RP01-14545 - Sloane Crawley Properties Ltd - Ifield Road ... · 1.1 Cass Allen Associates has been instructed by Sloane Crawley Properties Ltd to assess the suitability of the site

NOISE IMPACT ASSESSMENT

27-45, IFIELD ROAD, CRAWLEY

SLOANE CRAWLEY PROPERTIES LTD

RP01-14545

NOISE IMPACT ASSESSMENT

PROJECT: IFIELD ROAD, CRAWLEY

CLIENT: SLOANE CRAWLEY PROPERTIES LTD

CLIENT ADDRESS: BERKELEY SQUARE HOUSE

BERKELEY SQUARE

MAYFAIR

LONDON

W1J 6BD

COMPANY ADDRESS: CASS ALLEN ASSOCIATES

BEDFORD I-LAB

PRIORY BUSINESS PARK

BEDFORD

MK44 3RZ

DOCUMENT CONTROL:

This report has been prepared by Cass Allen Associates Ltd with all reasonable skill, care and diligence, and taking account of the

resources devoted to it by agreement with the client. Information reported herein is based on the interpretation of data collected and has

been accepted in good faith as being accurate and valid. This report is for the exclusive use of the client named above; no warranties or

guarantees are expressed or should be inferred by any third parties. This report may not be relied upon by other parties without written

consent from Cass Allen Associates. Cass Allen Associates disclaims any responsibility to the client and others in respect of any matters

outside the agreed scope of work.

REVISION ISSUE DATE REPORT BY CHECKED BY NOTES

0 09 December 2014 Adam Bamford, BSc MIOA

DipIOA, Acoustics Consultant

Sam Bryant, MPhys AMIOA,

Acoustics Consultant

Draft issue for comment

1 18 December 2014 Adam Bamford, BSc MIOA

DipIOA, Acoustics Consultant

Sam Bryant, MPhys AMIOA,

Acoustics Consultant

Planning issue, incorporating comments from project team

Project: Ifield Road, Crawley Client: Sloane Crawley Properties Ltd Ref: RP01-14545

Web: www.cassallen.co.uk Tel: 01234 834 862

Page: 1 of 16

TABLE OF CONTENTS

1. INTRODUCTION

2. PROJECT DESCRIPTION

3. PLANNING POLICY

4. NOISE AFFECTING THE DEVELOPMENT

5. PLANT NOISE IMPACT ASSESSMENT

6. NOISE BREAKOUT FROM THE HOTEL PLANT ROOM

7. CONCLUSIONS

GLOSSARY

CURRENT DEVELOPMENT DRAWINGS

SURVEY RESULTS

CAA NOISE CONTOURS FOR A 2 RUNWAY FUTURE SCENARIO AT LONDON GATWICK AIRPORT

FACSIM CALCULATIONS



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1. INTRODUCTION

1.1 Cass Allen Associates has been instructed by Sloane Crawley Properties Ltd to assess the

suitability of the site located at 27-45 Ifield Road, West Green in Crawley for a proposed mixed use

redevelopment with respect to noise.

1.2 The assessment has been carried out in accordance with relevant local and national planning

guidance.

1.3 The aims of the assessment were:

To establish the suitability of existing noise levels at the site for the proposed

development; and

Where required, identify appropriate mitigation measures to achieve acceptable noise

levels in the finished development.

1.4 This report contains technical terminology; a glossary can be found in Appendix 1.



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2. PROJECT DESCRIPTION

2.1 The site currently contains a surface car park and is located in a predominantly residential area,

containing some commercial uses. The site is bounded to the north by West Green Drive, to the

east by a strategic roundabout that forms a link to Crawley town centre, to the south by Ifield Road

and to the west by existing two storey residential dwellings. The site is located approximately 3.5km

due south of Gatwick Airport.

2.2 An annotated site location plan is shown in Figure 1 below.

Figure 1 Annotated Site Location Plan

2.3 The proposals involve the redevelopment of the site to provide residential dwellings; including a

mixture of 1-bed and 2-bed apartments, an apart-hotel and associated car parking provisions.

Relevant current drawings of the proposed development layouts are shown in Appendix 2.

