Case study: Designing out Waste Southgate College ... College... · Front cover photography: Artists impression (Dyer Architects) WRAP and Davis Langdon believe the content of this

Case study: Designing out Waste

Southgate College redevelopment

A design review of the project to redevelop Southgate College in Enfield identified easy to implement ideas to reduce construction waste with the potential to reduce total project costs by £116,254, reduce the amount of waste produced on site by 617 tonnes and avoid 94 lorry movements from the site.

Project code: WAS400-002 Research date: July 2008 – March 2009 Date: March 2010

WRAP’s vision is a world without waste, where resources are used sustainably. We work with businesses and individuals to help them reap the benefits of reducing waste, develop sustainable products and use resources in an efficient way. Find out more at www.wrap.org.uk

Written by: Davis Langdon

Front cover photography: Artists impression (Dyer Architects) WRAP and Davis Langdon believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.). The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain whether a particular product will satisfy their specific requirements. The listing or featuring of a particular product or company does not constitute an endorsement by WRAP and WRAP cannot guarantee the performance of individual products or materials. This material is copyrighted. It may be reproduced free of charge subject to the material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must not be used to endorse or used to suggest WRAP’s endorsement of a commercial product or service. For more detail, please refer to WRAP’s Terms & Conditions on its web site: www.wrap.org.uk

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Executive summary Designing out Waste during the design stage of a construction project presents a significant opportunity to reduce waste from occurring on site, reducing the construction industry’s waste burdens and improving the efficiency of material usage. These can provide clear cost savings and reductions in embodied carbon. Through working with design teams on live projects, WRAP (Waste & Resources Action Programme) has created a series of exemplar case studies which demonstrate the benefits of taking action at the design stage to reduce waste and embodied carbon by making changes that either saved money or were cost neutral based on the five key principles of Designing out Waste:

Design for Reuse and Recovery;

Design for Off Site Construction;

Design for Material Optimisation;

Design for Waste Efficient Procurement; and

Design for Deconstruction and Flexibility.

This report describes the work conducted by WRAP with Dyer Architects to demonstrate these principles in practice by identifying cost-effective and feasible waste reducing opportunities in the design of the Southgate College redevelopment project. The Designing out Waste process comprises three stages:

Identify – engagement with the design team in a design review workshop to identify and prioritise

opportunities to reduce waste based on the five key principles of Designing out Waste;

Investigate – qualitative and quantitative analysis of prioritised alternative designs compared with the base

design, including calculation of cost, waste and carbon savings; and

Implement – selection of solutions to implement into the design and build based on the outcome of this

analysis.

The ideas generated at the workshop were evaluated by the design team in terms of their waste reduction potential and their feasibility for implementation on the project. Three of these ideas were selected as being the most appropriate for quantitative analysis:

prefabricated classroom pods instead of conventional construction of classrooms on site;

precast concrete columns instead of conventional cast in situ concrete columns; and

geocellular sustainable drainage system (SUDS) for water collection instead of a traditional tank storage

solution.

A comparative assessment of these three opportunities to reduce waste (i.e. base design versus alternative design) was undertaken to determine the difference in the overall construction cost, quantity of waste, number of lorry movements avoided, cost of waste disposal and the value of material wasted. The table below summarises the results of this assessment for the three design solutions. Implementing the three alternative designs would:

reduce total project costs by £116,254;

reduce waste arisings on site by 617 tonnes;

reduce embodied carbon by 85 tonnes;

avoid 94 lorry movements;

reduce waste disposal costs by £21,424; and

reduce the value of materials wasted by £24,487.

The effect of fewer lorry movements from the site would not only reduce the overall energy consumption of the construction process but also local nuisance impacts such as noise and dust, and wear and tear to the local infrastructure.

Southgate College redevelopment 1


Results of quantitative analysis of design solutions for the Southgate College redevelopment project

Design solution

Total project cost

A saving

Reduction in waste (tonnes)

Reduction in

embodied carbon of

waste (tonnes) B

Number of lorry

movements avoided C

Reduction in cost of

waste disposal

Reduction in value of

wasted materials

Prefabricated classroom construction

£61,382 246 46 52 £9122 £3956

Precast concrete columns

£41,262 36 24 4 £560 £20,531

SUDS (geocellular system)

£13,610 335 15 38 £11,742 £0

Total £116,254 617 85 94 £21,424 £24,487

A: Cost of construction + waste disposal cost B: Does not include carbon impact of transporting waste or recycling/recovery/disposal method. C: Based on collections of 8yd3 (6.1m3) skips, and 15 m3 lorry movements for bulk haulage of excavation waste.


Contents 1.0 Introduction ............................................................................................................................. 4

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101010111112121313131415152124

1.1 The construction scheme ....................................................................................................... 1.2 The project team...................................................................................................................

2.0 Designing out Waste process................................................................................................... 2.1 Design review workshop ........................................................................................................

2.1.1 Awareness session .................................................................................................... 2.1.2 Creativity session ...................................................................................................... 2.1.3 Reasoning session.....................................................................................................

2.2 Quantitative analysis.............................................................................................................. 2.2.1 Calculate .................................................................................................................. 2.2.2 Compare ................................................................................................................

3.0 Cost, waste and carbon reductions from selected solutions.................................................. 3.1 Prefabricated classroom construction .................................................................................... 3.2 Precast columns .................................................................................................................. 3.3 SUDS (geocellular solution) ..................................................................................................

