defra wt1505

DEFRA WT1505 Foul Drainage Report 28/03/2013 Revised: 19 April 2013

Confidentiality: Public

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Project number: 50600471 Dated: 28/03/2013 2 Revised: 19 April 2013

Quality Management

Issue/revision Issue 1 Revision 1 Revision 2 Revision 3

Remarks Final Final Final

Date 28th March 2013 11th April 23 April

Prepared by Steve Wilson – EPG Nick Orman - WRc Alastair Atkinson - WSP

Steve Wilson – EPG Nick Orman - WRc Alastair Atkinson - WSP

Steve Wilson – EPG Nick Orman - WRc Alastair Atkinson - WSP

Signature

Checked by A L Atkinson A L Atkinson A L Atkinson

Signature

Authorised by C J Tyler C J Tyler C J Tyler

Signature

Project number 50600471 50600471 50600471

Report number 2 2 2

File reference n:\50600471 - defra - wt1505 evidence costs\c documents\reports\foul drainage report\foul drainage report final - 24-4-13.docx

n:\50600471 - defra - wt1505 evidence costs\c documents\reports\foul drainage report\foul drainage report final - 24-4-13.docx

n:\50600471 - defra - wt1505 evidence costs\c documents\reports\foul drainage report\foul drainage report final - 24-4-13.docx

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DEFRA WT1505

Foul Drainage Report

28/03/2013

Client DEFRA Nobel House 17 Smith Square London SW1P 3JR

Consultant WSP UK Ltd Mountbatten House Basing View Basingstoke RG21 4HJ UK Tel: +44 (0)1256 318800 Fax: +44 (0)1256 318700 www.wspgroup.co.uk

Registered Address WSP UK Limited 1383511 WSP House, 70 Chancery Lane, London, WC2A 1AF

WSP Contacts Chris Tyler Alastair Atkinson



Table of Contents

1 Introduction ............................................................................ 5

2 Foul Drainage - Design Approach ......................................... 7

3 Capital Cost Assessment ....................................................... 9

4 Additional Operational and Maintenance Costs ................... 15

5 Summary and Discussion of Key Issues.............................. 18 Appendices

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1 Introduction

1.1 Report Content and Structure 1.1.1 This report forms one of the deliverables for the WT1505 project ‘Evidence on the costs of 1) New

Build Sewers under different conditions and standards and 2) increasing the uptake of sustainable drainage systems in New Developments.

1.1.2 The report assesses the cost differential associated with the implementation of the Draft Secretary of State’s National Standards April 2013 (Draft National Standard) compared to Part H of the Building Regulations 2002 (B Regs). To assess the costs of implementation of these standards the report assesses foul drainage designs for three different scale sites; small, medium and large. Designs have been produced firstly; to comply with the Draft National Standard and secondly to comply with the current Part H of the Building Regulation 2002.

1.1.3 There have been a number of changes to standards and approaches within the water industry from when Part H of the Building Regulations was published in 2002 to April 2013. The approach recommended by Sewers for Adoption has changed several times with the most recent version being the 7th edition. The previous 6th Edition (2006) included the adoption of laterals and the introduction of demarcation chambers.

1.1.4 The capital and maintenance costs for each scheme have been identified.

1.2 Site Selection 1.2.1 Three sites have been selected to be suitable for testing both the foul and surface water designs and

standards. The sites were selected on the following criteria; to reflect scales and type of development which the industry delivers across the country, layouts which could be enhanced to be fully SUDS compliant and schemes either under construction or have been built.

1.2.2 The small site was selected as being representative of a small 4-8 unit infill development. It should be noted that the site could have been split into two separate areas but for the purpose of the review was left as one site of 8 units. These units have a range in size to reflect slightly larger housing. The plot is part of a larger development layout and is currently under construction.

1.2.3 The medium site layout was selected as being a typical size for a development parcel and provides 33 houses. It is an actual development parcel taken from a larger site. The medium site utilises layouts widely used in the industry and contains smaller houses and gardens than the small site but the style of the development is one with housing fronting onto the road and courtyard parking behind.

1.2.4 The large site provides an example of a large development (210 dwellings) containing both flats and houses. The site is split into a number of development blocks surrounding courtyard parking areas. Between these development blocks are the connecting highway and strategic swales.

1.2.5 Whilst the sites are representative of the type and nature of development the industry has been delivering, the development layouts and associated drainage design will reflect local conditions and individual developer practices and drivers.



1.3 Housing Developer Strategies 1.3.1 There are many policies and market drivers which influence the design of drainage layouts. One such

issue is the proximity of the house frontage to the footway and size or absence of front gardens. There are issues such as frontage vehicle access and on plot frontage parking /garages versus rear mews and parking courts. There are behavioural issues which influence marketability of houses such as perceived reluctance to use rear parking thus causing obstructions to the access roads. All these issues mean that house layouts and thus drainage layouts vary to reflect planning authority priorities and housing developer marketability requirements.

1.3.2 Another significant issue is the phasing of medium to large scale developments. For various reasons some developers secure full consent for the primary road and sewer network prior to the detailed consent for the housing layout. This allows them to deliver the primary infrastructure early. This has the advantage that new occupiers benefit from a completed road access and do not have to drive through a live building site. However the disadvantage is that the precise position of drainage connections from houses are unknown when the main sewers in the roads are constructed and thus stub connections for laterals cannot be provided. Retrofitting laterals and connections to the sewer (“saddles”) causes significant disruption and reinstatement cost. Consequently it is then advantageous to run the drainage through rear gardens. The alternative is to move the houses back from the footway to create adequately deep front gardens to accommodate “carrier” drains.

1.3.3 The costing exercise contained in the report look at built development layouts and therefore the implications of layout are not a direct parameter tested in this report.

1.3.4 The housing layouts selected are based on real schemes which have been built relatively recently but the drainage layouts modified to comply more fully than the approved constructed layouts.

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2 Foul Drainage - Design Approach

2.1 Background 2.1.1 The design approach for this element of work has been progressed as if it was a scheme to be

constructed by a developer. Therefore the generated strategies should reflect the future design produced by the industry. The table below contains the design criteria.

Topic Building Regulations Draft Secretary of State’s Standards

Flow Rates Generated using the discharge unit method which generates a higher discharge rate.

Generated using 4000 l / property / day

Self -Cleansing Velocity We have achieved the self-cleansing velocity of 0.75 m/sec or we have used deemed to satisfy minimum gradients for pipes.

We have achieved the self-cleansing velocity of 0.75 m/sec or we have used deemed to satisfy minimum gradients for pipes.

Outfall Location We have only used positive drainage with connections to assumed existing adjacent public sewers

We have only used positive drainage with connections to assumed existing adjacent public sewers

Pumping Station No pumping stations are required No pumping stations are required

All Connection Points from the Buildings are Assumed to be SVP

No ventilation is provided on the main runs No ventilation is provided on the main runs

Depth of Drains All drains in mews / hardstanding areas have been designed to be sufficiently deep and with appropriate pipe bedding to accommodate vehicle loads.

