex and any special requirements they may have.” “A pupil has “special requirements” if the pupil has any needs arising from physical, medical, sensory, learning, emotional or behavioural difficulties which require provision which is additional to or different from that generally required by children of the same age in schools other than special schools.”

In addition to the design and construction standards covered by the Building Regulations, the School Premises Regulations and Independent School Standards cover the performance in use of schools. This means that operational noise levels (including noise from equipment such as whiteboard projectors and computers) in teaching and learning spaces must be suitable for the activities taking place.

2.3 BB102 & BB104

Building Bulletin 102 “Designing for disabled children and children with special educational needs” provides some qualitative outline advice for the acoustics of spaces with different special educational needs. However, it does not set any specific acoustic criteria, instead referring back to the numerical criteria set out in Building Bulletin 93 “Acoustic Design of Schools”. BB102 was recently superseded by Building Bulletin 104 “Area guidelines for SEND and alternative provision” which sets out the floor area requirements for SEND schools but does not contain any guidance on acoustics or noise.

2.4 Priority Schools Building Programme acoustic standards

We understand that the contract documentation for the project requires the scheme to meet the acoustic criteria set out in ‘The Acoustic Performance Standards for the Priority Schools Building Programme v1.7 May 2013. That document was issued by the Education Funding Agency before the current version of BB93 was published in 2015. However, the PSBP document was based on a draft of the revised version of BB93 standards and the acoustic criteria set out in the two documents are the same.

2.5 Planning requirements

We understand that the Environmental Health Officer has reviewed the scheme and confirmed that a formal impact assessment of noise from the proposed site will not be required given the relatively large distances to the nearest dwellings and the existing noise climate in the area.


3 GENERAL COMMENTS

3.1 BB93 Classification

There are a number of spaces in the scheme that do not have specific criteria set out for them in BB93. There are also a number of spaces where we consider that the criteria set out in BB93 for mainstream teaching are not appropriate in this case. These spaces are listed below along with our recommended criteria.

Ambient noise criterion, dB LAeq,30mins

Noise tolerance

Activity noise level

Reverberation time (Tmf), seconds

Learning Resource Centre (LRC)

[1]

Life Skills [2]

Science

Food Tech

Art / Design / Tech

Sixth form study

30 Average Low

Tmf ≤ 0.4 averaged from 125Hz to 4kHz octave band centre

frequencies and

Tmf ≤ 0.6 in every octave band in this

range

Sensory Room 30 Average Low ≤ 0.6

Soft therapy 40 High Medium ≤ 0.6

Sixth Form Social 40 Average Medium ≤ 0.8

Hall [3]

30 High Low 0.8 - 1.2

Table 1 – Recommended criteria for non BB93 spaces

[1] We understand that the Learning Resource Centre will be used for teaching and study and have therefore applied the same criteria as for classrooms.

[2] We understand that the Life Skills room will be a classroom used for teaching students practical domestic skills and have therefore applied the same criteria as for classrooms.

[3] We recommend that the lower ambient noise criterion for teaching spaces intended specifically for students with special hearing or communication needs is applied to the Hall. However, applying the more onerous reverberation time criteria to this space would be impractical because the large volume would require unfeasibly large areas of absorption.

3.2 Doors linking teaching spaces

The following pairs of rooms have a door linking them directly to one another.

Dining hall and Food Tech Room

Classrooms and Individual Rooms

Sixth Study and Sixth Form Social

This arrangement is not permitted under BB93 except where there is clear operational requirement for the spaces to be linked. Where it is essential to link a teaching space with another occupied room via an interconnecting door for operational or safety purposes, BB93 requires that a doorset should be used with a rating of at least 35 dB Rw. The surrounding wall (including any glazing) should have a composite sound insulation rating of at least 45 dB Rw.


Despite requirement for higher performance door sets, the arrangement will limit the standard of sound insulation achievable between the two spaces. It is important that the client understands that this may limit the options for the simultaneous uses of these two spaces.

3.3 Liminal spaces

The client brief identifies the need for number of break-out “liminal” spaces in the corridors outside classrooms. We understand that the intention is for these spaces to give students space to transition between the varied sensory environments in different areas of the school. It is important to note that the liminal areas have not been designed for formal teaching activity, and despite the high-rated sound-insulating doors to the classrooms, any noisy activity in the liminal spaces has the potential to disturb teaching of quiet activities in the surrounding classrooms. It will therefore be necessary to carefully manage these spaces.


4 AMBIENT NOISE LEVELS

4.1 General requirements

BB93 sets criteria for acceptable indoor ambient noise levels (IANL) inside different types of room. The indoor ambient noise level includes noise contributions from:

External sources outside the school premises (including, but not limited to, noise from road, rail and air traffic, industrial and commercial premises).

Building services (e.g., ventilation systems, plant, drainage, etc). If a room is naturally ventilated, the IANL is calculated and measured with ventilators or windows open as required to provide adequate ventilation (as described in Section 1.1.3 of BB93). If a room is mechanically ventilated or cooled, the plant should be assumed to be running at its normal operating duty.

Window actuator and damper noise.