Site



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3. PLANNING POLICY

National Policy

3.1 Outline guidance for the assessment of noise affecting new developments is given in the National

Planning Policy Framework (NPPF). Section 109 of the NPPF states:

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…noise

pollution.

and in section 123:

Planning policies and decisions should aim to:

avoid noise from giving rise to significant adverse impacts on health and quality of life as

a result of new development;

mitigate and reduce… other adverse impacts on health and quality of life arising from noise

from new development, including through the use of conditions;

recognise that development will often create some noise and existing businesses wanting

to develop in continuance of their business should not have unreasonable restrictions put

on them because of changes in nearby land uses since they were established;

and identify and protect areas of tranquillity which have remained relatively undisturbed by

noise and are prized for their recreational and amenity value for this reason”.

Noise Policy Statement for England

3.2 The Noise Policy Statement for England (NPSE) was published in March 2010 and seeks to clarify

the underlying principles and aims in policy documents, legislation and guidance that relate to

noise. It also sets out the long term vision of Government noise policy:

To promote good health and a good quality of life through the effective management of

noise within the context of Government policy on sustainable development.

3.3 The NPSE clarifies that noise should not be considered in isolation of the wider benefits of a

scheme or development, and that the intention is to minimise noise and noise effects as far as is

reasonably practicable having regard to the underlying principles of sustainable development.

3.4 The explanatory note of NPSE defines the terms used in the NPPF:

2.20: There are two established concepts from toxicology that are currently being applied

to noise impacts, for example, by the World Health Organisation. They are:



Page: 5 of 16

NOEL – No Observed Effect Level

This is the level below which no effect can be detected. In simple terms, below this level,

there is no detectable effect on health and quality of life due to the noise.

LOAEL – Lowest Observed Adverse Effect Level

This is the level above which adverse effects on health and quality of life can be detected.

2.21: Extending these concepts for the purpose of this NPSE leads to the concept of a

significant observed adverse effect level.

SOAEL – Significant Observed Adverse Effect Level

This is the level above which significant adverse effects on health and quality of life occur.

3.5 The NPSE does not define the SOAEL numerically, stating in paragraph 2.22:

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. It is

acknowledged that further research is required to increase our understanding of what may

constitute a significant adverse impact on health and quality of life from noise. However,

not having specific SOAEL values in the NPSE provides the necessary policy flexibility

until further evidence and suitable guidance is available.

Local policy

3.6 Adopted local planning policy (consisting of the Core Strategy 2008 Revision and ‘saved’ policies

of the Crawley Local Plan 2000) seeks to ensure a high standard of design and amenity with all

new development, however does not provide detailed guidance on noise. However, the emerging

Local Plan includes planning policies to guide development within the borough in respect of noise

and Policy ENV11 (Development and Noise) is relevant to this application. Relevant excerpts of

this policy are stated below:

Noise Sensitive Development

Noise sensitive uses proposed in areas that are exposed to significant noise from existing

or future transport sources (air, road, rail and mixed sources) will be permitted where it

can be demonstrated that future users will not be exposed to an unacceptable noise

impact. Levels set out in the Local Plan Noise Annex will establish if the proposal is

acceptable in noise impact terms.

Mitigating Noise Impact

Where proposals are identified as being subject to significant or unacceptable noise

impact, either through noise exposure or generation, the best practical means of mitigation

must be employed to mitigate noise impact to an appropriate level. Proposals that do not

appropriately mitigate against unacceptable noise impact through the design and planning

process will be refused.



Page: 6 of 16

3.8 To address the requirements of the national and local policies, the following key acoustic matters

have been assessed:

Noise affecting the habitable areas of the proposed development;

Noise emissions from mechanical plant associated with the development at both the

position of existing sensitive receptors in the area and future dwellings associated with

the development itself; and

Noise breakout from the proposed hotel plant room to the guest rooms located above.

3.9 The above matters are discussed in turn in the following sections of this report.



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4. NOISE AFFECTING THE DEVELOPMENT

4.1 The noise levels that will exist within the habitable areas of the finished development have been

predicted based on the existing noise environment at the site and outline details for the design of

the development. The predicted noise levels have then been compared with appropriate design

criteria. Where the criteria have been predicted to be exceeded, suitable mitigation measures have

been identified.