4.0 Discussion .............................................................................................................................. 4.1 Potential savings ................................................................................................................. 4.2 Comments on the design solutions .......................................................................................

4.2.1 Prefabricated classroom pods .................................................................................. 4.2.2 Precast columns...................................................................................................... 4.2.3 SUDS (geocellular solution) .....................................................................................

Appendix A Quantitative analysis results........................................................................................... Prefabricated classroom construction................................................................................................. Precast columns versus cast in situ ................................................................................................... SUDS versus tank storage of storm water ..........................................................................................


1.0 Introduction The construction industry is the biggest user of materials in the UK economy, consuming more than 400 million tonnes of materials each year. It also generates over 120 million tonnes of construction, demolition and excavation waste each year – over a third of all waste – only half of which is currently recycled or reclaimed back into construction. The WRAP Construction Programme is helping the construction industry cut costs and increase efficiency through the better use of materials and reduction in waste. It aims to set new standards for good and best practice in resource and waste management in the construction industry, and provides free access to tools and knowledge to allow clients, designers and contractors to increase the materials resource efficiency of their projects and to increase industry awareness of the commercial benefits of doing so. The best opportunities to reduce materials use and waste in construction occur by working at the earliest stages possible in the construction process. Empowering design teams to identify and act upon these opportunities to design out waste is therefore key to achieving the Government’s and industry’s commitment to Halving Waste to Landfill by 2012. Decisions made throughout the evolution of a design can have a major impact on the levels of materials used during a project and waste that arises during the physical construction and future demolition. Often these decisions are made based on considerations such as site constraints, client requirements for improved performance or finish, or compliance with Building Regulations but, currently, these considerations rarely include improving materials resource efficiency or reducing waste. ‘Designing out Waste’ during the design stage presents a major opportunity to prevent the creation of waste on site thus improving resource efficiency, reducing waste to landfill and saving carbon – and reducing project costs. The five key principles of Designing out Waste are:

Design for Reuse and Recovery;

Design for Off Site Construction;

Design for Material Optimisation;

Design for Waste Efficient Procurement; and

Design for Deconstruction and Flexibility.

WRAP has worked closely with the construction industry to develop a simple three-step structured process for ‘Designing out Waste’ to help design teams apply these principles to reduce the amount of construction waste produced through early changes to design, specification and procurement. A guide, Designing out Waste: A design team guide for buildings,1 presenting this Designing out Waste process was published by WRAP in June 2009 and is recognised by RIBA within its CPD Core Curriculum. This report describes work conducted as part of a WRAP project to work with the design teams of major live construction projects. The WRAP project had four main objectives:

to identify opportunities to reduce the amount of construction, demolition and excavation waste produced at

the outline design stage;

to positively influence projects by gaining client, contractor and design team buy in to identify and adopt

appropriate waste reduction design solutions;

to gather evidence of the waste, cost and embodied carbon savings as a result of the adopted solutions; and

to follow and test WRAP’s design guidance and Designing out Waste process.

A number of construction projects were selected to be involved in this WRAP project and to produce exemplar case studies. This report summarises the findings of work by Davis Langdon (on behalf of WRAP) conducted with Dyer Architects to identify and investigate opportunities for Designing out Waste on the project to redevelop Southgate College in Enfield, north London.

1 Available from the WRAP website (www.wrap.org.uk/designingoutwaste)

1.1 The construction scheme The project is part of a new college campus in Enfield, north London in an area of low-rise mixed residential and commercial usage that surrounds the busy underground station and bus interchange of Southgate. The construction value of the project is £44.4 million. At the time of writing, the project had just completed RIBA Stage C with RIBA Stage D imminent. The construction process is to be phased to minimise impact upon the school curriculum, with planning approval expected in April 2009 and an anticipated start on site in late 2010. The project is to be developed as a two-stage Design & Build contract. Phase 1 involves the construction of entrance buildings and landscaping for a new public square along the high street, and Phase two the demolition of existing facilities and construction of remaining facilities with atrium and courtyard spaces. The redeveloped campus will incorporate a new theatre, restaurant, hair/beauty salons and fitness suite along teaching accommodation and an energy centre showcasing sustainable technologies. The project is targeting a BREEAM rating of ‘Excellent’ and aspires to be one of the most sustainable developments in Enfield. 1.2 The project team Davis Langdon was contracted by WRAP to:

facilitate the design review workshop (see section 2);

carry out the subsequent cost, waste and environmental assessments; and

develop the exemplar case study.

The project team is made up of:

Dyer Architects (architects);

GVA Grimley (project manager)

Faithful & Gould (quantity surveyor);

Faber Maunsell (structural and drainage engineer);

Hoare Lee (M&E engineer and sustainability consultants); and

Davis Langdon Schumann Smith (specification consultants).

2.0 Designing out Waste process The Designing out Waste process devised by WRAP involves three stages: 1 Identify alternative design solutions which reduce materials use and/or creation of waste, and prioritise

those that will have the biggest impact and be easiest to implement. This stage requires some form of design review, and WRAP’s Designing out Waste guide presents the format for a facilitated design review workshop which ensures a robust approach involving all the design team.

2 Investigate the prioritised solutions further and quantify the benefits in terms of reductions in waste, cost and carbon. This enables evidence-based decision-making on which design solutions to implement.