The indoor ambient noise level excludes noise contributions from:

Teaching activities within the school premises, including noise from staff, pupils and equipment within the building or in the playground. Noise transmitted from adjacent spaces is addressed by the airborne and impact sound insulation requirement.

Equipment used in the space, (e.g. machine tools, CadCam machines, dust and fume extract equipment, compressors, computers, projectors, fume cupboards) as these sources are considered as operational noise. However, these noise sources should be considered in the design process.

Rain noise. However, Building Regulation submissions should demonstrate that lightweight roofs and roof glazing have been designed to provide suitable control of rain noise reverberant sound pressure level in a space (calculated using laboratory test data with ‘heavy’ rain noise excitation as defined in BS EN ISO 140-18). Levels during heavy rain should not be more than 25dB above the appropriate indoor ambient noise level (for refurbishments, this applies only to new roofing elements and not to repairs on existing roofs).


4.2 Ambient noise criteria

BB93 sets out noise levels in terms of the highest LAeq, 30 minutes expected to occur during school hours. The relevant criteria for this project are as follows:

Room / area type Upper limit for indoor ambient noise level

(dB LAeq, 30 min)

Teaching space intended specifically for students with special hearing or communication needs (all classrooms and associated individual rooms).

Music / Drama

LRC

Science

Food Tech

Art / Design / Tech

Life Skills

Sixth Form Study

Sensory Rooms

Hall

30

SEN Calming rooms

35

Interview and counselling rooms

Soft therapy

Sixth form social

Staff rooms, offices and meeting rooms

Sick bay

Parents’ Room

40

Dining room 45

Kitchen

WCs 50

Table 2 - Ambient noise limits


The criteria listed in Table 2 should apply to all plant and building services under “normal” conditions. BB93 provides relatively lengthy and complex definitions of “normal” conditions in terms of average carbon dioxide concentration. The definitions are different for natural hybrid and mechanical ventilation modes and are not reproduced in this report. An increase of 5 dB over these levels is permitted under the following conditions:

When mechanical ventilation plant is being used to prevent summertime overheating during the hottest 200 hours of the year, or to provide intermittent boost ventilation, for the dilution of fumes in during practical activities in spaces used for science, art, food technology and design and technology. In any case this increase is only permitted if the ventilation system is under local control of the teacher, e.g. with a switch in the classroom.

When natural ventilation or a hybrid mechanical / natural ventilation system is used to provide normal ventilation for teaching and learning activities

An increase to allow an internal ambient noise level of up to 55 dB LAeq is permitted under the following conditions:

When a natural or hybrid ventilation system is being used to prevent summertime overheating during the hottest 200 hours of the year,

When a natural ventilation system with no mechanical component is used to provide intermittent boost ventilation, for the dilution of fumes in during practical activities in spaces used for science, art, food technology and design and technology. In any case this increase is only permitted if the ventilation system is under local control of the teacher, e.g. by opening windows or vents either manually or using a switch in the classroom.


5 NOISE SURVEYS

5.1 Clement Acoustics Survey

Clement Acoustics Ltd was commissioned by Mace Group to measure existing ambient noise levels at the site. This noise survey report concludes that

However, the noise survey, calculations and assessment methodologies used by Clement Acoustics contain a number of very serious technical flaws and we therefore consider that the conclusions made in their report should be disregarded.

5.2 AJA survey

5.2.1 Site description and survey methodology

We visited the Hewitt Academy on 8 March 2016 and measured noise levels across the site of the proposed building. The site is on the south-eastern corner of the Hewitt Academy campus. It is bounded by the Hewitt science building and swimming pool to the North, Hall Road to the East, “Goals” five-a-side football centre to the South and the Hewitt Academy playing fields to the West. The A146 Lakenham Road runs east to west, approximately 150m south of the site of the proposed building.

Figure 1 - Measurement positions. Imagery and map data ©Google 2016

A

C

D B

E

Proposed building


We measured noise levels at various positions around the site, which corresponded with the approximate location of the facade of the proposed building as shown in Figure 1. Our measurements complied with the guidelines set out in BB93 and were taken in free field conditions with the microphone at a height of approximately 1.2m above the ground. The parameters measured included octave band and A-weighted Leq,5 min.

The main sources of ambient noise during the survey were local traffic on Hall Road, continuous distant traffic on the A146 Lakenham Road and other roads, activity on the light industrial estate to the south-east of the site and high-altitude aircraft. Note that there was no activity on the sports courts and pitches to the south and west of the Wherry School site at the time of the survey. Noise from these sources is discussed separately in Section 5.3 of this report.

We measured noise levels for 10 to 25 minutes at each position. Given the constant nature of the various noise sources we judged this to be representative of the BB93 30-minute assessment period at each location.

5.2.2 Results

The results are summarised in Table 3 along with the calculated internal ambient noise levels in the building with windows open.

Measurement location

Measured external noise level,

LAeq,30mins, dB

Calculated internal ambient noise level,

LAeq,30mins, dB

A 60.7 43.3

B 54.8 38.0

C 55.1 39.0

D 54.8 38.6

E 51.3 35.6

Table 3 - Noise levels measured around the proposed site

5.3 Noise from sports pitches

There was no activity on the Goals site or the Hewitt playing fields during our measurements. However, we understand that the Goals and Hewitt Academy pitches are used regularly during school hours and we would expect the activity from these pitches to be a significant source of external noise on the Wherry School site.