Design criteria – Internal noise levels

4.2 Appropriate design criteria for acceptable noise levels in acoustically sensitive areas of new

developments are given in the Crawley Local Plan Noise Annex within Crawley 2030 – The Crawley

Borough Local Plan 2015-2030. The relevant design criteria for noise sensitive development

affected by noise from transport sources (which is applicable to this application) are summarised

in Table 1.

Table 1 Standards for Noise Sensitive Development Affected by Noise from Transport

Sources from the Noise Annex of Crawley Borough Council’s Local Plan



Page: 8 of 16

4.3 In addition to the above, British Standard 8233:2014 ‘Guidance on sound insulation and noise

reduction for buildings’ (BS8233) also provides up to date guidance on suitable internal noise levels

within buildings. This has been referred to where appropriate.

4.4 It is also considered appropriate in this case to assess the potential impact of noise emissions from

individual vehicle pass-bys on the bedrooms of the development during the night-time. This is in

line with guidance given in the World Health Organisation (WHO) document Guidelines for

community noise, which recommends that noise exceeding 45dB LAFmax should be limited, if

possible and that for a good sleep, it is believed that indoor sound pressure levels should not

exceed 45dB LAmax more than 10-15 times per night.

4.5 BS8233 also advises that it is desirable that noise levels in external amenity areas of residential

developments do not exceed 50 dB LAeq and that 55 dB LAeq,T should be regarded as a upper

guideline value. However, the Standard recognises that these guideline values will not always be

achievable in city centres or urban areas adjoining main roads or other transport sources. In these

cases, BS8233 advises that the development should be designed to achieve the lowest practical

noise levels in the amenity spaces.

4.6 The following acoustic design criteria have therefore been adopted for the development:

Average noise levels in living rooms and dining rooms during the day should not exceed

35 dB LAeq,0700-2300hrs and 40 dB LAeq,0700-2300hrs respectively;

Average noise levels in bedrooms should not exceed 35 dB LAeq,0700-2300hrs during

the day 30 dB LAeq,2300-0700hrs during the night;

Maximum noise levels should not regularly exceed 45 dB LAmax in bedrooms during the

night;

Where possible, average noise levels in external amenity areas during the day should be

lower than 50-55 dB LAeq,0700-2300hrs.

Existing site noise levels

4.7 A noise survey was carried out at the site between 18th and 19th November 2014 to assess typical

existing noise levels in the area. The full methodology and results of the noise survey are provided

in Appendix 3.

4.8 Average noise levels (LAeq) across the site were generally dictated by road traffic on West Green

Drive and Ifield Road. Background noise levels (LA90) across the site were dictated by constant

road traffic noise from the surrounding road network.

4.9 Maximum noise levels (LAFmax) along the northern and southern site boundaries were dictated

by individual vehicle movements on West Green Drive and Ifield Road respectively.

4.10 Measurable noise from aircraft movements was not identified during the survey. Furthermore, the

site lies outside the noise contours produced by the Civil Aviation Authority for a 2 runway future

scenario at London Gatwick airport (see Appendix 4). Therefore, in our view, noise from aircraft

associated with London Gatwick airport will be insignificant in comparison to road traffic noise.



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4.12 The noise survey results show that the northern boundary of the site directly overlooking West

Green Road will be subject to the highest incident noise levels. Existing typical free-field noise

levels at this position (measurement position L1 – Appendix 3) are as follows:

Average noise levels during the daytime - 67 dB LAeq,0700-2300hrs;

Average noise levels during the night-time - 58 dB LAeq,2300-0700hrs;

Typical maximum noise levels during the night-time - 80 dB LAFmax.

4.13 The southern boundary of the site directly overlooking Ifield Road was found to be subject to lower

incident noise levels than the northern boundary. Existing typical free-field noise levels at

measurement position L2 are as follows:

Average noise levels during the daytime - 64 dB LAeq,0700-2300hrs;

Average noise levels during the night-time - 57 dB LAeq,2300-0700hrs;

Typical maximum noise levels during the night-time - 75 dB LAFmax.

Internal noise levels in noise-sensitive rooms

4.14 Full construction details for the development have not been finalised as the project is at an early

design stage. It has therefore been assumed that the external walls of the development will be

constructed using a standard masonry construction (e.g. 102mm brick, 100mm insulated cavity,

100mm concrete block) or a light-weight construction designed to achieve a similar level of sound

insulation (this is technically achievable subject to detailed design). Consequently, internal noise

levels would be dictated by external noise ingress via glazing and ventilators.