All drains in mews / hardstanding areas have been designed to be sufficiently deep and with appropriate pipe bedding to accommodate vehicle loads.

Access to Runs It is assumed that mews access to private parking areas are accessible 24 hours a day

It is assumed that mews access to private parking areas are accessible 24 hours a day

2.1.2 Within the housing industry there are two different approaches to the layout of connecting drains from internal down pipes to the external drains. One approach is to minimise the amount of external drainage by running connections under the floor slab, the other is to minimise the length of pipework under the slab by taking pipes to the nearest external point and route drains around the external perimeter. The former policy may make repairs under the slab more difficult whereas the latter involves more external pipes and chambers which is less attractive to prospective house purchasers.

2.1.3 There are pros and cons with each approach and different developers have different preferences. For this study the drainage layouts utilise the drainage which runs under the house. However, as this study is designed to compare the costs between the two standards rather than provide a definitive approach the difference in cost is deemed to be neutral.

2.1.4 For the large scheme the properties drain to the rear of the properties and through the courtyard parking / mews areas as this would provide the accessible areas which are deemed to be suitable access to maintain the drainage.

2.1.5 There is an alternative approach where the properties drain to the front of the property to a sewer located within front gardens or the highway corridor. The location of the sewer in the front of the properties also has a number of pros and cons which partly relate to the drainage issues and partly to wider master planning and layout trends both of which are likely to change with over time.

2.1.6 Draining to the front of the properties would result in less duplication of pipework and therefore could have a reduction in the costs as long as the drainage is built at the same time as the highway. However, if the highway and the sewer is constructed first and the houses come along at a later point in time it could require a number of additional connections on the sewer. This will generate additional costs associated with making the connections and the reinstatement of the highway.



2.1.7 The proposed approach undertaken by developers is likely to depend on the requirements of individual sites and the preferences of developers and how the industry evolves to maximise the benefits of the new standards and minimise the requirement to deliver the intent of the current Building Regulations.

2.1.8 Therefore, the drainage strategies costed, reflect how they could be achieved using historical and current housing layouts so the costs can be compared against a current practice.

2.1.9 The table below sets out the length of sewers for each scheme (excluding some of the connections to chambers from the SPV),and has been included to assess the likely additional lengths of adoptable drainage in the schemes rather than definitive lengths.

Sites Total Pipe Length Adopted Pipe Length

Small Site

Building Regs 97.5m* 0.0m

Draft National Standard Layout

98.5m* 83.5m

Medium Site



625.0m* 548.0m

Large Site



2988.5m* 2389.0m

Large Site (alt)


2449.5m 2298m

* Ignores the length of pipe between SVP and First Chambers

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3 Capital Cost Assessment

3.1 Background 3.1.1 The capital costs have been calculated for the compliant schemes designed in accordance with the

Building Regulations and Draft Secretary of State’s Standards April 2013.

3.1.2 There are a number of elements which affect the cost, the design layouts and associated implications which essentially relate to two main issues;

1) The Draft National Standard are seeking that the original intent of Building Regulations is delivered rather than the current layouts which are currently deemed to be compliant,

2) The Sewers for Adoption 7th Edition recommends the use of demarcation chambers which has not been historically used in the Building Regulations design.

3.2 Compliance with Building Regulations 3.2.1 The guidance in support of Requirement H1 of the Building Regulations has, since 2002, stated that:

"In the Secretary of State's view the requirement of H1 will be met if a foul water drainage system:

…

e) is accessible for clearing blockages;"

3.2.2 and that paragraph 2.51 of approved document H1 states:

"Access points to sewers (serving more than one property) should be in places where they are accessible and apparent for use in an emergency. Examples of suitable locations include, highways, public open space, unfenced front gardens, and shared or unfenced driveways."

3.2.3 Even as far back as SfA 6th para 2.4 says Manholes should be accessible 24 hours a day, however it does not specifically say that the minor inspection chambers must be accessible. Notwithstanding these requirements it is apparent that access points on sewers are still commonly located in enclosed rear gardens where they are not readily accessible for use in an emergency. Therefore, the industry have developed an acceptable approach which is deemed compliant although not in line with the original intent of the Building Regulations. This report assumes that tested layouts defines an acceptable layout to reflect the current approach of the industry. There is a similar requirement in the proposed Secretary of State's standards to that set out above and therefore this has been considered as if it were a new regulatory requirement, but we have identified the costs separately.

3.3 Compliance with Sewers for Adoption 3.3.1 Both editions of Sewers for Adoption (6th & 7th Editions) recommend the use of demarcation

chambers, the requirement of the Draft National Standards are reflected in SFA. This reflects the changes to Section 104 of the Water Industry Act 1991 that were introduced by the Water Act 2003. The costs of installing the demarcation chambers has been picked up in the cost deferential between the two scenarios but the cost have been identified separately as these costs are associated with these earlier changes rather than the Draft National Standards.

3.3.2 There is a presumption in Sewers for Adoption 6th Edition (Part 2c – Lateral Drains para 2.23.4) that private drains and laterals will be in front gardens and powers under S158 or 159 of the Water Industry Act 1991 will enable access.



3.4 New standards 3.4.1 The industry recommendations in support of the draft Draft National Standard make reference to BS

EN 13598 for plastic inspection chambers as this has superseded BS 7158 which has been withdrawn by BSI. Approved Document H still makes reference to BS 7158, but in the ordinary course of events will be updated with the new standard at the next revision. It is understood that Water and Sewerage Companies are prepared to accept chambers complying with the requirement of BS 7158 as long as they are still available. It is not therefore clear whether any additional costs associated with this change should be included

3.4.2 The assumptions used are set out below along with the summary of the cost. The more detailed breakdowns are included in the appendices.

3.5 General approach

Capital costs 3.5.1 The difference in capital costs has been determined for two different foul sewer layouts in each site as

follows:

Layout and construction compliant with the current Building Regulations;

Layout and construction compliant with Draft Secretary of State’s Standards April 2013 (Draft National Standard).

3.5.2 The capital cost estimates have been produced with the aim of providing an estimate of the difference in cost between schemes designed to the different standards. The cost estimates for individual layouts should not therefore be considered absolute values because items that will not have any significant bearing on the cost difference have not been included (for example pipe bends and connections, internal connections, minor technical detail variations).

3.5.3 The sewers and laterals have been designed using the Micro Drainage suite of software (Windes). This software designs the pipe networks undertakes hydraulic analysis and produces pipe and manhole schedules.

3.5.4 The main quantities for the manholes and pipe runs have been taken off the output schedules for the system on the Micro Drainage model sheets. The main items are manholes, inspection chambers, access chambers and pipes. The following assumptions have been made regarding the main materials regardless of code applied:

All main sewer runs below adopted highway are in vitrified clay with DOT Type 1 stone trench backfill.