The pitches are outside the school premises and, more importantly, will be outside the management control of the Wherry School. Noise from the adjoining sports courts and pitches should be considered as a contributory factor when considering the internal ambient noise levels within the proposed building.

Without a direct line of communication with Goals and the Hewitt Academy it has not been possible for us to arrange a repeat survey to measure noise levels when the pitches are in use. We intend to return to the site for this additional survey as external sporting activity increases over the course of the summer term.

As a rough guide, our previous measurements of noise from sports pitches suggests that noise levels are typically around 60-65 dBA LAeq,30mins at a distance of 10m from the edge of the pitch. The levels of noise on the Wherry School site from the


surrounding sports pitches will be dependent on how many pitches are in use at any one time and the type of activity.

We estimate that, if only the two large football courts closest to the Wherry school site were in use, this would generate a level of around 60 dB LAeq,30min at the facade of the proposed building.

5.4 Discussion

The calculated internal ambient noise levels all exceed the 35 dB LAeq,30min criterion for internal ambient noise levels (including a 5 dB(A) relaxation for naturally ventilated spaces) at all locations. At the time of our survey, the noisiest parts of the site were the areas close to the eastern boundary and at all locations except Location E, the measured noise levels were substantially (3 dB or more) above those at which we would expect natural ventilation to be a viable option.

At location E, in the absence of noise from the sports pitches, the measured noise levels were less than 1 dBA above that at which we would expect natural ventilation to be viable. However, we understand that the various sports courts and pitches to the south-west of the Wherry School site are expected to be used extensively during the school day. This means that the noise levels reported in Table 3 are likely to underestimate of the true noise levels at the site. On that basis we recommend that all teaching rooms are mechanically ventilated to control noise break-in to the building. The only exception to the spaces overlooking the central courtyard where windows will be screened the various noise sources outside the site.

The spaces requiring mechanical ventilation for acoustic reasons are as follows:

01 Standard Classroom (EY, KS1 & KS2) and 01b Individual room

03 Standard Classroom (EY, KS1 & KS2) and 03b Individual room

19 Life Skills

20 Standard Classroom (Post 16) and 20 b Individual (Post 16)

21 Standard Classroom (Post 16) and 21 b Individual (Post 16)

22 Sixth Form Study

56 LRC

57 Science

58 Art/Design/Tech

60 Standard Classroom (KS3 & KS4) and 60b Individual room









6 NOISE FROM PLANT AND SERVICES

6.1 Internal noise from plant and services

Noise from plant and services should not cause the ambient noise levels to exceed the criteria set out in Table 4. This includes break-in noise from items of external plant. The dBA levels translate approximately to NR-based noise limits as follows:

Permitted ambient noise upper limit Equivalent PNC / NR criterion

30 dB LAeq,T NR25

35 dB LAeq,T NR30

40 dB LAeq,T NR35

45 dB LAeq,T NR40

50 dB LAeq,T NR45

Table 4 – Approximate PNC or NR limits to comply with ambient noise criteria

Where mechanical ventilation and plant is to be used, the M&E contractor should ensure that noise from the mechanical ventilation system does not exceed the ambient noise criteria or restrict the performance of sound insulating constructions.

In this case the mechanical ventilation for each space is proposed to be provided by local MVHR units mounted in the ceiling void of the space they serve. Compliance with criteria for internal ambient noise levels is the responsibility of the mechanical services designers and installers. However, a calculation check on noise levels for the proposed units suggests that additional noise control measures will be required to meet the internal ambient noise criteria for teaching spaces.

We therefore recommend that rooms with mechanical ventilation units mounted in the ceiling voids are fitted with a suspended ceiling system that incorporates sound insulation and sound absorption, such as Combison Duo by Ecophon. It is important to note that the ceiling system will also need to meet the sound absorption requirements set out in Section 11 of this report. Alternatively, separate sound insulating tiles could be installed on top of a conventional grid tile ceiling.

There are a number of noise issues to be considered in the design of mechanical ventilation, including:

Fan noise and other duct-borne noise in teaching rooms.

Aerodynamic noise, e.g. from high speed airflows at diffusers and in ducts.

Noise from ventilator actuators and dampers – there are special requirements for these and we can assess specific systems against these requirements if required.

Cross-talk through ducts between rooms: cross-talk attenuators may be required.

Airborne and structure-borne noise transmission from plant rooms to adjoining teaching rooms. In particular, plant may require efficient vibration isolation and possibly inertia blocks.

Noise emissions to the atmosphere from plant room louvres.


Noise from services should be steady and broadband in nature with no recognisable tones or characteristics such as ‘hums’, ‘clicks’ or ‘buzzes’. This is particularly important for schools with SEN provision because children with some special needs can be very sensitive to tonal and intermittent noises.

6.2 External noise from plant and services

We understand that the council’s Environmental Health Officer has reviewed the scheme and confirmed that a formal impact assessment of noise from the proposed site will not be required given the distances to the nearest dwellings and the existing noise climate in the area.