4.15 The ventilation scheme for the project has not yet been decided and therefore, for the purpose of

the assessment, it has been assumed that the residential units will be ventilated via a continuous

mechanical extract system in wet rooms and background ventilators in the external facades, with

openable windows for the provision of purge ventilation (as per System 3 from Building Regulations

Part F).

4.16 It is assumed that the ventilation scheme for the proposed hotel will be Mechanical Ventilation with

Heat Recovery (MVHR) i.e. System 4 from Building Regulations Part F. Therefore, there will be no

background ventilators in the external façades of the hotel (e.g. trickle ventilators etc).

4.17 The MVHR system should be selected to ensure that noise from air supply and extract ductwork

does not exceed acceptable levels within habitable rooms. Appropriate specifications for noise

levels from the MVHR system (operating at typical maximum duty) would be as follows:

Guest bedrooms – NR 25 dB at 1.5m from any ventilation aperture;

Staff/meeting/training rooms – Between NR 30-40 dB at 1.5m from any ventilation

aperture

4.18 The MVHR system will also need to be specified to ensure that sufficient ventilation rates can be

provided with windows closed to prevent units overheating in summer months.



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4.19 Calculations were carried out using façade modelling software in accordance with the “more

rigorous” methodology given in BS8233 to calculate the sound insulation performance required of

the glazing and ventilation to achieve the nominated internal noise criteria in the ‘worst-case’

habitable rooms of the development (i.e. the habitable rooms that will be subject to the highest

external noise levels).

4.20 If acceptable internal noise levels can be achieved in ‘worst case’ habitable rooms then it follows

that acceptable internal noise levels can be achieved in all other habitable rooms of the

development using similar glazing and ventilator types.

4.21 The calculations were carried out for two ‘worst case’ scenarios. The first scenario is based on the

typical known dimensions/details for facade elements within habitable rooms of the proposed

residential dwellings. The second scenario is based on the typical known dimensions/details for

façade elements within habitable rooms of the proposed hotel.

Scenario 1

Glazing – 2.5m2 for bedrooms and 6m2 for living rooms;

External walls – 3.7m2 for bedrooms and 4.6m2 for living rooms; and

2 in-frame trickle ventilators in bedrooms and 3 in-frame trickle ventilators in living rooms.

Scenario 2

Glazing – 2.5m2 for bedrooms and 6m2 for living rooms;

External walls – 3.7m2 for bedrooms and 4.6m2 for living rooms; and

4.22 The results of the calculations are shown in Appendix 5 and are summarised in Tables 2 and 3.

Table 2 Acoustic Requirements for ‘Worst Case’ Habitable Rooms within Residential Dwellings

‘Worst Case’ Rooms Glazing Performance

Requirements (inc. Frames)

Ventilator Performance

Requirements

Bedrooms facing West Green

Road façade

(2300-0700hrs)

37 dB Rw+Ctr 44 dB Dne,w + Ctr

Living rooms facing West Green

Road façade

(0700-2300hrs)

37 dB Rw+Ctr 44 dB Dne,w + Ctr

Note The requirements given are approximate only and should be confirmed at the

detailed design stage when full design details are available.



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Table 3 Acoustic Requirements for ‘Worst Case’ Guest Bedrooms within Hotel

‘Worst Case’ Rooms Glazing Performance Requirements (inc. Frames)

Bedrooms facing West Green Road façade

(2300-0700hrs)

33 dB Rw+Ctr

Note The requirements given are approximate only and should be confirmed at the detailed

design stage when full design details are available.

4.24 The required sound insulation performance values in Tables 2 and 3 could typically be achieved

by the glazing and ventilator types shown in Table 4.

Table 4 Typical Glazing / Ventilator Acoustic Performances

Glazing (in Good Quality Sealed Frames) Typical Weighted Sound Reduction

(Rw + Ctr)

8.8mm/16/4mm acoustically upgraded thermal double glazing 33

10mm/16/8.8mm acoustically upgraded thermal double glazing 37

Ventilators Typical Acoustic Performance

(Dnew + Ctr)

Greenwood AAB4000 through wall acoustic ventilator 44

Greenwood Airvac MA3051 through wall acoustic ventilator 52

4.25 It can be seen from the above that acceptable internal noise levels will be achievable in the

development, subject to the specification of suitable glazing and ventilation systems at the detailed

design stage (which could be secured with a suitable planning condition). It is our view therefore

that the proposed development is, in principle, acceptable with regards to the noise levels that will

exist within the habitable rooms.