All manholes in adopted highways are pre-cast concrete construction;

All sewers and laterals below shared access or mews areas are in uPVC but use DOT Type 1 stone trench backfill

All sewers and laterals below other areas including gardens, etc are in uPVC with as dug trench backfill.

All sewers, drains and laterals will have type “s” single size pipe bedding and surround

All manholes/inspection chambers below other areas are plastic construction with DOT Type 1 stone surround based on SfA 7th details

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3.5.5 The costs for the main items have been taken from SPONS Price Books, 2013. The main books that have been used are the Civil Engineering and Highway Works Price Book and the External Works and Landscape Price Book.

3.5.6 Often drainage is let as part of a wider groundworks package and therefore preliminaries specific to the drainage element are very difficult to estimate. They are therefore not included and are not considered likely to make a huge difference to the cost variations that have been identified.

Design costs 3.5.7 The design of the different systems is not likely to result in any significant increase in design costs.

3.6 Results – capital costs 3.6.1 The cost difference for the foul sewers for the small and medium sites has been estimated and the

results are summarised in Table 1 together with the differences in the main quantities in Table 2.

Table 1

Small Medium large Current Interpretation of Building Regulations

£28,630 £82,973 £326,129

Secretary of State Standards (SOS) inc demarcation chambers recommended by SFA 7

£29,236 £83,865 £378,399

Difference £606 £892 £52,270 Cost of demarcation Chambers recommended by SFA 7 and not an additional requirement of the Draft National Standards

£827 £3,314 £34,791

Cost difference associated with providing accessibility to the sewers as part of SFA7 and not a new recommendation of the Draft National Standards

None Nominal £17,479

No of properties 8 33 210 Costs per property associated with the delivery of the Draft National Standard but ignoring the SFA7 requirements

-£28 -£73 £0



Key quantities Small Medium Large Manholes (No) Current Interpretation of Building Regulations

5 15 41

Draft National Standard

5 7 33

Inspection chambers (No) Current Interpretation of Building Regulations

12 39 204


16 51 312

Extra demarcation chambers required by SFA 7 and Draft National Standard

2 8 84

Pipes – total length (m) Current Interpretation of Building Regulations

283* 630 2614


280* 625 (+10m additional

under slab)

2987

*This includes the pipe connections between SPV and First Chamber

3.6.2 The analysis has shown that there is a cost differential between the current industry approach to the implementation of the B Reg 2002 and the proposed Draft National Standard. This amount ranges from £27-£249 per property. However, these costs were aggregated from a number of elements rather than the costs being a direct result of the proposed Draft National Standard.

3.6.3 The analysis identified that this cost differential is generated by three factors

1. The proposed Draft National Standard requires the original intent of the B. Regs to be implemented rather the current approach to accessibility which does not provide genuine 24 hour access but is deemed to comply.

2. The requirement of demarcation chambers as defined in SFA7 is a cost already been incorporated within the current industry approach.

3. The cost of providing accessible drainage within the parking courtyard as defined in Sewers for Adoption and therefore is a cost already been incorporated into the current industry approach

3.6.4 For the large site it is clear that delivering the requirements for extra accessibility leads to an increased cost, this increase is primarily a factor of the courtyard layout and the requirement to move the private drainage away from the building to a publicly accessible area. However, there are no additional costs associated with a scheme designed to adoptable standards.

3.6.5 The large site required an additional 373m of sewer. These are required to provide accessible sewerage within the parking areas. This accessibility required additional lengths of sewers and longer adoptable sewerage connections from a demarcation chamber to the collateral sewer. This sewer was located in a trafficked area rather than in a garden and therefore the sewerage would need additional bedding and surround.

3.6.6 When the differential costs were reviewed removing the costs associated with the demarcation chambers, the cost differential changes to a range of -£73 to + £83.

3.6.7 When the costs for the Draft National Standard scheme are compared to the industry recommendations to deliver for SFA7 then there are no additional costs anticipated.

3.6.8 The drainage for any site needs to fit around the housing layout and the individual site requirements therefore the design needs to reflect the layout which depend on a number of factors. The costs identified above resulted in accessible seeking to drain into the private courtyards to the rear of the properties which leads to duplication of drainage. Therefore, some of the cost increase is a function of the layout as well as the standards.

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3.6.9 An alternative system was developed and costs draining directly to the front of the properties the costs are further reduced as a result of a reduction in pipe length and a number of extra chambers required. The details of this are detailed in the table below.

Table of Costs with Alt Draft National Standard

Large Large (alternative)

Current Interpretation of Building Regulations £326,129 £326,129

Secretary of State Standards (SOS) inc demarcation chambers recommended by SFA 7

£378,399 £260,708

Difference £52,270 -£65,421

Cost of demarcation Chambers recommended by SFA 7 and not as a result of the Draft National Standard

£34,791 £2,070

Cost difference associated with Draft National Standard and the current interpretation of Building Regulations

£17,479 -£63,351

No of properties 210 210

Costs per property etc as before £83 -£302

Key Qualities

Large Large (alternative)

Manholes (No)

Current Interpretation of Building Regulations 41 41

Draft National Standard 33 32

Inspection chambers (No)



Extra demarcation chambers recommended by SFA 7 and Draft National Standard

84 5

Pipes – total length (m)



3.6.10 This alternative scheme has not been used as part of the comparison in Table 1 as it was felt it would not be a direct comparison as a result on the new standards, additionally the cost assumes that the houses and roads are constructed together. However, it does show it is possible to design more effectively reducing the additional number of demarcation chambers required only to act as demarcation chambers and that the length of pipework could be reduced.



3.6.11 It is known that draining to the front of properties does not always fit into the phasing current delivered by the industry and therefore using current practices these additional savings may not be fully realised. There is likely to be an additional costs associated with retrospectively connecting onto the sewers built as part of an infrastructure phase these will include (reinstatement of highways and saddle connections to sewers). The number of additional connections will depend on the phasing of the layout and construction. Therefore the findings have been left in the report although not part of the key findings.

3.7 Disposal of Arising 3.7.1 The presence of contaminated soil could in theory have a large influence on drainage costs.

However given the minimal variation in the main quantities of pipes and manholes/chambers due to the different standards this is not believed to be significant. In any event most developers and earth works contractors will seek to minimise expensive disposal of clean material offsite. A major remediation contractor has been consulted regarding contaminated soil disposal from sites. Material which is deemed ‘clean’ has until now been taken from developments to exempt disposal sites. However, these exemptions have generally been withdrawn (there is a transition period whereby existing exempt sites have until sometime in late 2013 to finish). Therefore, no new exempt sites will be available for spoil disposal off-site (there are still some new exemptions available, but they all generally not applicable for large scale earthworks). Most areas still have access to existing exempt sites meaning there is no real change at the moment.

