planning stage environmental noise assessment brooke weston … · 2019. 5. 7. · reverberation...

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Registered Number 04507219 – VAT No. 154 765 781

Planning Stage Environmental Noise Assessment

Brooke Weston Science Academy

Coomb Road, Kettering

NN15 7AA

Stroma Built Environment Ltd.

SBE Ref: 131747 – AC - 1v1

Stroma Built Environment. The Maltings, 81 Burton Road, Sheffield S3 8BZ

stroma.com/built-environment

0114 272 3004 | [email protected]

Registered in England: 04507219 | VAT No: 154765781

Brooke Weston Science Academy, Coomb Road, Kettering


SBE Ref. 131747 AC 1v1

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I. Revision History

Revision Date Description

1v1 13/02/2019

First Issue

Compiled By Authorised By

Samuel Sumner AMIOA

Graduate Acoustic Consultant

Tom Chaffer MIOA

Senior Acoustic Consultant

This report shall not be reproduced except in full and with the written approval of Stroma Built Environment Ltd.








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II. Executive Summary

Stroma Built Environment (SBE) has been appointed to undertake a planning stage noise assessment for a

proposed teaching block at the existing Brooke Weston Science Academy, Kettering.

A baseline noise survey has been undertaken at the site to establish prevailing noise levels.

Commentary on the effects of ventilation on internal noise levels has been provided, having reference to

relevant national guidance.

Ventilation for the standard classroom and teaching spaces at ground, first and second floor will require an

alternative means of ventilation, such as passive acoustically attenuating façade ventilators or a mechanical

ventilation system to allow windows to remain closed for ordinary ventilation.

Mitigation of overheating for standard classrooms during the hottest 200 hours of the year could be

achieved through the use of opening windows throughout the development.

At this stage in the development, details regarding items of fixed plant are not available. Therefore, noise

limits for external noise emission at the location of the closest Noise Sensitive Receptor (NSR) have been

proposed based on SBE’s measured background sound levels. Advice for the control of fixed plant noise in

teaching spaces is also provided.

Assessment indicates that with suitable specification of building façade elements and ventilation strategy the

proposed new building is capable of meeting the acoustic requirements for a school building set out in

Building Bulletin 93 (BB93).

Noise survey results, site observations, and noise assessment indicate that typical operational noise due to

the proposed expansion of the Brooke Weston Science Academy is not predicted to have a significant noise

impact on the local area or identified noise sensitive receptors.








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III. Contents

I. Revision History 2

II. Executive Summary 3

III. Contents 4

1. Introduction 5

2. Relevant Acoustic Standards 6

3. Baseline Noise Survey 9

4. Building Envelope 11

5. Operational Noise Impact 15

6. Conclusions 17

Appendix I. Survey Information and Data 18

Appendix II. Site Layout Plan 20

Appendix III. Acoustic Glossary 21

Appendix IV. Report Conditions 23








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1. Introduction

1.1 Stroma Built Environment (SBE) has been appointed by Willmott Dixon Construction (the Client) to

undertake acoustic consultancy services for a proposed new teaching block located within the

grounds of the existing Brooke Weston Science Academy in Kettering.

1.2 The new teaching block will contain a number of general classrooms, ICT classrooms, a library and

other ancillary spaces, over three storeys.

1.3 As a new school building, the development shall normally be required to meet Requirement E4 of Part

E of Schedule 1 to the building regulations 2010 which, as outlined in Section 8 of Approved

Document E 2003 including amendments up to 2015, will be to meet the values for sound insulation,

reverberation time and internal ambient noise given in Building Bulletin 93 Acoustic Design of

Schools: Performance Standards (BB93).

1.4 The purpose of this report is to provide design advice with regards to satisfying the BB93

requirements for internal ambient noise levels. The report will consider the acoustic impact of the

existing noise climate on the new teaching/learning spaces.

1.5 This document has been prepared for the sole use, benefit and information of the client for the

purposes set out in the document or instructions commissioning the works. The liability of SBE in

respect of the information contained herein shall not extend to any third party.

1.6 Whilst every effort has been made to ensure this report is easy to understand, it is technical in nature;

to assist the reader, a glossary of terminology is included in Appendix III.