3 Implement the agreed solutions in the project through the plans, specifications and contracts. Record the solutions in the Site Waste Management Plan to ensure they are fully communicated to the contractor and the quantified benefits are communicated to the client.

Designing out Waste: a design team guide for buildings recommends undertaking the design review workshop during RIBA Stage C. 2.1 Design review workshop The design review workshop was held on 16 December 2008 at Dyer’s offices in London. It was attended by:

Ray Fong, Project Architect;

Christopher Brown, GVA Grimley;

David Cuckow, Faber Maunsell;

Alison Leach, Faithful & Gould;

Daniel Kenning, Hoare Lea;

Alex Amato, Davis Langdon; and

Edwina McKechnie, Davis Langdon.


The workshop had three separate but consecutive sessions:

Awareness session – review of Designing out Waste principles, and summary of the construction project;

Creativity session – ideas generation; and

Reasoning session – ideas classification and prioritisation.

2.1.1 Awareness session The first session included a brief overview of WRAP’s construction programme, materials resource efficiency and the aims of the design review workshop. The design team then gave a short presentation on the Tate Modern 2 scheme, highlighting some of the specifications from the design brief and project restrictions. 2.1.2 Creativity session A brainstorming session was then undertaken where all members of the team were encouraged to suggest ideas of how waste could be prevented or reduced. The aim was to create an atmosphere where ideas were stimulated through people thinking ‘outside of the box’. Attendees were encouraged to ‘brainstorm’ a series of design opportunities that would effectively reduce construction waste in the project. The role of the facilitator was to encourage the design team to have a free flow of ideas, and to identify as many opportunities as possible. All ideas, regardless of feasibility, were recorded. 2.1.3 Reasoning session Following the brainstorming session, the ideas were then evaluated by the group for their waste reduction potential and their feasibility for implementation on the project in terms of cost, programme and quality. Although a rough initial assessment, this helped to quickly identify the top opportunities with the greatest impact on waste and the most likely to be pursued on the project. All ideas were prioritised by the team by classifying as either A, B, C or D as per the simple ‘opportunity’ matrix shown in Figure 1:

Section A – High impact on waste reduction, easy to implement.

Section B – High impact on waste reduction, difficult to implement.

Section C – Low impact on waste reduction, easy to implement.

Section D – Low impact on waste reduction, difficult to implement.

Once ideas were allocated to A, B, C or D, discussions focused on the top areas of opportunity to take forward. These were marked by a star on the note card. Table 1 lists all the ideas generated and their associated classification and categorisation in terms of impact on waste reduction/feasibility.

Figure 1 Opportunity matrix used to evaluate waste reduction ideas


Table 1 Ideas to reduce waste in design A – High impact on waste reduction, easy to implement

Reuse of demolition materials for piling mat. Reuse of demolition materials for landscape grading. Reuse and refurbish existing building. Reuse components of existing buildings off site, e.g. through reclamation. Reuse existing building structure and refurbish. Demolition waste reused on site.

Design for Reuse and Recovery

Phase 1 demolition – reuse materials externally. Off site prefabrication of frame, specifically columns. Off site prefabrication of cladding. Precast slabs. Use steel frame prefabricated units. Precast concrete structure – columns.

Design for Off Site Construction

Use of BubbleDeck® or similar alternative. Raised floor to reduce cutting. Standard room sizes – speak to manufacturers regarding ‘parts to fit’. Standardise heights, etc. to minimise offcuts.

Design for Materials Optimisation

Standardise/reduce number of specified materials and disallow ‘hard to recycle’ e.g. PVC. Rationalise vehicles bringing materials to site and taking materials away. Focus on inefficiencies of casting in situ (operatives) and target same efficiencies as with precast, i.e. efficient procurement of in situ concrete.

Design for Waste Efficient Procurement

Logistics – minimise wastage due to on site damage, etc. by using a local ‘off site materials depot’ for controlling the flow of materials to/from site.

Other Divert construction waste to college for its use during vocational training courses (BREEAM).

‘B’ – High impact on waste reduction, difficult to implement Reuse light fittings from existing buildings. Reuse façade to main building. Reuse demolition material as aggregate in concrete. Clean demolition – segregate materials at point of arising.


New façade on old building. Use prefabricated brick panels. Prefabricate fixtures, furnishings and equipment (FF&E).


Use of BubbleDeck® or similar alternative. Reduce size of car park. Adopt sustainable drainage system (SUDS) to save on tank and excavation (attenuation and rainwater harvesting together). Reuse timber (revenue).


Investigate companies that will buy packaging waste such as timber. Design for Deconstruction and Flexibility

Design for disassembly – screws versus glue.

‘C’ – Low impact on waste reduction, easy to implement Use lightweight building aggregate produced from pulverised fuel ash (PFA) in flat slab construction.


Cement replacements – pulverised fuel ash (PFA), ground granulated blast furnace (GGBS). Use pattern imprinted concrete in car park. Standardise on lamp design.


Maintainable finishes – not ‘no maintenance’ finishes. Design for Waste Efficient Procurement

Design/specify to reduce ongoing (operational) waste – materials that need replacing – life cycle approach.

Other Linking waste to College’s vocational construction course during construction period.

‘D’ – Low impact on waste reduction, difficult to implement



Reuse of ironmongery.


Prefabricate car park.

Design for Deconstruction and Flexibility

Design for disassembly – screws versus glue.

Other Facilities management and operational waste. Table 2 lists those ideas selected at the design review workshop for possible further investigation.