3.7.2 New sites must apply for a Standard Rules Permit where it is believed that landfill tax is applicable albeit at the lower £2.50 / tonne rate (and which is not on an escalator like the higher rate tax). These sites can normally also take soils (made ground) with slightly elevated contaminants. Therefore, unless construction arisings are significantly contaminated or there are no exempt sites nearby, only then would you need to use an official landfill i.e. one with a bespoke permit.

3.7.3 The other main consideration is that the majority of clean and lightly contaminated soils can be re-used on site and in our experience most contractors and developers at least have the objective of achieving this. It does require design of site levels to achieve a balance of excavated and reused material, including drainage arisings. There is a CL:AIRE CoP on re-using soils on sites. It was produced because the industry recognised that if it did not find a solution of its own, there would be nowhere to take arisings from sites. The CoP allows reuse of clean and contaminated materials on site. The CoP also allows the import of clean and contaminated materials (with or without treatment but with risk assessment) from one site to another as part of a Cluster arrangement.

3.7.4 At the present, costs for offsite disposal of clean material or perhaps elevated non mobile inorganic contaminants are very similar to historic earthwork disposal prices. Since the introduction of the Environmental Permitting Regulations 2010 (as amended), disposal of lightly contaminated soils has actually become easier and cheaper. Soil treatment centres are also becoming more common and whilst haulage and disposal / treatment costs are higher, these avoid the higher rate landfill tax and issues with waste acceptance criteria due to spurious chemical test results.

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4 Additional Operational and Maintenance Costs

4.1 Approach to the Costs 4.1.1 The costings detailed below define the additional costs associated with a scheme compliant with

Building Regulations to that compliant with the Draft Secretary of State’s Standards.

4.2 Additional Operational and Maintenance Costs 4.2.1 In considering additional operational costs, it has been assumed that all sewers and lateral drains

connecting to the public sewer system will in future transfer to the sewerage undertaker.

4.2.2 In modern estates, rear garden are now enclosed with high fences to reduce the risk of crime. Since in most households all adults are at work during the day, it is frequently the case that the Sewerage Undertaker cannot get permission to enter the rear garden of a neighbouring property to clear a blockage. In some cases where there are neighbour disputes, a neighbour has refused to give such permission.

4.2.3 Although Sewerage Undertakers have legal powers of entry onto private land to maintain their sewers, they can only exercise these powers by first giving notice and after obtaining a Magistrate’s Warrant. This takes time and incurs costs.

4.2.4 The additional costs that would accrue is the additional cost of repeat visits to obtain access to inspection chambers which have been installed in inaccessible locations and the consequent increased risk of flooding from the delay.

4.2.5 Nationally the average blockage rate in public sewers is 0.49 blockages /km /yr (ref Ofwat June Returns 2011). However, this includes blockages in interceptor traps which only occur in older sewers, the blockage rate in new sewers is known to be less. A blockage rate of 0.25 blockages /km /yr has therefore been assumed which is a rate of blockages without interceptor traps (UKWIR 2007

4.2.6 It typically costs £ 120 to clear a blockage (UKWIR 2007). If a blockage clearance crew cannot gain access and a repeat visit is required, the additional cost will typically be £ 80 per repeat visit. It has been assumed that 75% of cases where the access is in a rear garden will require a second visit.

4.2.7 In 2010/11 (ref Ofwat June Returns 2011) 2.6% of all blockages on public sewers caused internal flooding of the property and 24.7 % caused external flooding. Clearly any significant delay in clearing the blockage increases the likelihood of flooding. It has been assumed that this increase will be a 50 % increase in the likelihood of an internal and external flooding.

Internal Flooding Costs: 4.2.8 The damage due to internal flooding has been calculated from the Benefits of Flood and Coastal

Defence: Techniques and Data for 2003. Taking the average costs of post 1985 housing (terrace, semi-detached, detached, bungalow and flat) and a social class C1, the average internal flooding cost (building fabric AND building inventory) is £23,000.



External Flooding Costs: 4.2.9 The costs associated with external flooding are the clean-up costs for a domestic property which

includes gardens, gravel area and drives. The table below outlines the different external pollution clean-up costs for a domestic property. Using the values below, an average clean-up cost of £4,750 is used.

Land Use / Property Type

Clean Up Procedure Cost

Domestic Property – External

i. The removal of solids and excess water.

Item i) only - £100 to £300 Items i) & ii) - £400 to £1000 Items i), ii), iii) & iv)- £3,000 to £5,000 Item v) – in the range £500 to £1,000

ii. The disinfection of flooded areas (the milder the disinfection the better – strong disinfectants can cause more harm than good to the garden)

iii. The replacement of plants etc. In extreme cases the replacement of a lawn.

iv. The replacement of garden furniture etc

v. The replacement of gravel

4.3 Key Findings

Small Development 4.3.1 Length of sewer that is accessible only from a chamber in an enclosed garden = nil

4.3.2 Therefore no additional operational costs.

Medium Development 4.3.3 Length of sewer that is accessible only from a chamber in an enclosed garden = 15m

4.3.4 Number of blockages expected per year = 0.25 x 15 /1000 = 0.00375 blockages per year

4.3.5 Additional cost of blockage clearance = £ 80 x 0.00375 x 0.75 = £0.23 per year

4.3.6 Increased risk of external flooding = £4,750 x (0.257 x 0.5) x 0.00375 = £2.28 per year

4.3.7 Increased risk of internal flooding = £23,000 x (0.026 x 0.5) x 0.00375 = £1.12 per year

4.3.8 Total increased cost = £3.63 per year.

Large Development 4.3.9 Length of sewer that is accessible only from a chamber in an enclosed garden = 184m

4.3.10 Number of blockages expected per year = 0.25 x 184 /1000 = 0.046 blockages per year

4.3.11 Additional cost of blockage clearance = £ 80 x 0.046 x0.75 = £2.76 per year

4.3.12 Increased risk of external flooding = £4,750 x (0.257 x 0.5) x 0.046 = £28.08 per year

4.3.13 Increased risk of internal flooding = £23,000 x (0.026 x 0.5) x 0.046 = £13.75 per year

4.3.14 Total increased cost = £44.59 per year.

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4.4 Administration costs 4.4.1 There are a number of costs associated with the administration costs these costs comprise:

The sewerage undertakers charges – which should reflect the reasonable costs incurred

The developer’s (or their consultant’s) costs of liaising with the water company

4.4.2 The sewerage undertaker’s costs contain a fixed cost associated with the admin of setting up an agreement as well as a variable cost, depending on the size and complexity of the development, of checking the design and inspection of the works. Where the submission is not compliant the exchange between the WaSC and the developer can add significantly to the costs.

4.4.3 WaSC currently charge 2.5% of works cost though there are differences between companies over what is and what is not included. Some include CCTV survey other expect the developer to pay for this separately.