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2. Relevant Acoustic Standards

National Planning Policy Framework

2.1 The current planning guidance for the assessment of the potential environmental noise impact is

outlined in the National Planning Policy Framework (NPPF). Whilst the NPPF does not set criteria that

must be achieved, the NPPF states the following in relation to the appropriate control of potential

noise impacts (paragraph 109):

2.2 “The planning system should contribute to and enhance the natural and local environment by

preventing both new and existing development from contributing to or being put at unacceptable risk

from, or being adversely affected by unacceptable levels of soil, air, water or noise pollution or land

instability…”

2.3 Therefore the policy requires that new developments are not affected to an unacceptable degree by

environmental noise.

Noise Policy Statement for England

2.4 The Noise Policy Statement for England (NPSE) provides further guidance on the Government’s

policy with regard to the potential impacts of noise. The NPSE states the aims of Government policy

relating to noise are:

2.5 “Through the effective management and control of environmental, neighbour and neighbourhood

noise within the context of Government policy on sustainable development:

• avoid significant adverse impacts on health and quality of life;

• mitigate and minimise adverse impacts on health and quality of life; and

• where possible, contribute to the improvement of health and quality of life”

2.6 The Explanatory Note to the NPSE provides further guidance on how significant noise effects should

be determined. The concepts of No Observed Effect Level (NOEL), Lowest Observed Adverse Effect

Level (LOAEL – the lowest noise level at which an adverse effect can be observed) and Significant

Observed Adverse Effect Level (SOAEL – the noise level above which significant adverse effects on

health and quality of life can be observed) are introduced, however the NPSE also states that:

2.7 “It is not possible to have a single objective noise-based measure that defines SOAEL that is

applicable to all sources of noise in all situations. Consequently, the SOAEL is likely to be different for

different noise sources, for different receptors and at different times.”








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Part E Building Regulations – BB93 Acoustic Performance Standard for Teaching Spaces

2.8 Section 8 of Approved Document E states that the normal way of satisfying Requirement E4 of Part E

to Schedule 1 of the Building Regulations 2010 for new school buildings is to meet the performance

standards set out in Building Bulletin 93 ‘Acoustic design of schools: performance standards’ (BB93).

2.9 Section 1.1 of BB93 presents Indoor Ambient Noise Level upper limit criteria (IANL) for various types

of teaching, study and ancillary spaces. Teaching spaces intended specifically for students with

special hearing and communication needs is to achieve a maximum IANL of 30 dB LAeq,30mins. In

addition BB93 states that the indoor ambient noise level should not regularly exceed 60 dB LA1,30min.

2.10 Note that the BB93 IANL criteria include contributions from external sources outside the school

premises and building services noise but exclude contributions from teaching activity/equipment, staff

and students within the school premises.

Department for Education - Advice on standards for school premises

2.11 Pupils with special needs may need to be taught in spaces with lower noise levels and shorter

reverberation times than in mainstream classrooms and class bases. Special schools and SEN units

in mainstream schools therefore require designing to a higher acoustic standard. Where pupils with

these special needs are taught in mainstream schools, the acoustics of the spaces where they are

taught may need to be enhanced to the same standards as those in special units.

Equality Act 2010

2.12 The aspects that are relevant to acoustics in schools are principally those relating to disabilities, and

where English is not the first language and clarity of speech is particularly important to assist

comprehension.

Control of External Noise Impact from Building Services

2.13 It is common for Local Authority planning requirements to require noise impact assessment. At the

time of writing HRS are not aware of any specific noise impact assessment requirements for planning,

however it is good practice to control noise from mechanical services to ensure minimal impact on

nearby noise sensitive properties. It is therefore recommended that noise from new building services

plant does not exceed the representative background noise level when assessed at the nearest noise

sensitive receptor when assessed in line with BS 4142:2014 ‘Methods for rating and assessing

industrial and commercial sound’ (BS 4142). This represents a BS 4142 assessment of ‘low impact’.








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BS 4142:2014 ‘Methods for rating and assessing industrial and commercial sound’ (BS 4142)

2.14 BS 4142 describes a method for assessing the likelihood of complaints from noise sources that are of

an industrial nature (e.g. fans, pumps, chillers, air handling units etc.). The assessment methodology

is based upon determining a ‘rating level’ for the equipment being assessed, which is the level of

noise from the item or items of plant being assessed (measured as LAeq).

2.15 The rating level is then compared with the underlying background noise level (measured as LA90) in

the absence of noise from the item or items of plant being assessed.