4.26 It should be noted that it will be possible to use lower acoustic performance façade elements for

façades that are further from or acoustically screened from the surrounding noise sources. This

could be investigated further at the detailed design stage.



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Noise levels in external amenity areas

4.27 The layout of the development has also been reviewed in relation to the BS8233 recommendation

that noise levels in external amenity areas should ideally not exceed 50 – 55 dB LAeq,T.

4.28 Based on the results of the environmental noise survey, noise levels on balconies on the façades

directly overlooking West Green Road and Ifield Road would be expected to exceed the BS8233

recommended levels by approximately 9-17 dBA depending on height and aspect. However, whilst

this is not ideal, in our view, exceeding the BS8233 recommended levels does not normally mean

that the balconies would be unacceptable to future residents. The reasons for this are as follows:

Most developments in urban areas will be subject to noise levels above the BS8233

recommended levels for balconies1.

It is common for noise levels on balconies facing main roads to exceed the BS8233

recommended noise levels in Crawley and elsewhere;

It is reasonable to assume that residents would prefer the option to have a noisier balcony

as opposed to having no balcony at all;

In this case all residents will have the use of the ground floor level communal amenity

areas between the blocks where the predicted noise levels are lower than the BS8233

‘desirable’ levels;

The balconies will have glass balustrades, which will reduce the road traffic noise levels

on the balconies as far as is practicable. There are no other noise mitigation measures

available for balconies other than fully enclosing them (‘winter gardens), which essentially

changes the balconies into internal rooms; and,

Planners often consider it to be beneficial to the street-scape to have balconies facing

roads as they help marry the development to the surrounding area.

The current design of the development is therefore considered to be acceptable in relation to noise levels

in external amenity areas.

1 Table 2 from BS8233 notes that daytime noise levels will typically exceed 50-55 dB LAeq,16hr in areas close to busy main

roads. It was also found in the UK National Noise Incidence Study 2000/2001 that 90% of UK homes were exposed to daytime

noise levels >50dB LAeq,16hr and 54% of UK homes were exposed to noise >55dB LAeq,16hr. It is reasonable to assume that

a high percentage of these were in urban areas.



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5. PLANT NOISE IMPACT ASSESSMENT

5.1 It will be important to ensure that noise emissions from external mechanical plant associated with

the development will not disturb either nearby existing noise sensitive receptors, or future noise

sensitive receptors associated with the development itself.

Design criteria – Mechanical plant noise

5.2 BS4142:2014 – Methods for rating and assessing industrial and commercial sound (BS4142) can

be used to assess the impact of a new industrial and/or commercial noise source(s) on nearby

sensitive receptors.

5.3 The BS4142 assessment methodology can be summarised as follows:

1. Measure the existing background noise levels (LA90,T dB) at the locations of nearby

noise sensitive receptors during the quietest periods when the noise source(s) under

investigation will operate;

2. Predict or measure the noise emissions (LAeq,T dB) from the noise source(s) under

investigation at the location(s) of the nearby sensitive receptors, including corrections for

any distinguishable acoustic features (e.g. tones, whines, screeches, hisses etc);

3. Subtract the measured background noise levels (item 1 above) with the measured or

predicted rating noise levels (item 2 above) at each sensitive receptor. BS4142 states

that:

a) Typically, the greater this difference, the greater the magnitude of the impact.

b) A difference of around +10 dB or more is likely to be an indication of a significant

adverse impact, depending on the context.

c) A difference of around +5 dB is likely to be an indication of an adverse impact,

depending on the context.

d) 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.

NOTE Adverse impacts include, but are not limited to, annoyance and sleep disturbance.

Not all adverse impacts will lead to complaints and not every complaint is proof of an

adverse impact.

5.4 CBC’s planning policy requires that all new fixed plant and machinery is designed to achieve a

rating level at least 10 dB below the existing background noise level at surrounding sensitive

receptors.