4.4.4 DCWW are currently working under their own new regime and currently charging 2.5% of the works cost subject to a minimum of £250 (in their scheme of charges), though I understand this will be reviewed when they have a better idea what it is actually costing under the new arrangements.

4.4.5 The difference between the old and new regimes on this basis could be calculated on the 2.5% of the cost of the works that were not previously adopted. However since it is supposed to be cost reflective it will depend on the sequence of the work. If the main sewers are constructed before starting on the plot drainage as at present, then the additional cost will depend on the time on site. WaSC’s already prioritise inspection frequencies based on perceived risk taking into account their experience of the gang carrying out the construction. In theory therefore a developer employing a reliable contractor ought to pay less for inspection.

4.4.6 It also should be noted that all the additional costs are not entirely a function of the change in Standards but a more a function of the S104 review, approval, inspection and handover process.



5 Summary and Discussion of Key Issues

5.1 Summary of Costs 5.1.1 The table below provides a summary of the key costs for each of the schemes tested the costs reflect

the unit cost as defined by the schemes tested and we have excluded the cost of the additional demarcation chambers associated with complying with Sewers for Adoption.

#

*These ranges are generated by the amount of pipework which could be adopted after estimation cost or adoption

Differences between National Build Regs and Draft National Standard Standards

5.1.2 A number of key themes have been identified through the development of the report.

The accessibility required by the Draft National Standard is the same as that intended to be provided under current building regulations. However, the industry has developed layouts which comply with the Building Regulations whilst not providing the required accessibility.

The accessibility set out in the Draft National Standard aligns with the intentions of the Building Regulations to comply with the Water Industry Act 1991 as amended by the Water Act 2003 and also reflects the recommendations of SFA. This includes additional demarcation chambers and extra pipe work to ensure the sewers are accessible.

The Draft National Standards scheme generates lower costs compared to the Building Regulations scheme to the small and medium sites, when you take into account the cost of the extra chambers recommended by SFA7, which the industry currently provides. When you compare the two schemes without this adjustment the Draft National Standards scheme generates a higher cost.

For the large site the Draft National Standard layouts would be the same as those set out in SFA7.

For the large site the very formal courtyard layout required additional demarcation chambers and additional lengths of sewers to provide the accessibility and therefore the cost for the Draft National Standard layout was higher than the Building Regulations layout. This is again a result of the recommendations of SFA7 rather than new recommendation of the Draft National Standard. The courtyard layout restricted access options and therefore had higher costs than expected.

We investigated an alternative layout which drains to the front of the pipeline which was much more efficient in terms of additional demarcation chambers and lengths of sewer. Whilst no actual comparison is needed with Building Regulations it is likely that the additional cost would be greatly reduced from a cost of £83 to a saving of £302/ property.

The Maintenance/Operational costs for the systems varied between all three schemes and this is as likely to be a function of the historical layouts as much as new regulations. The administration costs have been put as a range as there is likely to be an increase in the cost of adoption but this could be offset by the reduced work required for building regulations approvals.

Examples Small Medium Large

Change in CAPEX Cost to developers -£28 -£73 £0

Inspection fees No change No change No change

Admin Costs for developers and WaSCs* Based upon a fee up to 2.5% of the cost of additional adoption.

£0- 10.5 £0 -25.4

£0- 15.7

Per property -£ 17.50 -> -£28.5 - £57.15 -> -£73 £0 - £15.7

Appendices


Project number: 50600471 Dated: 28/03/2013 Revised: 19 April 2013

APPENDIX A Small Site Building Regulations - Layouts, Calculations and Costs

101

51-52

5354

SH

SH

107

102

103

105

106

108

109

119

12080

81

SH

SH

SH

SH

WSP Group Ltdc

Small site - Building Regulations

Item No Assumed item from SPONs Price Book SPONS Reference Unit Quantity Rate (£) Total (£)

ManholesMain sewer manholes in highway

Foul manhole in public highway - Assume this has to meet SfA 7 requirementsPrecast concrete construction withCircular shafts150mm plain concrete C15/20 surround225mm plain concrete C20/20 base slabPrecast reducing slabPrecast top slabMaximum ht of working chamber 2m above benching750mm diameter access shaftPlain concrete C15/20 benching, 150mm clay main channel longitudinally and two 100mm branch channels

Step irons at 300mm centre, doubled if depth to invert exceeds 3m

Heavy duty manhole cover and frameIn manholes over 6m deep, landings at maximum intervalsIncludes excavation, support, backfilling and disposal

1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 1 £1,351.15 £1,351.151200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 4 £1,434.15 £5,736.60

Extra over for concrete surround to meet SfA 7 requirement to GEN3 aggresive ground conditions

None - this is a typical foundation mix.

Extra over for 1200mm min dia access shaft to meet SfA 7 requirements

No difference as depths are too shallow to require access shaft

Extra over for 300mm concrete surround 1500 depth

1 x 1.17m3 Rate for mass concrete PC for concrete stool and thrust blocks Page 241. Only materials allowed for - extra cost of placing wider concrete surround is marginal.

m3 1.17 £62.15 £72.72



m3 6.24 £62.15 £387.82

Part H inspection chamber - Does not meet SfA 7 standard

Inspection chambers polypropylene (Hepworth plc)Up to 1.2m deep including polymer chamber and cover and frame with screw down lidExcavationBackfillingDisposal

Type 4 Access chamber in garden

Inspection chamber 300mm diameter, 600mm deep Landscaping and external works Page 365 No 1 £211.63 £211.63

Type 4 Inspection chamber in garden or shared access

Inspection chamber 450mm diameter, 1200mm deepLandscaping and external works Page 365, 475mm dia chamber

No 8 £375.60 £3,004.80

Type 3 Inspection chambers in shared access


No 3 £375.60 £1,126.80

Extra over for granular basePage 279 Type 1 use material cost only as cost of laying is marginal. m3 10.09 £24.35 £245.69

Extra over for 300mm Type 1 surround 600mm deep m3 0.34 £24.35 £8.28Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 7.81 £24.35 £190.17


Extra over for inspection chamber located in area subject to vehicle loading. Iron frame and cover

Those in shared access driveway and parking use rate for access cover and frame for concrete manholes (£350). Note a few ICs exceed 1200mm deep but this will not signficantly affect costs

No 3 £350.00 £1,050.00

Pipes

Main sewers in roadVitrified clay pipes to BSEN295 plain ends with push fit polypropylene couplings 150mm pipes in trenches ne 1.5m deep

Civil Engineering and Highway Works Page206 m 74 £46.52 £3,442.48

Extra over for backfill with Type 1Use material cost only as compaction, etc remains the same. m3 50 £24.35 £1,217.50

Sewers under shared access 100mm

Unplasticized PVC pipes ring seal sockets excavation and supports backfilling 6m ppe lengths 110mm pipes in trenches ne 1.5m deep