Table 2 Ideas selected at the workshop for further investigation Category Idea Ranking

Reuse demolition waste on site. A Reuse of existing building structure with refurbishment. A


Reuse Phase 1 demolition in external construction A

Precast concrete structure – columns. A Precast slabs. A


Prefabrication of FF+E. B Raised floor to reduce cutting. A Standard room sizes – speak to manufacturers about making ‘parts to fit’.

A

Standardise heights to minimise off cuts. A Standardise/reduce number of specified materials and disallow ‘hard to recycle’ materials, e.g. PVC.

A

Reduce the size of the car park. B


SUDS – save on tank excavation and combine runoff attenuation and rainwater harvesting storage.

B

Design for Waste Efficient Procurement

Consolidation/holding centre for materials coming to and from site. A

Other Divert construction waste to College for vocational training (BREEAM points).

A

The group then identified the most viable alternative design opportunities to take forward for the quantitative analysis according to the following criteria:

The selected alternative design would reduce the extent of construction site waste by either reducing the

quantity of waste during construction and/or in future repair;

The alternative designs would not increase the project cost, not have a significant negative effect on the

design or construction programme, nor compromise the original design intent; and

The alternative designs selected had the collective buy-in of the design team and were applicable at this stage

of the design process.

After discussion by Davis Langdon and the design team, three ideas were selected for quantitative analysis (Table 3).

Table 3 Ideas selected for quantitative analysis Base design Alternative design

Conventional on site construction of the classrooms. Prefabricated classroom pods.

Cast in-situ concrete columns. Precast concrete columns.

Storage of storm water in a tank. SUDS (geocellular solution).



2.2 Quantitative analysis Three alternative design ideas were selected for quantitative analysis (Table 3). The impact of the changes was quantified by comparing the original design (base design) with the alternative design. A quantitative analysis was undertaken of the potential cost, waste and embodied carbon savings by making this change. The design team and/or specialist subcontractors provided drawings and specifications for each alternative design. The Davis Langdon quantity surveyor was then able to provide the material take off, bill of quantities and unit rates necessary to analyse the potential cost, waste and environmental impact of each design solution. 2.2.1 Calculate The first step in the assessment was to calculate the following factors to inform the analysis:

Total construction cost of design – based on the material composition of the design and unit rates

(including labour, plant and material costs) provided by the quantity surveyor;

Quantity of waste – application of industry material wastage rates (%) to material quantities (m3) summed

to give the volume of waste (m3) arising from the base design and alternative design. Standard conversion

factors applied to convert to mass (tonnes);

Cost of waste disposal – volume of waste (m3) calculated above multiplied by the unit cost of waste

disposal; and

Value of materials wasted – material unit rates (£) multiplied by the volume of waste (m3) to determine

the cost.2 This cost was multiplied by the materials percentage to exclude plant and labour and determine the

value of materials wasted (£);

Total embodied carbon – the sum of the embodied carbon of the materials used for a function in a design

and the embodied carbon of the material waste resulting from that design.3 The savings in the embodied

carbon of waste materials was measured by converting the savings in waste materials (m3) to tonnes of

carbon. The Inventory of Carbon & Energy (ICE)4 developed by researchers at the Department of Mechanical

Engineering, University of Bath was used for the conversion; and5

Number of lorry movements to remove waste from site – based on volume of bulk materials and waste

(m3) to be transported to and from the site in 15 m3 lorries, or other waste materials being collected from site

in 8yd3 (6.1m3) skips.

WRAP’s Net Waste Tool, Guide to Reference Data, Version 1.0 (May 2008)6 was used to source Good Practice wastage rates, rates of disposal and uncompacted bulking factors. The detailed calculations are presented in Appendix A. To estimate the quantity of waste diverted from landfill due to the changes in design, recycling/recovery rates would need to be applied to the quantity of waste arising on site. These rates depend on the site waste management strategy chosen for the site, which is usually not fixed at the design stage of the project. WRAP

2 The value of materials wasted provides a measure of a component of the total construction cost which is spent but does not form a useful function in the finished building. It also represents a measure of unnecessary depletion of finite natural resources which could be avoided by reducing waste through the alternative design change.

3 These are assessed independently as although a reduction in waste from a design change will also reduce the embodied carbon of the waste impact, the alternative design may itself have a higher embodied carbon than the original design. For example, a design manufactured off site may produce less waste than the traditional in situ solution and thus the embodied carbon impact of waste may be less, but it may use materials with a higher embodied carbon or a more carbon intensive manufacturing process.

4 www.bath.ac.uk/mech-eng/sert/embodied/

5 The value of materials wasted accounts for the intrinsic value to society of a further depletion of finite natural resources. A reduction in the value of materials wasted from a design change will avoid the further depletion of finite natural resources.

6 www.wrap.org.uk/nwtool


provides guidance on planning and implementing Good Practice site waste minimisation and management construction projects.7 2.2.2 Compare The second step was to compare for the base design and alternative design of the different ideas on the shortlist:

total construction cost;

quantity of waste created on site;

cost of waste disposal;

total project cost (total construction cost + cost of waste disposal);

number of lorry movements needed to remove waste from site;

value of materials wasted; and

embodied carbon.