• A difference of around +10 dB or more is likely to be an indication of a significant adverse impact,

depending on the context.

• A difference of around +5 dB is likely to be an indication of an adverse impact, depending on the

context.

• The lower the rating level is relative to the measured background sound level, the less likely it is

that the specific sound source will have an adverse impact or a significant adverse impact.

Where the rating level does not exceed the background sound level, this is an indication of the

specific sound source having a low impact, depending on the context.

2.16 BS 4142 states that a penalty should be added for any plant which gives rise to noise features that

may increase disturbance such as tonal, impulsive or intermittent characteristics. With respect to the

acoustic feature correction, BS 4142 states:

2.17 “Certain acoustic features can increase the significance of impact over that expected from a basic

comparison between the specific sound level and the background sound level. Where such features

are present at the assessment location, add a character correction to the specific sound level to

obtain the rating level.”

2.18 Generally a rating penalty for a sound should be based on a subjective assessment of its

characteristics.








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3. Baseline Noise Survey

3.1 A baseline noise survey was undertaken at the site in order to establish prevailing noise levels at the

façade location of the proposed new building, and to establish background noise levels in the vicinity

of nearby noise sensitive receptors. Long term noise measurements were undertaken between

Monday 4th and Tuesday 05

th February 2019. Additional short term monitoring was undertaken during

the afternoon of Monday 04th February 2019. The existing site layout and noise monitoring positions

are illustrated on Figure 2.

Figure 2: Approximate site monitoring location plan








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3.2 All measurements were undertaken under free field conditions using a Class 1 sound level meter. The

sound level meter was mounted on a tripod, and fitted with weather protection throughout the duration

of the survey. Weather conditions throughout the initial survey period were fine and dry, with wind

speeds generally < 5 ms-1

.

3.3 The noise climate at the site was controlled by noise from the Deeble Road, which lies approximately

20 m north of the existing academy building.

3.4 Table 1 presents a summary of the measured noise levels, whilst detailed noise data is presented in

Appendix I.

Table 1: Summary of noise survey measurements

Measurement

Position Period

Measured sound pressure level

LAeq, T[1]

LA1,T[2]

LA90,T[2]

LT

12:55 – 23:00 52 62 46

23:00 – 07:00 43 51 38

ST 12:45 – 14:30 62 69 55

Notes to Table 1: [1]

Logarithmic average over stated period. [2]

Arithmetic average over stated period.

3.5 The closest noise sensitive receptors (NSR) to the site are understood to be residential dwellings to

the south of the existing academy building along Greenbank Avenue.

3.6 The identified NSRs are described in Table 2.

Table 2: Identified NSR

NSR Description Distance from site

A Residential dwellings along Greenbank Avenue 120 m








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4. Building Envelope

4.1 There are a range of indoor ambient noise level (IANL) criteria defined in BB93 for different spaces

with the ventilation scheme operating under normal conditions. Where a natural or hybrid ventilation

strategy is operating, in particular circumstances, there is an additional allowance of +5 dB over and

above the identified criteria.

4.2 For the purposes of this assessment, the acoustically sensitive internal room space types have been

classified according to Section 1.1 of BB93. It is recommended that these are checked as being

suitably classified according to Building Control and End-Client requirements. It is understood that the

development does not include spaces specifically for use in teaching students with Special

Educational Needs (SEN).

4.3 The BB93 classifications for the purposes of this report are given below.

Table 3: Proposed BB93 room classifications

Room Type BB93 Classification Upper limit for indoor ambient

noise levels (dB LAeq, 30min)

Conference Room Meeting Room ≤ 401

Interview Room Meeting Room ≤ 401

Deputy Office Office ≤ 401

Staff Work Prep Study Room (Teacher preparation) ≤ 401

Dining Area/Common Room Dining Room ≤ 45

ICT (Resource) / Library / Study

Area Resource Area / Study Area ≤ 40

1

Small Group Room Secondary school classrooms

≤ 351

General Classroom ≤ 351

Class & Central Resources Resource Area ≤ 401

ICT Classroom ICT Room ≤ 401

Kitchen Kitchen 2 ≤ 50

WC Toilets 2 ≤ 50

Notes to Table 3:

1. The upper limit for the indoor ambient noise level may be increased by 5 dB when natural/hybrid ventilation limits the daily

average carbon dioxide concentration to no more than 1,500ppm with the maximum concentration not exceeding 2,000ppm for

more than 20 consecutive minutes on any day, as described in BB93 Section 0.8 Acoustics and ventilation.