The noise limits from external plant and services will therefore be governed by the limits on noise break-in set out in the internal ambient noise criteria for the surrounding teaching spaces. It will be responsibility of the designers and installers of M&E equipment to ensure that noise from plant and services does not exceed the figures in Table 2 of this report.

The precise level difference across open windows is dependent on the spectrum of the external noise and the opening arrangement of the windows. Noise break-in through open windows typically results in an approximate difference of 15 dB(A) between external and internal noise levels. Therefore, to meet the internal ambient noise levels the noise from external plant and services should not exceed 45 dB LAeq,T outside the naturally ventilated classrooms in the central courtyard and 50 dB LAeq,T outside Hewitt School classrooms. These figures are equivalent free field levels and do not include the effect of facade reflections.


7 SOUND INSULATION OF THE BUILDING ENVELOPE

7.1 Natural ventilation / openable windows

As discussed in Section 5 of this report, the ambient noise levels are relatively high at the proposed site and the majority of teaching rooms will require mechanical ventilation.

7.2 Glazing

Although the noise levels are relatively high at the site, there will be no special acoustic requirement for external windows, and conventional double glazing with a minimum sound insulation rating of 30 dB Rw will be adequate.

7.3 External walls and doors

The facades of the building should achieve a minimum sound insulation performance of 40 dB Rw. We would expect all conventional facade constructions to achieve this performance as a matter of course.

External doors on the outer facades of the building should achieve a minimum sound insulation performance of 30 dB Rw.

7.4 Roof – airborne and rain noise

Note: It is important to note that airborne sound insulation and rain noise are separate quantifiers which are measured, rated and specified differently. Many manufacturers quote airborne sound insulation data but not rain noise test data.

We understand that the roof is to be a lightweight construction consisting of a bitumous felt roof on rigid thermal insulation on a profiled metal deck with a suspended grid ceiling below. We would expect this type of construction to provide a sufficient standard of airborne sound insulation. However, sound insulating ceiling tiles would be required to meet the rain noise requirements in teaching areas. We therefore recommend that the combination ceiling tiles specified in mechanically ventilated teaching rooms are also installed in the naturally ventilated classrooms and individual rooms.

Alternatively the overall roof build-up could be upgraded (e.g. with an anti-drumming membrane) to meet the rain noise criterion in all areas.


8 SOUND INSULATION THROUGH WALLS

8.1 Airborne sound insulation

BB93 addresses this for teaching spaces by specifying the weighted standardised Level Difference, DnT,w. This is the standardised level difference in accordance with BS EN ISO 16283-1 weighted in accordance with BS EN ISO 717-1. The reference reverberation time, T, is either:

The upper limit for the mid-frequency reverberation time, Tmf,max for the receiving room type set out in Table 6 of BB93, as discussed later in this report ;

Or, for commissioning measurements:

The measured reverberation time in each third octave band, provided that the mid-frequency reverberation time, Tmf, complies with the requirements in Table 6 of BB93.

DnT,w is the sound insulation achieved between rooms as built, including the effects of workmanship and flanking transmission through the surrounding structure. This quantity is used because it can be measured on site.

The intrinsic sound insulation of a given material is quoted in terms of the Weighted Sound Reduction Index, Rw. This is a quantity measured in a laboratory, normalised for the area of the partition and the acoustics of the laboratory, and so is affected only by the material under test.

The DnT,w achieved on site can be calculated from the Rw of the material used, the area of the separating element, and on the volume and reverberation time of the receiving room. An allowance also has to be made for workmanship and flanking transmission.


We have calculated the Rw required in each case to achieve the DnT,w required by BB93.

Source room Receiver Room DnT,w

criterion Recommended

Rw (min)

Kitchen Hall 55 60

Music/Drama MI Room 55 60

Music/Drama Soft Therapy 55 60

Music/Drama Calming Room 55 60

Calming room Soft Therapy 55 60

Calming room SEN classroom 55 60

Music/Drama Hall 55 60

SEN classroom SEN classroom 50 55

Life skills Post 16 Classroom 50 55

Plant room [1]

Sixth Form Social

50 55

Sensory Room SEN classroom 50 55

WCs SEN classroom 50 55

WCs Sensory Classroom 50 55

Soft Therapy MI Room 50 55

Meeting room/interview room SEN classroom 45 50

Repro LRC 45 50

Life Skills Psych Therapy 45 50

Meeting room/interview room Sensory Room 45 50

Table 5 - Airborne sound insulation requirements between rooms

Notes

[1] The standard of sound insulation required will depend on plant noise levels in the plant room, but typically should be no lower than the criterion listed here. We can comment further as the schedule of plant and services is developed.


8.2 Sound insulation between teaching and circulation spaces

Because of the shapes and volumes of most corridors, it is impossible to measure the DnT,w between corridors and rooms in a reproducible way. BB93 therefore specifies sound insulation criteria between these spaces in terms of types of construction, and therefore Rw only. This also applies to doorsets, glazing and ventilators between these areas. BB93 specifies the following performance standards for airborne sound insulation between circulation spaces and spaces used by students.