The results of the quantitative analysis of the three waste reducing opportunities are summarised in section 3. Following the quantitative analysis, the results were presented to the design team, client and contractor. The team were asked to take on board ideas that could reduce on site waste and be a cost benefit or cost neutral to the project. 3.0 Cost, waste and carbon reductions from selected solutions 3.1 Prefabricated classroom construction The following options were compared for the Southgate College redevelopment project:

Base design: conventional on site construction of classrooms; and

Alternative design: prefabricated classroom pods.

Because there are 33 classrooms of similar specification for the project, the potential impact of the design change is substantial. Modular classrooms involve the prefabrication off site of a unit including walls, roof and floor slab elements. A total of 33 units would be brought to site where they would be craned into place on site. Waste arising from the conventional build solution includes reinforced concrete, precast concrete floor, screed, precast concrete roof, cavity walls, plasterboard, blockwork, polyurethane insulation and plasterboard soffit. The site wastage rate for modular classroom construction was assumed to be zero as waste generated through packaging or transport of materials was not taken into account. Whilst waste would be generated in the factory during the manufacture of the pods, this would be much lower than would be created on site and would also enable high percentage of waste recovery and recycling. Factory waste could not be quantified for this study. Table 4 summarises the savings from opting to use a modular construction over conventional construction. For a full breakdown of the cost, waste and environmental savings see Appendix A. Adopting the modular construction solution would reduce the cost of construction by £52,260 (see Appendix A) and reduce waste disposal costs by £9122, giving a saving in the total project cost of £61,382. Due to virtually no site waste arising from the modular construction, there would be substantial savings in the value of materials wasted (£3956). In addition, the amount of site waste would be reduced by 246 tonnes and approximately 52 lorry movements would be avoided.

7 www.wrap.org.uk/construction/tools_and_guidance/waste_minimisation_and_management/waste_man_guidance.html

Table 4 Cost and waste reductions from using modular classroom construction

Total

project cost

Waste (tonnes)

Embodied carbon of

waste (tonnes) A

No. of lorry movements

B

Cost of waste

disposal

Value of wasted

materials

Conventional classroom construction

£1,716,282 246 46 52 £9122 £3956

Prefabricated classrooms

£1,654,900 0 0 0 £0 £0

Reduction £61,382 246 46 52 £9122 £3956 A: Total of embodied carbon in materials and waste. Does not include carbon impact of the recycling method. B: Based on collections of 8yd3 (6.1m3) skips. 3.2 Precast columns The following two methods of column design were compared across the building for a total of 323 columns:

Base design: conventional cast in situ concrete column; and

Alternative design: precast concrete column.

Table 5 outlines the savings of opting to use precast columns rather than cast in situ columns. A full breakdown of the cost, waste and environment savings can be found in Appendix A. The precast column design has a lower total project cost compared with the cast in situ column design (Table 5). This is primarily due to the lower cost of construction (£157,300 compared with £198,002 – see Appendix A). The precast column design also has a lower cost of waste disposal (£319 instead of £879).

Table 5 Cost and waste reductions from using precast columns

Total

project cost

Waste (tonnes)

Embodied carbon of

waste (tonnes) A


B

Cost of waste

disposal

Value of wasted

materials

Cast in situ columns £198,881 50 27 6 £879 £22,819 Precast columns £157,619 14 3 2 £319 £2288 Reduction £41,262 36 24 4 £560 £20,531

A: Total of embodied carbon in materials and waste. Does not include carbon impact of the recycling method. B: Based on collections of 8yd3 (6.1m3) skips. 3.3 SUDS (geocellular solution) The car park of Southgate College has a large amount of clear surface area which would benefit from installation of geocellular solutions below ground level to act as water collection systems. The following two methods of water collection system were analysed:

Base design: conventional storage of storm water (tank solution); and

Alternative design: sustainable drainage system (SUDS) (geocellular solution).

Table 6 outlines the savings from opting to install SUDS rather than a conventional tank solution. A full breakdown of the cost, waste and environment savings is given in Appendix A.


Table 6 Cost and waste reductions from installing SUDS (geocellular solution)

Total

project cost

Waste (tonnes)

Embodied carbon of

waste (tonnes) A


B

Cost of waste

disposal

Value of wasted

materials

Conventional tank storage

£52,610 335 15 38 £11,742 £1286

SUDS (geocellular solution)

£39,000 0 0 0 £0 £0

Reduction £13,610 335 15 38 £11,742 £0 A: Total of embodied carbon in materials and waste. Does not include carbon impact of the recycling method. B: Based on collections of 8yd3 (6.1m3) skips, and 15 m3 lorry movements for bulk haulage of excavation waste The total project cost for implementing the geocellular water storage solution is significantly lower than the tank solution primarily due to the significant waste savings (virtually no waste arises from the geocellular solution). Waste arising from the tank solution includes excavation works, earthwork support, concrete base and granular fill type one material (see Appendix A for a breakdown of waste arising and costs. 4.0 Discussion 4.1 Potential savings The design team considered three ideas in detail:

prefabricated classroom construction;

precast concrete columns; and

SUDS (geocellular solution).

Table 7 shows the significant benefits to the project of implementing the alternative designs. The total project cost saving is £116,254 of which £21,424 is due to savings in waste disposal costs. In addition there is a saving in the total value of materials wasted of £24,487. Implementing the three design solutions would reduce waste arisings on site by 617 tonnes. This would avoid the need for approximately 94 lorry movements collecting 8yd3 skips and bulk hauling excavation waste. The effect of reduced transport movements from the site was considered an important benefit by the design team as this would reduce both the overall energy consumption of the construction process and local nuisance impacts such as noise and dust. The avoided lorry movements would reduce carbon through reduced transport emissions, although this was not readily quantified. In terms of the impact on embodied carbon associated with the reductions in waste, implementing the three design solutions would reduce this by 85 tonnes.