Civil Engineering and Highway Works Page218 m 37 £26.36 £975.32

Extra over for backfill with Type 1 m3 25 £24.35 £608.75

Private connections predominantly in gardens or under slabs 100mm



Pipe bedding Imported granular material - 100mm deep bed for 100mm dia pipe Civil Engineering and Highway Works Page238 m 209 £3.20 £668.80

Imported granular material - 150mm deep bed for 150mm dia pipe Civil Engineering and Highway Works Page238 m 74 £7.36 £544.64

Pipe surroundImported granular material - 100mm deep surround for 100mm dia pipe


Imported granular material - 150mm deep surround for 150mm dia pipe


Total Cost for comparison purposes - Small site Building Regs

£28,629.90

Assumptions

Note these comments relate to foul systems in accordance with Part H and as such the pipes are no greater than 150mm and thus all manholes to be 1200 diameter PCC Ring chambers, with 300mm of concrete surround. This is based on the common practise of over excavating the void for the manhole, and allows proper compaction of the concrete in compliance with the specification. The cost of correct materials and methods for larger voids is likely to be similar to the notional 300 of concrete.

ICs are to be 450 plastic chambers with 300mm surround of type 1 material. Again, this thickness of surround is specified to allow proper compaction of the granular material.

All backfill to pipe runs beneath carriageways to be compacted Type 1 material.

Backfill to pipes within landscaped areas may be as-dug material

All pipe bedding assumed to be class S (full granular bed and surround)

Pipework may be clay or plastic, as long as it is compliant with the standards set out in SFA 7th - assume plastic off highway and clay in highway

Cover sizes to be in accordance with the relevant guidance document – SFA 7th or Building Regs Doc H. Note the access restriction to 450 plastic chambers in SFA 7th.

Surplus material is able to be disposed within the site

Connections to existing manhole not included - same for both options

APPENDIX B Small Site Draft Secretary of State’s Standards - Layout, Calculations and Costs

101

51-52

5354

SH

SH

107

102

103

105

106

108

109

119

12080

81

SH

SH

SH

SH

WSP Group Ltdc

Small site - SFA 7






1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 1 £1,351.15 £1,351.151200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 4 £1,434.15 £5,736.60







m3 1.17 £62.15 £72.72



m3 6.24 £62.15 £387.82

Part H inspection chamber - Does not meet SfA 7 standard

Inspection chambers polypropylene (Hepworth plc)Up to 1.2m deep including polymer chamber and cover and frame with screw down lidExcavationBackfillingDisposal



Type 4 Inspection chamber in garden - Private


No 9 £375.60 £3,380.40

Type 4 Inspection chamber in garden - Sewer


No 4 £375.60 £1,502.40

Type 3 Inspection chambers in garden


No 2 £375.60 £751.20

Extra over for granular basePage 279 Type 1 use material cost only as cost of laying is marginal. m3 13.5 £24.35 £328.73

Extra over for 300mm Type 1 surround 600mm deep m3 0.34 £24.35 £8.28Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 10.65 £24.35 £259.33



Those in shared access driveway and parking use rate for access cover and frame for concrete manholes (£350). Note a few ICs exceed 1200mm deep but this will not signficantly affect costs

No 0 £350.00 £0.00

Pipes

Main sewers in roadVitrified clay pipes to BSEN295 plain ends with push fit polypropylene couplings 150mm pipes in trenches ne 1.5m deep







Laterals under shared access 100mm




Private connections predominantly in gardens or under slabs 100mm



Pipe bedding Imported granular material - 100mm deep bed for 100mm dia pipe Civil Engineering and Highway Works Page238 m 206 £3.20 £659.20






Total Cost for comparison purposes - Small site SFA 7

£29,236.08

Assumptions

APPENDIX C Medium Site Building Regulations - Layout, Calculations and Costs

2221

1

2

3

4

5

6

7

11

12

13

14

15

16

17

26

27

20

23

24

2518-19

28

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

8

9

10SH

SH

SH

14

31

32

30

29

2221

1

2

3

4

5

6

7

11

12

13

14

15

16

17

26

27

20

23

24

2518-19

31

32

30

29

28

8

9

10

WSP Group Ltdc

Medium site - Building Regs






1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 2 £1,351.15 £2,702.301200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 3 £1,434.15 £4,302.451200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 3 £1,816.15 £5,448.451200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 0 £2,061.65 £0.00







m3 2.34 £62.15 £145.43


Rate for mass concrete PC for concrete stool and thrust blocks Page 241. Only materials allowed for - extra cost of placing wider concrete surround is marginal.

m3 4.68 £62.15 £290.86



m3 5.82 £62.15 £361.71



m3 0 £62.15 £0.00

Sewer manholes in shared access

1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 3 £1,351.15 £4,053.45

1200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 4 £1,434.15 £5,736.601200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,816.15 £0.001200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 0 £2,061.65 £0.00







m3 3.51 £62.15 £218.15



m3 6.24 £62.15 £387.82



m3 0 £62.15 £0.00



m3 0 £62.15 £0.00

Part H inspection chamber - Does not meet SfA 7 standardInspection chambers polypropylene (Hepworth plc)Up to 1.2m deep including polymer chamber and cover and frame with screw down lidExcavationBackfillingDisposal



Type 4 Inspection chamber in garden/footway/footpath - Private

Inspection chamber 450mm diameter, 1200mm deep Landscaping and external works Page 365, 475mm dia chamber

No 30 £375.60 £11,268.00

Type 4 Inspection chamber in private parking - Sewer

Inspection chamber 450mm diameter, 1200mm deepLandscaping and external works Page 365, 475mm dia chamber No 9 £375.60 £3,380.40

Type 4 Inspection chamber in garden/footway/footpath - Sewer


No 0 £375.60 £0.00



No 0 £375.60 £0.00


Inspection chamber 450mm diameter, 1200mm deepLandscaping and external works Page 365, 475mm dia chamber No 0 £375.60 £0.00


Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 0 £431.94 £0.00

Extra over for granular base Page 279 Type 1 use material cost only as cost of laying is marginal. m3 32 £24.35 £779.20

Extra over for 300mm Type 1 surround 600mm deep m3 0 £24.35 £0.00Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 26 £24.35 £633.10Extra over for 300mm Type 1 surround 1500mm deep Assume average depth of ICs is 1.5m. m4 0 £25.35 £0.00

Type 3/4 Inspection chambers in shared access or private parking


Those in shared access driveway and parking use rate for access cover and frame for concrete manholes (£350)