Type of space used by students

Minimum Rw dB

Composite Rw of wall and

glazing with no ventilator

Composite Rw of wall, glazing and ventilators

Doorset

Teaching space intended specifically for use by students with special hearing or communication needs

45 38 35

All other rooms used for teaching or learning

40 33 30

Table 6 - Airborne sound insulation requirements between corridors and rooms used by students

8.3 Sound insulation between teaching space with door to another occupied space

Where it is essential to link a teaching space with another occupied room via an interconnecting door for operational or safety purposes, BB93 requires that a doorset should be used with a rating of at least 35 dB Rw. The surrounding wall (including any glazing) should have a composite sound insulation rating of at least 45 dB Rw.


9 SOUND INSULATING CONSTRUCTIONS

We have calculated the Rw (laboratory sound insulation rating) required to achieve the on-site BB93 performance criteria. These are shown on the acoustic criteria plan that accompanies this report.

9.1 Partitions

We understand that the walls are proposed to be constructed from metal studwork lined on both sides with one layer of 15mm DuraLine board and one layer of 12.5mm SoundBloc. In some cases there will be a requirement to provide ply pattressing for fixtures and fitting.

The following wall specifications will meet the various performance standards:

40 dB Rw - Minimum 48 mm metal studwork, no mineral wool required. 12.5mm ply can be used instead of 12.5mm SoundBloc if required.

45 dB Rw - Minimum 48 mm metal studwork, no mineral wool required. 12.5mm ply can be used instead of 12.5mm SoundBloc if required provided 25mm mineral wool (e.g. Isover Apr 1200) is included in the cavity to achieve the required sound insulation performance.

50 dB Rw - Minimum 48 mm metal studwork with 25mm mineral wool (e.g. Isover Apr 1200) between studs. If 12.5mm ply is used instead of 12.5mm SoundBloc the studwork should be at least 70mm deep and 50 mm mineral wool (e.g. Isover Apr 1200) will be required between the studs.

55 dB Rw - Minimum 70 mm AcouStuds (or other equal and approved proprietary resilient studwork system) with 25mm mineral wool (e.g. Isowool Apr 1200) between studs. If 12.5mm ply pattressing is required this should be installed in addition to the 12.5mm SoundBloc in walls rated at 55 dB Rw.

60 dB Rw – Twin studwork frames constructed from 50mm I stud frameworks with a minimum 150mm cavity between the inner faces of the board and 50mm mineral wool (e.g. Isover Apr 1200) between studs. 12.5mm ply can be used instead of 12.5mm SoundBloc if required.

9.2 Internal glazing

The required sound insulation performance for internal glazed screens within partitions is governed by the size of the screen and the area and construction of the surrounding wall. We will determine the minimum performance requirements for individual screens as the design is developed.


9.3 Internal ventilators

To meet the sound insulation requirements set out in Table 6BB93 suggests that internal ventilators to circulation areas should meet the following requirements:

To SEN teaching rooms : Dne,w – 10logN ≥ 37 dB

To other rooms occupied by students : Dne,w – 10logN ≥ 32 dB

Where Dne,w is the element normalised performance requirement for ventilators and N is the number of ventilators serving a given space. The required insertion losses to achieve these performance requirements depend on the number of ventilators and the size of the ventilation openings to each room which has not eben determined yet.

9.4 General notes on all walls

9.4.1 Dry Lining

We do not recommend any separating construction using only one layer of board on either side of studwork, even where such a construction might comply with the required Rw. However, if such constructions are used, we recommend that great care is taken to ensure that these partitions are constructed with no gaps or weaknesses in the plasterboard as these types are partition are more susceptible to damage and reduced sound insulation performance.

All joins must be staggered, taped and sealed, with any gaps at the perimeter sealed in all thicknesses of plasterboard using dense flexible sealant. All constructions should be built in accordance with detailing for sound insulating partitions in the British Gypsum White book, or equivalents by Lafarge or Knauf.

9.4.2 Extent of walls

All sound insulating partition walls should be built from structural slab to soffit. Walls should not be built off screeds laid on thermal insulation.

We do not normally recommend terminating partitions or walls at, or just above the soffit of a suspended ceiling as this demands a ceiling performance in respect of both fire resistance and sound insulation which is difficult to achieve and maintain in practice in school buildings, particularly where ceilings are penetrated for lighting and services. This is particularly relevant for lightweight acoustically absorbent ceilings, which provide very little sound insulation.

9.4.3 Deflection heads

Deflection heads, if required, should be built in accordance with the dry lining system manufacturer’s instructions for optimum sound insulation. Specialist trapezoidal filler pieces will be required to close the gaps between profiles in the metal roof deck.

9.4.4 Service penetrations

Penetrations through sound insulating walls for services require acoustic detailing and we can advise on these individually if required.


10 DOORS

10.1 Acoustic requirements for doors

Doors are generally the weakest part of any partition wall, and as with internal glazing, the sound insulation criteria for partitions between rooms apply to the whole partition including the door.

In general a lightweight hollow-core door will only provide about 15 dB Rw and a good quality, 45 mm solid door with compressible seals will achieve up to 30 dB Rw. Special acoustic doors can achieve higher ratings, but they are generally costly, too heavy to use as classroom doors, and the sealing arrangements (which will require threshold seals) are too complex for general use in schools.