Table 7 Benefits of the three design solutions

Design solution

Total project cost

A saving

Reduction in waste (tonnes)

Reduction in

embodied carbon of

waste (tonnes) B

Number of lorry

movements avoided

Reduction in cost of

waste disposal

Reduction in value of

wasted materials

Prefabricated classroom construction

£61,382 246 46 52 £9122 £3956

Precast columns

£41,262 36 24 4 £560 £20,531

SUDS (geocellular system)

£13,610 335 15 38 £11,742 £0

Total £116,254 617 85 94 £21,424 £24,487

A: Cost of construction + waste disposal cost B: Does not include carbon impact of transporting waste or recycling/recovery/disposal method. 4.2 Comments on the design solutions 4.2.1 Prefabricated classroom pods The design team identified the following benefits of the prefabricated system:

less on site waste as construction and assembly of modular classrooms is undertaken in a controlled, factory

environment where efficiencies result in less waste (and its better management) and recovery of any waste

which does occur;

enhanced quality of finishes for the final product;

less trade activity (especially wet trades) on site; and

efficiencies in elements of the programme, especially if construction of classrooms delays completion of the

college.

Despite these benefits and the significant cost and waste savings, the design team confirmed that the solution will not be adopted for the Southgate College redevelopment as the design is at an advanced stage making it difficult for this design solution to be implemented. This demonstrates the importance of considering Design for Off Site Construction at an early design stage in projects. The design team members indicated that they would strongly consider adopting this alternative at an early stage of further future projects. 4.2.2 Precast columns A precast column design would be the more efficient method of construction compared with the conventional cast in situ column design as both the programme time and the number of trades required on site is reduced. Precast columns are often cheaper and produce less waste than cast in situ. The cost and waste savings offered by this design solution prompted the design team to consider the opportunities from adopting a steel structural frame. Analysis showed that use of a steel frame would produce further waste savings compared with use of a mixed frame of cast in situ slabs and precast columns. These savings arise because the steel frame is constructed off site and assembled on site, resulting in a low on site wastage rate. The precast column design has a number of benefits compared with the cast in situ column design.

Assuming the frame is on the critical path, the likely time savings could total 1–2 weeks off the project

programme;


The precast columns would be fabricated off site using a timber mould lined with glass reinforced plastic

(GRP). Initial discussions with a potential supplier confirmed that 40 casts could be achieved from one timber

mould; and

It was considered unlikely that formwork for casting in-situ could be used for more than 3–5 castings. The

quantity of formwork could be reduced by approximately 479m2 if the precast solution was adopted.

4.2.3 SUDS (geocellular solution) The sustainable drainage system (geocellular solution) would be the more efficient method of construction compared with the traditional water storage (tank solution) design. The analysis showed that the geocellular solution would have the lower cost and generate less waste.


Appendix A Quantitative analysis results All material unit rates are taken from SPON’S Architects’ and Builders’ Price Book, 134th edition, 2009. All wastage rates are taken from Net Waste Tool, Guide to Reference Data, Version 1.0, May 2008. Rates of disposal and uncompacted bulking factors are also taken from Net Waste Tool, Guide to Reference Data, Version 1.0, May 2008. Unit costs of waste disposal are given for an 8yd3 skip (6.1m3). The cost of waste disposal is based upon segregated skip strategy rates of disposal and uncompacted bulking factors applied to the quantity of waste (m3) calculated These bulking factors account for the amount of air in the skip. For example, given plasterboard waste of 10m3 and a bulking factor of 0.65, this would mean 65% of the skip is air. Thus to determine the volume of plasterboard waste with bulking factors, it is necessary to divide 10m3 by 0.35 (100 – 65 = 35) to give 28.6m3 of plasterboard waste with bulking. Prefabricated classroom construction The analysis compared the construction of 33 classrooms for the following options:

Base design: conventional on site construction of classrooms; and

Alternative design: prefabricated classroom pods.

Conventional on site construction The base method of construction involves quantities and estimates for the frame, floor, roof, external and internal walls, internal finishes, and mechanical and electrical (M&E) services. These values are then increased pro rata for the total of 33 classrooms. Davis Langdon suggested that traditional classrooms for a college or a school would cost £980–1470/m2. For this exercise it was appropriate to use the lowest cost such that the best case scenario for the base design is being compared to the worse case scenario for the alternative design.