2. Approved Document E in support of the Building Regulations 2010 applies to teaching and learning spaces and is not

intended to cover administration and ancillary spaces except in as far as they affect conditions in neighbouring teaching and

learning spaces. For these areas performance standards are for guidance only.








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Building Envelope Sound Insulation Performance

4.4 The building envelope is required to provide adequate sound reduction of external noise levels to

achieve the internal design criteria. Noise levels from SBE’s noise survey summarised in Section 3

have been used to inform the building envelope requirements with regards to external noise intrusion.

4.5 At this stage in the development, proposals for the build-up of the walling sections of the façade have

not been confirmed. Based on the measured external noise levels, the sound reduction

performances outlined in Table 4 are expected to satisfy the IANL criteria, with windows closed.

Table 4: Minimum facade insulation requirements

Building element Minimum sound reduction index

Façade walling 40 dB Rw + Ctr

Roof 28 dB Rw + Ctr

Glazing 27 dB Rw + Ctr

4.6 Specifications for façade insulation should be reviewed at the detailed design stage once the

proposed build-up has been established to ensure that the IANL can be satisfied.

4.7 Assessment assuming typical façade constructions indicates that generally thermal double glazing

with a sound insulation of ≥ 27 dB Rw + Ctr is suitable for the scheme. This can typically be achieved

with a standard thermal build-up of two panes of 6 mm glazing separated by a 16 mm void.

Roof Construction

4.8 The roof construction must provide adequate sound insulation to prevent external noise break-in from

existing background noise sources. At this stage in the development, the proposed roof build up has

not been determined, however a minimum sound insulation performance of 28 dB Rw + Ctr is

recommended to avoid an increase in IANL at second floor level.

Ventilation

4.9 Section 1.1.3 of BB93 addresses natural and hybrid (natural/mechanical) ventilation in schools and

states that a 5 dB relaxation of BB93 indoor ambient noise levels is applicable in teaching spaces

when the proposed ventilation systems are operating in their normal condition. The normal condition

is defined below:

4.10 “The normal condition for a ventilation system in natural or hybrid mode is defined as when the

system is operating to limit the daily average carbon dioxide concentration to no more than 1,500ppm

with the maximum concentration not exceeding 2,000ppm for more than 20 consecutive minutes on

any day. This would normally equate to a minimum ventilation rate of approximately 8 l/s per person.”








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4.11 BB93 states:

4.12 “Where external ambient free field noise levels at the facade expressed as the LAeq,30mins, do not

exceed the IANL figures given in Table 1 (of BB93) by more than 16 dB for single sided and 20 dB for

cross ventilated or roof ventilated spaces, the criteria for natural ventilation can usually be achieved.”

4.13 Based on external free field noise measurements taken by SBE, the north, east and west building

elevations are expected to be exposed to noise levels of ≤ 65 dB LAeq, 30min. Based on these levels, it

is expected that indoor ambient noise levels within standard classrooms and general teaching areas

would exceed BB93 indoor ambient noise level criterion with ventilation via open windows.

4.14 Standard classrooms on the southern façade are predicted to be exposed to noise levels less than 50

dB LAeq, 30min. A scheme of natural ventilation incorporating partially opened windows would be

suitable to satisfy the IANL’s.

4.15 Where ventilation via open windows is not feasible BB93 IANL criteria can be satisfied with ventilation

provided by an acoustically attenuated passive ventilators or full mechanical system.

4.16 If passive ventilation via façade mounted ventilators is preferred for teaching spaces then calculations

indicate that BB93 complaint indoor noise levels can be achieved with ventilators providing a

minimum sound insulation performance of 32 dB Dn,e,w. This is based on a maximum of two

ventilators per classroom. Increasing the number of facade ventilators per rooms requires an

increased sound insulation for each unit, and should be reviewed against ventilation requirements.

4.17 Calculations indicate that non classroom spaces on the northern façade such as Interview Rooms,

Conference Rooms and Staff Work Rooms would also exceed BB93 IANL requirements with

ventilation by open windows. BB93 complaint indoor noise levels are predicted to be achieved with a

ventilator providing a minimum sound insulation performance of 32 dB Dn,e,w. This is based on a

single ventilator per room. Increasing the number of facade ventilators per rooms requires an

increased sound insulation for each unit, and should be reviewed against ventilation requirements.