A single 30 dB Rw door in a 52 dB Rw partition between two classrooms typically reduces the overall Rw of the combined wall and door to 41 dB. The overall DnT,w achieved on site would then be about 38 dB. For this reason it is not normally permissible to have doors leading directly between classrooms.

10.2 Typical door types

We have identified door types in the Acoustic Criteria Plans included with this report. The following door types are referred to:

10.2.1 Doors without marked-up criteria

These have no acoustic requirement. Typically these are doors to WCs, stores, fire doors in corridors and some external doors. These may be hollow-core doors and do not require acoustic seals. Note, however, that it is still necessary to prevent noise from these doors slamming affecting adjacent areas. To prevent slamming these should be fitted with door-closers as specified for other door types. However, previous experience has identified that door closers can give rise to behavioural problems in ASD schools and we recommend that this is referred to the client.

10.2.2 Rw30 doors

These are primarily for use between general teaching spaces and corridors. The contractor should provide test certificates from an independent accredited acoustic test laboratory to demonstrate that the doors, seals and frames achieve Rw 30 when tested in accordance with BSEN ISO 140/3. This rating applies to both single and double-leaf doors.

Typically, if in wood, Rw30 doors will be close-fitting, solid-core doors at least 45 mm thick, or 4 mm plywood faced laminated solid core construction with no gaps or hollows in the core, and with 8 mm hardwood edging. Vision panels, if fitted, should consist of glass at least 8 mm thick and should be sealed into the door using non-hardening mastic under a hardwood bead to create an air-tight join between glass and wood. Doors should be close-fitting and fitted with efficient compressible seals at the head and jamb, installed and adjusted in accordance with the manufacturer’s recommendation so as to be compressed when the doors are closed. Doors must not be undercut or fitted with transfer grilles.

Double doors should be fitted with compressible seals at the meeting stile or with efficient rubber or neoprene wipe seals at the central vertical join, which shall be radiussed and shaped to ensure a smooth and continuous seal when closed.


10.2.3 Rw35 doors

These are higher-performance internal door sets with a minimum sound insulation rating of Rw35. The contractor must provide test certificates from an independent accredited acoustic test laboratory to demonstrate that the doors, seals and frames achieve Rw35 when tested in accordance with BSEN ISO 140: Part 3.

10.3 General specification clauses applying to all doors

Installation – All doors, frames, seals and other components should be installed in accordance with the manufacturer’s recommendations for optimum acoustic performance, with particular reference to the gap sizes for efficient operation of each type of seal. When closed there should be no gaps between seals at perimeters, thresholds and meeting stiles.

Ease of opening - Attention is drawn to the need for compliance with Building Regulations Part B (Fire safety) and Part M (Access to and use of buildings). There may be a conflict between the acoustic and ease of access requirements for some types of acoustic doors. No definitive guidance is currently available on this, although many Building Control Officers allow a relaxation of the 20N requirement in Part M.

Door closers – Although not a formal requirement under BB93, to prevent noise from doors slamming we recommend that efficient door closers should be fitted and adjusted in accordance with manufacturer’s recommendations to prevent doors from slamming. The use of soft or compressible seals at door frames can also help to reduce noise from doors closing.

Finger guards – Finger protection devices do not generally have any effect on acoustic performance but may be required for safety purposes, and should be considered by the Architect, Client or appropriate adviser.


11 ROOM ACOUSTICS

11.1 General principles

BB93 sets out criteria for the room acoustics of teaching areas in terms of Reverberation Time (RT). This is defined as the time taken for the sound pressure level in the space to decrease by 60 dB. Subjectively, a long reverberation time gives a “live” acoustic while rooms with short reverberation times are “dry” or “dead”. The most common acoustic problems in schools are over-reverberant rooms (i.e. those with long reverberation times) which give rise to poor speech intelligibility and, in some rooms, high reverberant noise levels. In general BB93 addresses this by setting the maximum acceptable RT in each type of room, although in music rooms and assembly halls, a range of RTs is defined.

The reverberation time of a room depends on its volume (large rooms naturally tend to have longer RTs than smaller ones) and on the acoustic absorption of the room finishes and contents. The acoustic absorption of a material is defined by a coefficient between 0 (totally reflective) and 1 (totally absorbent) at each frequency. Acoustic absorption and RT vary as a function of frequency. At low (bass) frequencies, most materials are less absorptive than at medium and high (treble) frequencies, so in most rooms the RT is longest at low frequencies. It is usual to define the RT at each octave from 63 Hz (two octaves below middle C) to 4 kHz (four octaves above). For convenience, the RT is often expressed as a single figure referring to the value at 500 Hz (“mid-frequency”) but values at other frequencies must be correct in relation to this.

For ease of reference, the standard EN ISO 11654 classifies acoustically absorbent materials according to their minimum acoustic absorption, with Class A material being the most absorbent and Class E providing relatively little absorption.

In general, the area of acoustic absorption required in a typical classroom will be of the same order as the floor area. Therefore, the easiest way of achieving the appropriate RT will be by installing an acoustically absorbent ceiling.