5.5 Typical background noise levels (LA90) at the site were measured as part of the site noise survey

outlined in Appendix 3. The measured background noise levels have been used to develop limits

for plant noise emissions from the new development at the positions of the surrounding residential

properties in accordance with the BS4142 assessment methodology. The limits are shown in Table

5.



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Table 5 BS4142 Noise Limits - Free-field Levels

Location Period

Day-time/Evening (0700-

2300hrs)

Night-time (2300-0700hrs)

Nearest residential properties to

proposed development (approximately

25m

45 dB LAeq 27 dB LAeq

Note 1 The above limits assume that the fixed plant will not have any distinctive acoustic features (e.g. tones,

impulses, intermittency etc)

Proposed mechanical plant design

5.6 Detailed design information is not yet available for external mechanical plant for the development,

and therefore noise emissions from external mechanical plant cannot be accurately predicted at

the positions of nearby residential properties at this stage.

5.7 It is expected that it will be straightforward to achieve the BS4142 daytime noise limits given the

high background noise levels. However, mitigation measures (i.e. a suitable acoustic enclosure,

equipment with a lower noise emission ‘night mode’ etc.) may need to be incorporated into the

design in order to achieve the night-time limits for mechanical fixed plant.

5.8 The selection and design of external mechanical plant will be reviewed as information becomes

available to ensure that the project BS4142 noise limits given in Table 5 are achieved. Compliance

with the limits could be secured through the imposition of a suitable planning condition if deemed

necessary by the Local Planning Authority.



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6. NOISE BREAKOUT FROM THE HOTEL PLANT ROOM

6.1 It is noted that there is a plant room on the ground floor of the proposed hotel with guest bedrooms

located on the floor above.

6.2 Noise and vibration emissions associated with the plant room cannot be fully assessed until full

details of proposed plant are known. However, it is generally straightforward to control noise and

vibration within plant rooms using the following noise mitigation measures:

Designing high acoustic performance separating walls and floors between the plant room

and the residential units above; and,

Isolating any sources of vibration with appropriate anti-vibration mounts to minimise

structure borne noise and vibration.

6.3 The above measures can be investigated further at the detailed design stage and this could also

be secured through the imposition of a suitable planning condition if deemed necessary by the

Local Planning Authority.



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7. CONCLUSIONS

7.1 Cass Allen Associates was instructed by Sloane Crawley Properties Ltd assess the suitability of

the site for the proposed development with regards to noise.

7.2 The assessment was carried out in accordance with relevant local and national planning guidance.

7.3 A noise survey was carried out at the site between 18th and 19th November 2014. Noise levels

across the site were generally dictated by road traffic sources on West Green Drive and Ifield Road.

7.4 Acceptable internal noise levels are predicted to be achieved inside the worst-case habitable rooms

of the flats within the development subject to the adoption of commercially available acoustically

upgraded glazing and ventilation in the development design.

7.5 Based on the results of the environmental noise survey, noise levels on balconies on the façades

directly overlooking West Green Road and Ifield Road would be expected to exceed the BS8233

suggested levels. However, whilst this is clearly not ideal, BS8233 recognises that where

exceedances are found, the development should be designed to achieve the lowest practicable

noise levels in external amenity spaces. This has been taken into consideration in the assessment.

7.6 Appropriate limits for noise from mechanical plant have been calculated based on measured typical

noise levels at the site and guidance given in BS4142. It is envisaged that it will be straightforward

to achieve the plant noise limits, subject to the specification of mechanical plant and mitigation

measures (if required) at the detailed design stage.

7.7 Noise breakout from the proposed hotel plant room cannot be fully assessed until full details of the

proposed plant are known. However, it is generally straightforward to control noise and vibration

emissions within plant rooms, subject to the incorporation of suitable mitigation measures (if

required) at the detailed design stage.

7.8 In summary of the above it is our view that the site is suitable for the development in terms of noise.

Glossary

Term Explanation

Noise

Sound that is unpleasant or that causes (or could cause) disturbance or annoyance. Noise is

assessed in terms of sound pressure levels.

dB (decibel) The standard unit for defining sound pressure levels. The lower threshold of normal hearing is in the

region of 0dB. 130dB is the upper threshold of pain.