No 9 £350.00 £3,150.00

Pipes

Main sewers in road/shared access

Vitrified clay pipes to BSEN295 plain ends with push fit polypropylene couplings 100mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page205 m 34 £32.30 £1,098.20

ne 2.0m deep Civil Engineering and Highway Works Page206 m 0 £37.78 £0.00

Vitrified clay pipes to BSEN295 plain ends with push fit polypropylene couplings 150mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page206 m 91 £46.52 £4,233.32

ne 2.0m deep Civil Engineering and Highway Works Page206 m 134 £50.53 £6,771.02ne 2.5m deep Civil Engineering and Highway Works Page206 m 0 £55.83 £0.00

Extra over for backfill with Type 1 Use material cost only as compaction, etc remains the same. m3 174 £24.35 £4,236.90

Private under shared access, highway or private parking 100mm



ne 2.0m Civil Engineering and Highway Works Page218 m 11 £30.35 £333.85ne 2.5m Civil Engineering and Highway Works Page218 m 0 £34.32 £0.00

Extra over for backfill with Type 1 Use material cost only as compaction, etc remains the same. m3 67 £24.35 £1,631.45

Sewer under path 100mm

Unplasticized PVC pipes ring seal sockets excavation and supports backfilling 6m ppe lengths 110mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page218 m 0 £26.36 £0.00




Extra over for backfill with Type 1 Use material cost only as compaction, etc remains the same. m3 17 £24.35 £413.95

Laterals under shared access or highway 100mm

Unplasticized PVC pipes ring seal sockets excavation and supports backfilling 6m ppe lengths 110mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page206 m 0 £26.36 £0.00


Extra over for backfill with Type 1 Use material cost only as compaction, etc remains the same. m3 0 £24.35 £0.00

Private connections in gardens 100mm

Unplasticized PVC pipes ring seal sockets excavation and supports backfilling 6m ppe lengths 110mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page206 m 148 £26.36 £3,901.28



Unplasticized PVC pipes ring seal sockets excavation and supports backfilling 6m ppe lengths 160mm pipes in trenches ne 1.5m deep Civil Engineering and Highway Works Page218 m 31 £51.48 £1,595.88

Pipe bedding Imported granular material - 100mm deep bed for 100mm dia pipe Civil Engineering and Highway Works Page238 m 335 £3.20 £1,072.00

Imported granular material - 150mm deep bed for 150mm dia pipe Civil Engineering and Highway Works Page238 m 282 £7.36 £2,075.52

Pipe surround Imported granular material - 100mm deep surround for 100mm dia pipe




Total Cost for comparison purposes - Medium site Building Regs

£82,973.81£72,271.08

Plus need to take into account variations in underslab drainage not included in above

Assumptions










APPENDIX D Medium Site Draft Secretary of State’s Standards - Layout, Calculations and Costs

2221

1

2

3

4

5

6

7

11

12

13

14

15

16

17

26

27

20

23

24

2518-19

28

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

SH

8

9

10SH

SH

SH

14

31

32

30

29

2221

1

2

3

4

5

6

7

11

12

13

14

15

16

17

26

27

20

23

24

2518-19

31

32

30

29

28

8

9

10

WSP Group Ltdc

Medium site - SoS






1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 1 £1,351.15 £1,351.151200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,434.15 £0.001200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 4 £1,816.15 £7,264.601200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 2 £2,061.65 £4,123.30







m3 1.17 £62.15 £72.72



m3 0 £62.15 £0.00



m3 7.76 £62.15 £482.28



m3 4.66 £62.15 £289.62






No 23 £375.60 £8,638.80

Type 4 Inspection chamber in private parking - Sewer


No 7 £375.60 £2,629.20

Type 4 Inspection chamber in garden/footway/footpath - Sewer


No 3 £375.60 £1,126.80



No 3 £375.60 £1,126.80



No 13 £375.60 £4,882.80



Extra over for granular basePage 279 Type 1 use material cost only as cost of laying is marginal. m3 44.2 £24.35 £1,076.27

Extra over for 300mm Type 1 surround 600mm deep m3 0 £24.35 £0.00Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 34.79 £24.35 £847.14Extra over for 300mm Type 1 surround 1500mm deep Assume average depth of ICs is 1.5m. m4 2.12 £25.35 £53.74




No 22 £350.00 £7,700.00

Pipes

Main sewers in roadVitrified clay pipes to BSEN295 plain neds with push fit polypropylene couplings 100mm pipes in trenches ne 1.5m deep


ne 2.0m deep Civil Engineering and Highway Works Page206 m 78 £37.78 £2,946.84

Vitrified clay pipes to BSEN295 plain neds with push fit polypropylene couplings 150mm pipes in trenches ne 1.5m deep


ne 2.0m deep Civil Engineering and Highway Works Page206 m 7 £50.53 £353.71ne 2.5m deep Civil Engineering and Highway Works Page206 m 82 £55.83 £4,578.06







Sewer under path 100mm











Laterals or private connections in gardens










Extra length of pipe is m 10 £26.36 £263.60

Total Cost for comparison purposes - Medium site SFA 7

£83,865.31

Assumptions


APPENDIX E Large Site Building Regulations – Layout, Calculations and Costs

WSP Group Ltdc

Large site - Building Regs






1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 14 £1,351.15 £18,916.101200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 4 £1,434.15 £5,736.601200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 7 £1,816.15 £12,713.051200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 5 £2,061.65 £10,308.25







m3 16.4 £62.15 £1,019.26



m3 6.2 £62.15 £385.33



m3 13.6 £62.15 £845.24



m3 11.7 £62.15 £727.16



1200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 1 £1,434.15 £1,434.151200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,816.15 £0.001200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 0 £2,061.65 £0.00







m3 11.7 £62.15 £727.16



m3 1.6 £62.15 £99.44



m3 0 £62.15 £0.00



m3 0 £62.15 £0.00

Part H inspection chamber - Does not meet SfA 7 standardInspection chambers polypropylene (Hepworth plc)Up to 1.2m deep including polymer chamber and cover and frame with screw down lidExcavationBackfilling

Disposal





No 186 £375.60 £69,861.60

Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 2 £431.94 £863.88Type 4 Inspection chamber in private parking or shared access - Sewer


No 8 £375.60 £3,004.80

Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 8 £431.94 £3,455.52Type 4 Inspection chamber in garden/footway/footpath - Sewer


No 0 £375.60 £0.00



No 0 £375.60 £0.00



No 0 £375.60 £0.00



Extra over for granular basePage 279 Type 1 use material cost only as cost of laying is marginal. m3 175 £24.35 £4,261.25

Extra over for 300mm Type 1 surround 600mm deep m3 0 £24.35 £0.00Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 206 £24.35 £5,016.10Extra over for 300mm Type 1 surround 1500mm deep Assume average depth of ICs is 1.5m. m4 14 £25.35 £354.90




No 16 £350.00 £5,600.00

Pipes


Vitrified clay pipes to BSEN295 plain ends with push fit polypropylene couplings 100mm pipes in trenches ne 1.5m deep





ne 2.0m deep Civil Engineering and Highway Works Page206 m 242 £50.53 £12,228.26ne 2.5m deep Civil Engineering and Highway Works Page206 m 138 £55.83 £7,704.54ne 3.0m deep Civil Engineering and Highway Works Page206 m 203 £62.49 £12,685.47