11.2 Criteria

BB93 defines acceptable RTs in terms of the mid-frequency reverberation time, Tmf, which is the average of the values at 500, 1000 and 2000 Hz for unoccupied and unfurnished rooms. For this project the relevant values are as follows:

Room / area type Tmf, seconds

Teaching space intended specifically for students with special hearing or communication needs (All classrooms and associated individual rooms).

Music / Drama

Science

Food Tech

Art / Design / Tech

Life Skills

Sixth Form Study

Sensory Rooms

SEN Calming Rooms

Soft Therapy

LRC

Tmf ≤ 0.4 averaged from 125Hz to 4kHz octave band centre

frequencies and

Tmf ≤ 0.6 in every octave band in this

range

Meeting / Interview rooms (SEN Base, Psych Therapy, MI Room, Student Counselling, Visiting Prof,)

Sixth form social

≤0.8 seconds

Multipurpose hall 0.8 – 1.2 seconds

Music / Drama

Dining Room

Staff Room and offices

1.0 seconds

Administration and ancillary spaces:

Corridor, stairwell

Toilet

[1]

≤ 1.5

Table 7 - Reverberation time criteria

Note

[1] See Section 1.7 of BB93 regarding corridors and stairwells, and Section Error! Reference source not found. of this report.

11.3 Achieving the criteria

With the exception of the hall, grid tile ceilings are proposed throughout the school.


11.3.1 Teaching rooms

Teaching rooms will generally require Class A ceilings to meet the very low reverberation time requirement for SEN Teaching space intended specifically for students with special hearing or communication needs (All classrooms and associated individual rooms). Note that specialist combination sound insulating and absorbing tiles will be required to meet the rain noise and plant noise requirements.

11.3.2 Hall

We understand that the ceiling in the hall will be perforated plasterboard to provide an impact resistant finish. We recommend that the ceiling product achieves Class C absorption (e.g. Quattro 41 by British Gypsum). An additional area of approximately 20m2 of acoustically absorbent wall panels evenly spaced around the available wall area will be required to control low level reflections between the walls of the hall. Some suitable impact resistant wall panel products are listed in Appendix C of this report.

11.3.3 Dining room, corridors, interview rooms, staff areas and corridors

It is proposed to install standard grid tile ceilings generally in all other areas of the building (with the exception of unoccupied spaces such as plant rooms). We would expect the reverberation time requirements of BB93 to be met provided the ceilings tiles used meet absorption Class A,B or C and are installed over the whole ceiling area in each space.


APPENDIX A – TECHNICAL TERMS AND UNITS IN RATING NOISE

General units and quantities

Decibel (dB) - This is the unit used to measure sound. The human ear has an approximately logarithmic response to sound over a very large dynamic range -

typically from 0.0002 to 200 Newtons per square metre (N/m2). Decibels provide a logarithmic scale to describe sound pressure and sound power levels. The threshold of hearing for most people corresponds to a sound pressure level of 0 dB and the threshold of aural pain to a sound pressure level of 140 dB.

Loudness and addition of decibels - Because of the logarithmic scale, decibels do not add in a linear fashion. When two identical sounds occur simultaneously, the resulting level is only 3 dB higher than for a single source. By contrast, an increase of 10 dB normally represents a doubling of “loudness” of the sound. Hence doubling the amount of sound energy results in very much less than a doubling in subjective loudness.

Sound Power Level (Lw or PWL) - This is a function of the noise source alone, and is independent of its surroundings. It is a measure in decibels of the amount of sound power emitted by the source.

Sound Pressure Level (Lp or SPL) - This is a function of the source and its surroundings and is a measure in decibels of the total instantaneous sound pressure at a point in space. The SPL can vary both in time and in frequency. Different measurement parameters are therefore required to describe the time variation and frequency content of a given sound. These are described below.

Assessment of non-steady sound

Most sounds are not steady, so that the sound pressure level fluctuates with time. A measurement is therefore meaningless unless we know whether it represents a minimum, maximum or some kind of time-averaged level. Various parameters have been derived to measure sounds of differing characters, and the most relevant to this report are as follows:

Leq,T The equivalent continuous noise level is used widely to measure noise

that varies with time. It is defined as the notional steady noise level that would contain the same acoustic energy as the varying noise. Because the averaging process used is logarithmic, the Leq,T level tends to be dominated

by the higher noise levels measured.

L90,T and L95,T These are the sound pressure levels exceeded for 90%

and 95% of the measurement period T. They are indications of the lowest noise levels during the measurement period, and is widely used to measure background noise and to assess inaudibility.

Lmax This is the maximum level measured, and is used to assess sleep

disturbance from intermittent sources such as aircraft and train noise. Lmax

is normally defined as the maximum reading given by a sound level meter set to “Fast” response (with a 0.125 second time constant).