Table A1 Base design – cost of construction

Material Area of 33 classrooms

(m2)

Cost to design, manufacture and install

(£/m2)

Total LP&M A cost (£)

LP&M for traditional classroom construction 1742 980 1,707,160

Total cost of construction 1,707,160 A: LP&M = labour, plant and materials

Table A2 Base design – value of materials wasted

Material Volume of

material (m3)

Material unit rate (£/unit)

Wastage rate (%)

Value of materials wasted

(exc. P&L) (£)

Frame Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 400mm 400mm

Concrete 0.96 90.00 4 3.46 Steel reinforcement bars 0.03 340.00 10 1.04 Formwork; 12mm ply 0.03 13.00 100 0.37 Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 450mm 450mm

Concrete 0.61 90.00 4 2.20 Steel reinforcement bars 0.02 340.00 10 0.65 Formwork; 12mm ply 0.02 13.00 100 0.21


Reinforced concrete beams; including formwork and reinforcement at 250kg/m3; 300mm x 600mm

Concrete 8.91 85.00 4 30.29 Steel reinforcement bars 0.28 340.00 10 9.66 Formwork; 12mm ply 0.27 8.00 100 2.14 Floor Precast concrete floor and screed; 350mm thick Precast concrete floor; 350mm thick 88.73 38.00 2 67.43 Floor screed to the above; 100mm 25.35 17.00 5 21.55 Roof Precast concrete roof; 300mm thick 76.05 38.25 2 58.18 External walls External cavity walls; 450mm thick 3mm plaster skim 0.34 2.52 5 0.04 12.5mm plasterboard (nominal 8kg/m2) on dabs on cement sand render

1.41 7.77 22.5 2.46

140mm blockwork 7-20N/mm2 (approx. 1800kg/m3) 15.75 13.58 20 42.78 100mm polyurethane insulation 11.25 12.00 15 20.25 50mm unventilated cavity 5.63 0.30 / / 102mm facing brick 11.48 19.83 20 45.51 Internal walls Internal block walls; 110mm thick 25.25 19.00 20 95.96 12.5mm plasterboard on dabs 0.57 8.00 22.5 1.03 Internal finishes Raised floor (proprietary system) 100.86 28.00 / / Plasterboard soffit; 12.5mm 3.09 24.00 22.5 16.71 Mechanical services 22.00 – Electrical services 16.00 – Total for four classrooms 422 Total for 33 classrooms 3481 Internal doors Solid core, single doorsets / 480.00 3.00 475.20 Total for 33 classrooms 475 Grand total 3956


Table A3 Base design – cost of waste disposal

Material Waste

generated (m3)

Volume waste with

bulking factor (m3)

Cost of disposal (£/m3)

Total cost of waste disposal

(£) Frame Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 400mm 400mm

Concrete (m3) 0.04 0.08 28 2.14 Steel reinforcement bars (t) 0.0031 0.01 – – Formwork; 12mm ply (m2) 0.03 0.06 18 1.02 Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 450mm 450mm (m3)

Concrete (m3) 0.02 0.05 28 1.36 Steel reinforcement bars (t) 0.0019 0.00 – – Formwork; 12mm ply (m2) 0.02 0.03 18 0.57 Reinforced concrete beams; including formwork and reinforcement at 250kg/m3; 300mm 600mm (m3)

Concrete (m3) 0.36 0.71 28 19.86 Steel reinforcement bars (t) 0.0284 0.06 – – Formwork; 12mm ply (m2) 0.27 0.53 18 9.47 Floor Precast concrete floor and screed; 350mm thick (m2) Precast concrete floor; 350mm thick (m2) 1.77 3.55 36 126.83 Floor screed to the above; 100mm (m2) 1.2675 2.54 28 70.65 Roof Precast concrete roof; 300mm thick (m2) 1.5210 3.04 36 108.71 External walls External cavity walls; 450mm thick (m2) 3mm plaster skim (m2) 0.02 0.03 36 1.21 12.5mm plasterboard (nominal 8kg/m2) on dabs on cement sand render (m2)

0.32 0.90 17 14.97

140mm blockwork 7-20N/mm2 (approx. 1800kg/m3) (m2)

3.15 6.30 28 175.57

100mm polyurethane insulation (m2) 1.69 3.38 36 120.61 50mm unventilated cavity (m2) / / / – 102mm facing brick (m2) 2.30 4.59 28 127.92 Internal walls Internal block walls; 110mm thick (m2) 5.05 10.10 28 281.51 2.5mm plasterboard on dabs (m2) 0.13 0.37 17 6.11 Internal finishes Raised floor (proprietary system) (m2) / / / – Plasterboard soffit; 12.5mm (m2) 0.70 1.99 17 32.93 Mechanical services (m2) – – – Electrical services (m2) – – – Total for four classrooms 38 1,101 Total for 33 classrooms 316 9,087 Internal doors Solid core, single doorsets 1 1.98 108.00 35.06 Fittings Whiteboard / / / – Smartboard / / / – Pinboard / / / – Total for 33 classrooms 2 35 Grand total 318 9,122


Table A4 Base design – total quantity of waste

Material Volume of material

(m3)

Wastage rate (%)

Waste generated

(m3)

Tonnes of

waste Frame Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 400mm 400mm

Concrete (m3) 0.96 4 0.04 0.09 Steel reinforcement bars (tonnes) 0.03 10 0.0031 0.02 Formwork; 12mm ply (m2) 0.03 100 0.03 0.02 Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 450mm 450mm (m3)

Concrete (m3) 0.61 4 0.02 0.06 Steel reinforcement bars (tonnes) 0.02 10 0.0019 0.02 Formwork; 12mm ply (m2) 0.02 100 0.02 0.01 Reinforced concrete beams; including formwork and reinforcement at 250kg/m3; 300mm 600mm (m3)

Concrete (m3) 8.91 4 0.36 0.86 Steel reinforcement bars (tonnes) 0.28 10 0.0284 0.22 Formwork; 12mm ply (m2) 0.27 100 0.27 0.19 Floor Precast concrete floor and screed; 350mm thick (m2) Precast concrete floor; 350mm thick (m2) 88.73 2 1.77 4.79 Floor screed to the above; 100mm (m2) 25.35 5 1.2675 1.90 Roof Precast concrete roof; 300mm thick (m2) 76.05 2 1.5210 4.11 External walls External cavity walls; 450mm thick (m2) 3mm plaster skim (m2) 0.34 5 0.02 0.02 12.5mm plasterboard (nominal 8kg/m2) on dabs on cement sand render (m2)