Sewer under shared access or private parking 100mm







Sewer under garden/path 100mm




Sewer under garden/path 150mm






Extra over for backfill with Type 1Use material cost only as compaction, etc remains the same. m3 0 £24.35 £0.00





Extra over for backfill with Type 1Use material cost only as compaction, etc remains the same. m3 0 £24.35 £0.00








ne 2.0m Civil Engineering and Highway Works Page218 m 27 £55.51 £1,498.77







Total Cost for comparison purposes - Large site Building Regs

£326,129.29

There are no variations in underslab drainage Underslab drainage is not included in above

Assumptions

APPENDIX F Large Site Draft Secretary of State’s Standards – Layout, Calculations and Costs

WSP Group Ltdc

Large site - SFA 7







1200mm diameter x 3500 depth to invertCivil Engineering and Highway Works Page231 use rate for 1800mm dia by 3500 depth

No 1 £4,446.85 £4,446.85







m3 19 £62.15 £1,180.85



m3 11 £62.15 £683.65



m3 2 £62.15 £124.30



m3 9 £62.15 £559.35



m3 2.7 £62.15 £167.81



1200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,434.15 £0.001200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,816.15 £0.001200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 0 £2,061.65 £0.00







m3 4 £62.15 £248.60



m3 0 £62.15 £0.00



m3 0 £62.15 £0.00



m3 0 £62.15 £0.00






No 38 £375.60 £14,272.80



No 0 £375.60 £0.00

Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 0 £431.94 £0.00Type 4 Inspection chamber in garden/footway/footpath - Sewer


No 111 £375.60 £41,691.60



No 0 £375.60 £0.00



No 14 £375.60 £5,258.40


Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 7 £431.94 £3,023.58


Extra over for 300mm Type 1 surround 600mm deep m3 0 £24.35 £0.00Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 116 £24.35 £2,824.60Extra over for 300mm Type 1 surround 1500mm deep Assume average depth of ICs is 1.5m. m4 8 £25.35 £202.80




No 21 £350.00 £7,350.00

Pipes







ne 2.0m deep Civil Engineering and Highway Works Page206 m 197 £50.53 £9,954.41ne 2.5m deep Civil Engineering and Highway Works Page206 m 66 £55.83 £3,684.78ne 3.0m deep Civil Engineering and Highway Works Page206 m 84 £62.49 £5,249.16ne 3.5m deep Civil Engineering and Highway Works Page207 m 25 £75.76 £1,894.00










ne 2.0m Civil Engineering and Highway Works Page218 m 16 £55.51 £888.16


Sewer/private under garden/path 100mm



ne 2.0m Civil Engineering and Highway Works Page218 m 9 £30.35 £273.15ne 2.5m Civil Engineering and Highway Works Page218 m £34.32 £0.00











Total Cost for comparison purposes - Large site SFA7 £260,707.77


Extra costs if have to dig through existing road and reinstate

Excavate tarmacadam surface exposed at commencing surface ne 0.25m maximum depth

Civil Engineering and Highway Works Page 162 assume width is 450mm and 522m length m3 59 £24.81 £1,463.79

Reinstate asphalt surface £0.00

100mm DBM Base

Civil Engineering and Highway Works Page 280 assume width is 450mm and 522m length (note this is for large highways schemes so there will be an uplift for small works and hand laying - say 30%

m3 24 £18.10 £434.40 Base rate without uplift £18.91

100mm DBM BinderCivil Engineering and Highway Works Page 280 assume width is 450mm and 522m length m3 24 £16.78 £402.72

Base rate without uplift £12.91

30mm DBM SurfaceCivil Engineering and Highway Works Page 280 assume width is 450mm and 522m length m3 7 £7.86 £55.02

Base rate without uplift £6.05

Total extra over £2,355.93

Assumptions










Large site - SoS







1200mm diameter x 3500 depth to invertCivil Engineering and Highway Works Page231 use rate for 1800mm dia by 3500 depth

No 1 £4,446.85 £4,446.85







m3 22.2 £62.15 £1,379.73



m3 11 £62.15 £683.65



m3 7.8 £62.15 £484.77



m3 4.7 £62.15 £292.11



m3 2.7 £62.15 £167.81


1200mm diameter x 1500 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,351.15 £0.00

1200mm diameter x 2000 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,434.15 £0.001200mm diameter x 2500 depth to invert Civil Engineering and Highway Works Page229 No 0 £1,816.15 £0.001200mm diameter x 3000 depth to invert Civil Engineering and Highway Works Page229 No 0 £2,061.65 £0.00







m3 £62.15 £0.00



m3 £62.15 £0.00



m3 £62.15 £0.00



m3 £62.15 £0.00

Part H inspection chamber - Does not meet SfA 7 standardInspection chambers polypropylene (Hepworth plc)

Up to 1.2m deep including polymer chamber and cover and frame with screw down lidExcavationBackfillingDisposal





No 124 £375.60 £46,574.40



No 0 £375.60 £0.00

Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 0 £431.94 £0.00Type 4 Inspection chamber in garden/footway/footpath - Sewer


No 144 £375.60 £54,086.40



No 0 £375.60 £0.00



No 40 £375.60 £15,024.00


Inspection chamber 450mm diameter, 1500mm deep See separate cost breakdown No 4 £431.94 £1,727.76


Extra over for 300mm Type 1 surround 600mm deep m3 0 £24.35 £0.00Extra over for 300mm Type 1 surround 1200mm deep Assume average depth of ICs is 1m. m3 218 £24.35 £5,308.30Extra over for 300mm Type 1 surround 1500mm deep Assume average depth of ICs is 1.5m. m4 4.2 £25.35 £106.47




No 44 £350.00 £15,400.00

Pipes




ne 2.0m deep Civil Engineering and Highway Works Page206 m 90 £37.78 £3,400.20



ne 2.0m deep Civil Engineering and Highway Works Page206 m 128 £50.53 £6,467.84ne 2.5m deep Civil Engineering and Highway Works Page206 m 85 £55.83 £4,745.55ne 3.0m deep Civil Engineering and Highway Works Page206 m 133 £62.49 £8,311.17










ne 2.0m Civil Engineering and Highway Works Page218 m 22 £55.51 £1,221.22





ne 2.0m Civil Engineering and Highway Works Page218 m £30.35 £0.00ne 2.5m Civil Engineering and Highway Works Page218 m £34.32 £0.00











Total Cost for comparison purposes - Large site SFA7 £378,398.82


Assumptions






WSP UK Limited Mountbatten House Basing View Basingstoke RG21 4HJ UK Tel: +44 (0)1256 318800 Fax: +44 (0)1256 318700 www.wspgroup.co.uk