4.18 Facades of the library at ground floor are predicated to be exposed to noise levels of ≤ 60 dB

LAeq,30min. Typically a partially open window will provide an attenuation of 14 – 17 dB; therefore a

scheme of natural ventilation incorporating partially opened windows may be sufficient to satisfy the

IANL’s, depending on ventilation open area requirements and proposed window types.

4.19 Ventilation to toilets and ancillary areas with IANL of ≤ 50 dB LAeq, 30min can be achieved through the

use of partially open windows on all facades.








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Intermittent Boost and Mitigation of Summertime Overheating

4.20 BB93 provides separate guidance for intermittent boost ventilation and additional airflow to mitigate

overheating. When providing intermittent boost ventilation and when operating to control summertime

overheating during the hottest 200 hours of the year (including the summer holiday), natural and

hybrid ventilation systems (with open windows / vents) IANLs due to external noise ingress should not

exceed 55 dB LAeq, 30mins.

4.21 Typically an open window used to provide short term increased ventilation or mitigate overheating

would provide an attenuation of approximately 10 dB. It is therefore considered feasible that open

windows could be used for intermittent boost ventilation and to control summertime overheating

during the hottest 200 hours of the year (including the summer holiday) throughout the proposed new

building.








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5. Operational Noise Impact

Control of Building Services External Noise

5.22 It is good practice to control noise from mechanical services to ensure minimal impact on nearby

noise sensitive properties so as to reduce risk of noise disturbance and potential complaint.

5.23 At this point in the development, the location and type of fixed plant which may be associated with the

proposed new teaching block has not been confirmed. Therefore, suitable noise limits to which all

items of fixed plant should adhere have been set based on the results of SBE’s long term noise

measurements in the vicinity of the nearest NRSs having regard to the guidance in BS 4142 outlined

in Section 2.

5.24 Wherever possible, the general principal of reducing the level of noise at source is recommended as

the best way of reducing noise impact. Where this measure on its own may not be sufficient,

additional suitably designed mitigation measures such as noise barriers, lagging materials, or

acoustic attenuators/louvres may be used to control the plant noise in order to achieve the required

rating level.

5.25 Table 5 presents the proposed fixed plant noise limits based on a modal analysis of the day and night

time background noise levels.

Table 5: Recommended BS 4142 fixed plant noise limits

NSR Period

Representative background sound level

(dB LA90,T)

Proposed rating noise level

(dB LAr,Tr)

All NSRs

Daytime

(07:00-23:00) 44 ≤ 44

Night

(23:00-07:00) 35 ≤ 35

Notes to Table 5: Time period T is equal to 60 minutes during the day, and 15 minutes during the night time.

5.26 Mechanical services noise emissions will also need to be suitably controlled to limit noise impact upon

external teaching areas to be no more than 50 dB LAeq,T.

5.27 To limit the risk of noise disturbance to teaching activities in internal spaces, external building

services noise should be designed such that the atmospheric noise level outside an openable

window, ventilation louvre or other facade opening into a teaching space, does not exceed 45 dB

LAeq,T at all times. Manufacturers’ noise data for proposed plant selections should be reviewed to

ensure that the above criterion is met.








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Operational Noise Impact

5.28 The new expansion building is of limited size in comparison to the existing school building on the site,

therefore it is anticipated that the increase in pupil numbers on the school site will be small and is not

expected to lead to a significant increase in operational noise levels.

5.29 Generally a doubling in the volume of road traffic results in a 3 dB increase in traffic noise. Due to

existing traffic levels on local roads, it is not anticipated that any changes in local traffic due to the

new school would lead to a perceptible change in traffic noise in the local area.

5.30 There are other factors that are likely to mitigate any additional noise impact due to the operational

activity of the scheme, including:

• Audible road traffic noise across the site and surrounding area

• Existing operational school site with no significant change to pupil numbers

• No expansion of existing on-site parking








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6. Conclusions

6.1 Stroma Built Environment has been appointed to undertake a planning noise assessment for a

proposed new teaching block extension to the existing Brooke Weston Science Academy in Kettering.