A change of 1dB in sound pressure levels is only perceptible under controlled conditions. The

minimum perceptible change under normal conditions is 3dB. A change of 5dB would be clearly

noticeable to the average listener. A change of 10dB roughly corresponds to a subjective ‘halving’ or

‘doubling’ of loudness.

The decibel is a logarithmic quantity, meaning the normal arithmetic rules of mathematics cannot be

directly applied. For example:

30dB + 30dB ≈ 33dB;

3 x 20dB ≈ 25dB, and;

40dB – 25dB ≈ 40dB

dBA (A-weighted

decibel)

A-weighted decibels have been corrected

using a frequency weighting (A-weighting) that

broadly corresponds with the hearing

response of the human ear. Measurements of

noise in dBA are generally used for assessing

people’s perception of noise.

The table on the right shows indicative A-

weighted noise levels (sound pressure levels)

from a variety of sources.

Source, distance Level (dBA)

Jet aircraft, 50m away 140

Threshold of pain 130

Threshold of discomfort 120

Chainsaw, 1m distance 110

Disco, 1m from speaker 100

Diesel truck, 10m away 90

Kerbside of busy road, 5m 80

Vacuum cleaner, distance 1m 70

Conversational speech, 1m 60

Average home 50

Quiet library 40

Quiet bedroom at night 30

Background in TV studio 20

Rustling leaves in the distance 10

Threshold of human hearing 0

LAeq,T (equivalent

continuous noise level)

The sound level of a notionally steady sound having the same energy as the A-weighted fluctuating

sound over the measurement period (T). The A-weighted equivalent continuous noise level (LAeq) is

commonly used to describe the “average” or “ambient” noise level in a given environment over the

measurement period.

LA10,T The A-weighted level of noise exceeded for 10% of the specified measurement period (T). It gives an

indication of the upper limit of fluctuating noise and is commonly used to describe road traffic noise

levels. LA10,18h is the arithmetic average of the 18 hourly LA10,1h values from 06.00 to 24.00 (defined

in CRTN).

LA90,T The A weighted noise level exceeded for 90% of the specified measurement period (T). It is

commonly used to define “background” noise level, i.e. the underlying noise level in the absence of

intermittent or short-duration noises.

Term Explanation

LAmax (maximum noise

level)

The highest A-weighted noise level recorded during the measurement period. Unless described

otherwise, it is generally measured using the ‘fast’ sound level meter response.

Hz (Hertz) Hz are the unit of frequency, equal to one cycle per second. Frequency of sound waves refers to the

number of pressure fluctuations per second. Frequency is related to the pitch of a sound.

Octave-band or

third-octave

band (1/1 or 1/3)

The spectrum of audible frequencies can be separated into proportional ‘bands’ to facilitate ease of

computation and analysis (the bandwidth being proportional to the band centre-frequency). Third-

octave bands (1/3-octave) split each octave into 3 bands, which allows greater accuracy.

Free-field A sound field determined at a point away from reflective surfaces other than ground with no significant

contributions due to sound from other reflective surfaces. Generally as measured outside and away

from buildings.

Facade-level A measurement taken in close proximity (e.g. 1m) to a reflective surface (other than ground) such as

a building facade. It is generally accepted that reflections from the surface will increase the measured

noise levels by around 3 dB compared to free-field levels, i.e. free-field levels = facade levels – 3 dB.

Reverberation The sound in a room or enclosed space that results from reflections from the room boundaries. The

reverberation time (RT) is the time required for the steady sound pressure level in an enclosed space

to decay by 60dB.

Sound absorption The process whereby sound energy is converted into heat, leading to a reduction in the sound

pressure level. Directly related to reverberation in an enclosed space, i.e. more absorption = lower

reverberant level and shorter reverberation time.

Sound insulation A general term referring to the degree by which a material or separating construction reduces sound

energy passing through it.

Dw (weighted sound level

difference)

Describes the weighted sound level difference between a source room and receiving room when

noise is being generated in the source room. Used to assess and describe the sound insulation

between the two rooms. DnTw is the sound level difference normalised to a reference reverberation

time (0.5 seconds unless stated otherwise).

Lw (weighted sound level

difference)

Describes the weighted impact sound insulation of a floor. Impact sound is sound caused by physical

impacts (such as footfall) on the floor. Impact sound insulation is quantified by placing a ‘tapping

machine’ on top of the floor and measuring the resultant noise levels in rooms below. LnTw is the

sound level difference normalised to a reference reverberation time (0.5 seconds unless stated

otherwise).