0

10

20

30

40

50

60

70

80

90

31.5 63 125 250 500 1k 2k 4k 8k

SP

L, d

B

Octave Band Frequency, Hz

Noise Rating Curves NR20 to NR40

NR20

NR25

NR30

NR35

NR40

Frequency content and weighting

Octave and One-Third Octave Bands - The human ear is sensitive to sound over a frequency range of approximately 20 Hz to 20,000 Hz (1 Hz = 1 cycle per second), and is generally more sensitive to medium and high frequencies than to low frequencies. To define the frequency content of a noise, the spectrum is divided into frequency bands, the most common of which are octave bands, in which the mid frequency of each band is twice that of the band below it. For some applications, each octave band may be split into three one-third octave bands, and for finer analysis narrow band filters may be used.

'A' Weighting - A number of frequency weightings have been developed to imitate the ear's varying sensitivity to sound of different frequencies. The most commonly used is the 'A' weighting. The 'A' weighted SPL can be measured directly or derived from octave or one-third octave band SPLs. The result is a single figure index which gives some idea of the subjective loudness of the sound, but which contains no information as to its frequency content. The addition of the subscript “A” to any of the indices described above indicates that these have been measured using the ‘A’ weighting (e.g. LAeq,T or LAmax).

Noise Rating (NR) and other curves - 'A' weighted levels can not be used to define a spectrum or to compare sounds of different frequencies. NR curves convey frequency information in a single-figure index by defining the highest measured or specified level at each frequency. To measure the noise rating of a given environment, the SPL is measured in octave or one-third octave bands and the noise rating is then the highest NR curve touched by the measured levels. The graph below shows curves NR20 to NR40.

NC curves are similar to NR curves and are more commonly used outside Europe. They are not defined at 31.5 Hz.

NR and NC curves were derived theoretically from the response of the human ear under laboratory conditions. More recent research has found that at low noise levels, noise spectra matching these curves

allow too much noise at very high and very low frequencies compared with the levels at mid-frequencies. PNC curves have begun to be used more widely in the USA and UK for noise control in concert halls and theatres.


APPENDIX B - MEASURING EQUIPMENT AND CALIBRATION

Job reference and title: 11291 / 1 The Wherry School, Norwich

Measurement location: Hewitt School site, Norwich

Measurement date(s): 8 March 2016 09:00 – 11:00

Measuring equipment used:

Equipment description / serial number

Type number

Manufacturer Date of calibration expiration

Calibration certificate number

Precision sound level meter serial no. A2A-08643-E0

XL2-TA NTi Audio 23/10/2016 -

Microphone serial no. 9185

MC230 NTi Audio 23/10/2016 -

Microphone pre-amplifier serial no. 3489

MA220 Neutrik 23/10/2016 -

Microphone calibrator serial no. 25993

1251 Norsonic 28/10/2016 17328

Precision sound level meter serial no. 31634

118 Norsonic 18/11/2016 17448

Microphone serial no. 59932

1225 Norsonic 18/11/2016 17446

Microphone pre-amplifier serial no. 30583

1206 Norsonic 18/11/2016 17448

Microphone calibrator serial no. 31279

1251 Norsonic 18/11/2016 17447

Calibration level: 113.8dB @ 1kHz

Person in charge of measurements:

Joe Bear MIOA

Other persons present: Scott Blair, Kier

Principal sound source Traffic on road surrounding site

Measurement parameters Leq, 5mins in octave bands

Weather conditions: Overcast, 5 deg. Wind approx 7 mph


APPENDIX C - SPECIALIST ACOUSTIC MATERIALS AND SUPPLIERS

Note – this is not a comprehensive list as there are many suppliers in the UK, but the following are all known to supply products suitable for this project:

Sound insulating and absorbing suspended ceilings

Combison Duo by Saint Gobain Ecophon Ltd Tel: 01256 850 977 Fax: 01256 850 600 www.ecophon.co.uk

Sonar dB 44 by Rockfon Ltd Tel: 01656 864696 Fax: 01656 864549 www.rockfon.co.uk

Soundblocker 25 overlay tiles by Sound Reduction Systems Tel: 01204 380 074 Fax: 01204 380 957 www.soundreduction.co.uk

Perforated plasterboard ceilings

Gyptone and Rigitone by British Gypsum Ltd Tel: 08705 456123 Fax: 08705 456356 www.british-gypsum.co.uk

Apertura by Knauf Drywall Tel: 0800 521 050 Fax: 0800 521 205 www.knaufdrywall.co.uk

Impact-resistant acoustic panel manufacturers:

Super G by Saint Gobain Ecophon Ltd Tel: 01256 850 977 Fax: 01256 850 600 www.ecophon.co.uk

Steelsorba by Soundsorba Ltd, Tel: 01494 536888 Fax: 01494 536818 www.soundsorba.com/

Evo-Panel by Oscar Acoustics Tel: 01474 873122 Fax: 01474 879554 www.oscar-acoustics.co.uk

VertiQ by Rockfon Ltd Tel: 01656 864696 Fax: 01656 864549 www.rockfon.co.uk

http://www.ecophon.co.uk/

http://www.rockfon.co.uk/

http://www.soundreduction.co.uk/

http://www.british-gypsum.co.uk/

http://www.knaufdrywall.co.uk/

http://www.ecophon.co.uk/

http://www.soundsorba.com/

http://www.oscar-acoustics.co.uk/

http://www.rockfon.co.uk/

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