6.2 A noise survey has been undertaken by SBE to establish noise levels at the site, and in the vicinity of

nearby noise sensitive receptors. The noise climate at the site was found to be controlled primarily by

road traffic noise from Deeble Road, approximately 20 m north of the existing academy building.

6.3 The measured noise levels have been used to inform the ventilation and façade insulation strategy for

the identified teaching spaces within the proposed extension.

6.4 Ventilation for the standard classrooms and general teaching areas at ground, first and second floor

of the southern façade can be achieved through a scheme of natural ventilation, incorporating

partially open windows.

6.5 Standard classrooms and general teaching areas on the north, east and western façades will require

an alternative means of ventilation, such as mechanical ventilation or acoustically attenuated

ventilators to allow windows to remain closed for ordinary ventilation.

6.6 Based on typical attenuation for an open window, intermittent boost ventilation and mitigation of

overheating during the hottest 200 hours of the year could be achieved through the use of open

windows throughout the scheme.

6.7 At this stage in the development, details regarding items of fixed plant are not available. Therefore,

noise limits for external noise emission at the location of the closest NSR have been proposed based

on SBE’s measured background noise levels. Advice for the control of fixed plant noise in teaching

spaces is also provided.

6.8 Consideration of operational noise due to the expansion of the Brooke Weston Science Academy

suggests that there will be no significant increase in operational noise due to the wider school site.








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Appendix I. Survey Information and Data

Figure A1: Noise level time history plot at Long Term measurement position


stroma.com/built-environment 0114 272 3004 | [email protected]





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Table A1: Measurement summary of Short Term measurement position

Start Date and Time

Duration Measured Sound Pressure Level (dB)

LAeq,T LA01,T LA90,T

04/02/2019 12:45 0:04:54 62.1 68.3 53.9

04/02/2019 12:50 0:05:00 62.3 70.6 57.4

04/02/2019 12:55 0:05:00 61.8 67.2 58.1

04/02/2019 13:00 0:04:58 62.7 72.7 53.1

04/02/2019 13:05 0:04:54 62.9 69.2 59.1

04/02/2019 13:10 0:05:00 60.9 67.4 54.0

04/02/2019 13:15 0:05:00 61.4 71.0 53.9

04/02/2019 13:20 0:05:00 62.5 69.1 58.0

04/02/2019 13:25 0:04:58 61.8 69.9 55.3

04/02/2019 13:30 0:04:58 62.1 67.3 53.9

04/02/2019 13:35 0:04:55 63.2 71.1 58.7

04/02/2019 13:40 0:05:00 61.6 66.3 55.4

04/02/2019 13:45 0:05:00 60.6 67.3 52.8

04/02/2019 13:50 0:04:52 63.5 73.1 59.2

04/02/2019 13:55 0:04:51 61.5 72.2 54.1

04/02/2019 14:00 0:04:44 60.8 67.9 54.2

04/02/2019 14:05 0:05:00 61.1 67.6 56.4

04/02/2019 14:10 0:05:00 62.4 68.4 56.7

04/02/2019 14:15 0:05:00 62.0 67.9 55.7

04/02/2019 14:20 0:05:00 63.0 69.0 55.7

04/02/2019 14:25 0:05:00 63.8 70.0 60.1

04/02/2019 14:30 0:00:41 64.4 67.4 63.2






Planning Design Report


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Appendix II. Site Layout Plan

Figure A2: Floor plan of Ground Floor








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Appendix III. Acoustic Glossary

Sound pressure level and the decibel, dB

A sound wave is a small fluctuation of atmospheric pressure. The human ear responds to these variations in

pressure, producing the sensation of hearing. The ear can detect a very wide range of pressure variations. In

order to cope with this wide range of pressure variations, a logarithmic scale is used to convert the values into

manageable numbers. The decibel is the logarithmic unit used to describe sound (or noise) levels. The usual

range of sound pressure levels is from 0 dB (threshold of hearing) to 120 dB (threshold of pain).

Frequency and hertz, Hz

Frequency is a measure of the rate of fluctuation of a sound wave. The unit used is cycles per second, or

hertz (Hz). Sometimes large frequency values are written as kilohertz (kHz), where 1 kHz = 1000 Hz. The

human range of hearing is commonly accepted to be 20 Hz to 20,000 Hz. Additionally, an octave can be used

to describe the interval between a frequency in Hz and either half or double that frequency.