Rw (Weighted sound

reduction index)

The weighted sound reduction index (see SRI entry below) is a single number laboratory-measured

rating used to describe the sound insulation performance of building elements. The R’w is the

apparent sound reduction index measured onsite (normally tends to lower than the laboratory rated

Rw level due to onsite conditions).

SRI (Sound Reduction

Index)

A laboratory-measured rating of the airborne sound insulation properties of building elements across

various frequencies.

NR (Noise Rating) Noise rating is a method for assigning a single number level to a noise spectrum. It is typically used

to specify allowable noise emissions from mechanical ventilation systems in buildings. For a typical

noise spectrum the NR level is approximately equivalent to the dBA level minus 6, i.e. NR ≈ dBA –

6.

Current Development Drawings

Survey Results

Survey Summary: The survey comprised short-term operator attended noise measurements and longer-term

unattended noise monitoring at the site. Noise levels at the site were generally dictated by road traffic

on surrounding roads. Vibration levels at the site were very low.

Survey

Period:

18/11/2014 to 19/11/2014

Survey Objectives:

To identify noise sources that contribute to ambient noise levels at the site;

To measure noise levels around the site over a typical day and night-time period.

Equipment Used: Type Manufacturer Model Serial Number

Sound level meter1 Bruel & Kjaer 2250 2630237

Calibrator Bruel & Kjaer 4231 2115551

Sound level meter1

(noise logger)

Rion NL-32 00530374

Sound level meter1

(noise logger)

Rion NL-32 01182950

Note 1: All sound level meters were calibrated before and after measurement periods and no significant drift in calibration was found to have occurred. The results of the measurements are therefore considered to be representative.

Weather Conditions: The observed weather conditions were acceptable for acoustic measurement throughout the

attended survey periods (low-medium wind speeds and no rain). Weather records for the area

confirmed that weather conditions were also generally acceptable for acoustic measurement during

the unattended monitoring.

Measurement

Positions:

Position (refer plan below)

Description

N1 Attended noise monitoring position. 1.5m above local ground level. Free-field. Direct line of sight to West Green Road.

L1 Unattended noise logging position. Approximately 3.5m above local ground level. Free-field. Direct line of sight to West Green Road.

L2 Unattended noise logging position. Approximately 3.5m above local ground level. Free-field. Direct line of sight to West Green Road.

Site Plan showing

Measurement

Positions:

Attended Noise

Monitoring Results:

Date Position Time Meas.

Length

LAeq,

dB

LAmax,

dB

LA90,

dB

Observations

18.11.14 N1 15:25 9 secs - 79 - Maximum noise measurement of bus passby on

West Green Road

15:29 7 secs - 78 - Maximum noise measurement of bus passby on

West Green Road


West Green Road


West Green Road

15:22 5 secs - 75 - Maximum noise measurement of car passby on

West Green Road


West Green Road


West Green Road


West Green Road


West Green Road

15:22 5 secs - 78 - Maximum noise measurement of van passby on

West Green Road

N1

L1

Site

L2

Unattended Noise

Monitoring Summary:

Meas. Period Position Daytime (0700-2300hrs) Night-time (2300-0700hrs)

LAeq,16hr,

dB

LA90,1hr dB1 LAeq,8hr,

dB

LA90,5mins,

dB1

LAmax, dB2

18.11.14 to 19.11.14 L1 67 55 58 37 80

18.11.14 to 19.11.14 L2 64 55 57 47 75

Note 1: Most frequent typical background noise level measured during the period shown.

Note 2: Highest typical maximum noise level during the night-time (not exceeded more than 10-15 times per night).

Unattended Noise

Monitoring Graphs:

Meas. Period Position

18.11.14 to 19.11.14 L1

Meas. Period Position

18.11.14 to 19.11.14 L2

CAA Noise Contours for a 2 Runway Future Scenario at London Gatwick Airport

Site

FACSIM Calculations

www.cassallen.co.uk

Documents

RP01-14545 - Sloane Crawley Properties Ltd - Ifield Road ... · 1.1 Cass Allen Associates has been instructed by Sloane Crawley Properties Ltd to assess the suitability of the site