Frequency weighting

Different weighting networks can be applied to a given sound level in each stated octave band by a specified

amount, in order to better represent the response of the human ear. The most commonly used weighting

network is the ‘A’ weighting, and the letter ‘A’ will be included within a descriptor to indicate that the value has

been ‘A’ weighted, e.g. LAeq,T or LA90. An ‘A’ weighted noise level may also be written as dB(A). Other

weightings less commonly used are ‘C’ and ‘D’ weighting.

Noise indices

When a noise level varies with time, the measured ‘A’ weighted dB level will vary as well. In this case it is

therefore not possible to represent the noise climate with a simple ‘A’ weighted dB value. In order to describe

noise where the level is continuously varying, a number of other indices, including statistical parameters, are

used. The various indices used are described as below:

LAeq,T The ‘A’ weighted ‘equivalent continuous noise level’ which is an average of the total sound

energy measured over a specified time period, T

LAmax The maximum ‘A’ weighted noise level that was recorded during the monitoring period.

LA10 The ‘A’ weighted noise level that was recorded for at least 10% of the monitoring period.

LA90 The ‘A’ weighted noise level that was recorded for at least 90% of the monitoring period,

usually taken as the underlying ‘background’ noise level.

Sound level difference, D

The sound level difference between two internal spaces, or between internal and external spaces. The ‘D’

value is used to denote the differences at each third octave or octave band, with a single figure ‘weighted’

value to describe an overall performance. Note that the ‘D’ value will always describe an in-situ or on-site

acoustic performance. All values are described using the decibel.








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Dw Single figure weighted sound level difference, simply the measured source noise level minus

receiver noise level, not adjusted to reference conditions

DnT,w Weighted normalised sound level difference – a single, weighted sound insulation value,

normalised to a reference reverberation time using the measured reverberation time in the

receive room

DnT,w + Ctr As above, with a spectral adaptation term applied to account for the effects of low frequency

noise, and based on urban traffic noise

Dnf,w Overall flanking normalised level difference - A parameter that defines the flanking

transmission of sound from room to room where a dividing partition or floor construction abuts

a flanking building element common to both rooms, such as the building façade or ceiling

Sound reduction index, R

This describes the sound transmitted through a material or building element, such as a wall, door or window. It

is measured in a laboratory with suppressed flanking transmission. The ‘R’ value is used to denote the

differences at each third octave or octave band, with a single figure ‘weighted’ value to describe an overall

performance. All values are described using the decibel.

Rw Weighted single figure sound reduction index

Rw + Ctr As above, with a spectral adaptation term applied to account for the effects of low frequency

noise, and based on urban traffic noise

R’w The ‘apparent sound reduction index’, a field measurement to obtain the sound reduction

index of a material or element, with all effects of site installation accepted.

Standardised impact sound pressure level, L’nT,w

L’nT,w is the single figure used to characterise the impact sound pressure level in a receiving room, normalised

to a reference reverberation time. Impact noise can be classified as (but is not limited to) the result of footfall

impact on a separating floor to a habitable space below. All values are described using the decibel.








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Appendix IV. Report Conditions

This document has been prepared for the sole use, benefit and information of the Client. The liability of

Stroma Built Environment Ltd. in respect of the information contained herein will not extend to any third party

unless prior agreement is obtained in writing from Stroma Built Environment Ltd.

This report is limited to addressing the specific acoustic issues contained herein. Advice has been provided

for acoustic reasons only and it is recommended that appropriate expert advice be sought on all the

ramifications, e.g. safety, fire, structural, CDM etc., associated with any proposals contained herein.

The in-situ performance of acoustic measures is influenced to a large extent by the quality of workmanship

and compliance with the specifications on-site during construction, as such, Stroma Built Environment Ltd.

accepts no liability for issues with acoustic performance arising from such factors.

Acoustic survey and testing work carried out for the project is representative of the prevailing conditions at the

time of the work. Conditions can vary and no warranty is given as to the possibility of changes in the

environment of the site and surrounding area at differing times.

In particular, it should be noted that where calculations are carried out that are based on assumptions

regarding certain aspects where information has not been supplied, these are provided for indicative purposes

only and should be treated as such.

planning stage environmental noise assessment brooke weston … · 2019. 5. 7. · reverberation...

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