1.41 22.5 0.32 0.19

140mm blockwork 7-20N/mm2 (approx. 1800kg/m3) (m2) 15.75 20 3.15 5.67 100mm polyurethane insulation (m2) 11.25 15 1.69 0.05 50mm unventilated cavity (m2) 5.63 / / / 102mm facing brick (m2) 11.48 20 2.30 3.90 Internal walls Internal block walls; 110mm thick (m2) 25.25 20 5.05 7.07 2.5mm plasterboard on dabs (m2) 0.57 22.5 0.13 0.08 Internal finishes Raised floor (proprietary system) (m2) 100.86 / / / Plasterboard soffit; 12.5mm (m2) 3.09 22.5 0.70 0.42 Mechanical services (m2) – – Electrical services (m2) – – 4Nr. Classrooms: 30 Total for 33 classrooms 245 Internal doors Solid core, single doorsets / 3.00 1 0.80 Fittings Whiteboard / / / / Smartboard / / / / Pinboard / / / / Total for 33 classrooms 1 Grand total 246


Table A5 Base design – volume of waste being transported

Material Waste generated

(m3)

Volume waste with bulking factor (m3)

Frame Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 400mm x 400mm

Concrete (m3) 0.04 0.08 Steel reinforcement bars (t) 0.0031 0.01 Formwork; 12mm ply (m2) 0.03 0.06 Reinforced concrete columns; including formwork and reinforcement at 250kg/m3; 450mm x 450mm (m3)

Concrete (m3) 0.02 0.05 Steel reinforcement bars (t) 0.0019 0.00 Formwork; 12mm ply (m2) 0.02 0.03 Reinforced concrete beams; including formwork and reinforcement at 250kg/m3; 300mm x 600mm (m3)

Concrete (m3) 0.36 0.71 Steel reinforcement bars (t) 0.0284 0.06 Formwork; 12mm ply (m2) 0.27 0.53 Floor Precast concrete floor and screed; 350mm thick (m2) Precast concrete floor; 350mm thick (m2) 1.77 3.55 Floor screed to the above; 100mm (m2) 1.2675 2.54 Roof Precast concrete roof; 300mm thick (m2) 1.5210 3.04 External walls External cavity walls; 450mm thick (m2) 3mm plaster skim (m2) 0.02 0.03 12.5mm plasterboard (nominal 8kg/m2) on dabs on cement sand render (m2)

0.32 0.90

140mm blockwork 7-20N/mm2 (approx. 1800kg/m3) (m2) 3.15 6.30 100mm polyurethane insulation (m2) 1.69 3.38 50mm unventilated cavity (m2) / / 102mm facing brick (m2) 2.30 4.59 Internal walls Internal block walls; 110mm thick (m2) 5.05 10.10 2.5mm plasterboard on dabs (m2) 0.13 0.37 Internal finishes Raised floor (proprietary system) (m2) / / Plasterboard soffit; 12.5mm (m2) 0.70 1.99 Mechanical services (m2) – – Electrical services (m2) – – 4Nr. Classrooms: 38 Total for 33 classrooms 316 Internal doors Solid core, single doorsets 1 1.98 Total for 33 classrooms 2 Grand total 318


Table A6 Base design – Embodied carbon in waste

Material Tonnes of waste

Bath ICE v1.6 carbon rate kgCO2/kg of

material

Carbon equivalent (tonnes)

Concrete 0.0922 0.16 0.015 Steel reinforcement bars 0.0240 1.71 0.041 Formwork, 12mm ply 0.0202 0.81 0.016 Concrete 0.0586 0.16 0.009 Steel reinforcement bars 0.0150 1.71 0.026 Formwork, 12mm ply 0.0113 0.81 0.009 Concrete 0.8554 0.16 0.136 Steel reinforcement bars 0.2230 1.71 0.381 Formwork, 12mm ply 0.1871 0.81 0.152 Precast concrete floor, 350mm thick 4.7912 0.25 1.198 Floor screed to the above, 100mm 1.9013 0.14 0.266 Precast concrete roof, 300mm thick 4.1067 0.25 1.027 3mm plaster skim 0.0219 0.12 0.003 12.5mm plasterboard (nominal 8kg/m2) on dabs on cement sand render 0.1898 0.38 0.072

140mm blockwork 7-20N/mm2 (approx. 1800kg/m3) 5.6700 0.08 0.454

100mm polyurethane insulation 0.0506 3.00 0.152 102mm facing brick 3.9015 0.22 0.858 Internal block walls, 110mm thick 7.0708 0.07 0.523 2.5mm plasterboard on dabs 0.0775 0.38 0.029 Plasterboard soffit, 12.5mm 0.4177 0.38 0.159 Solid core, single doorsets 0.8019 1.24 0.994 Total tonnes of carbon 46

Total cost of construction = £1,707,160

Total cost of waste disposal = £9122

Total value of materials wasted = £3956

Total quantity of materials wasted = 246 tonnes

Total project cost = £1,716,282 (construction cost of £1,707,160 plus cost of waste disposal of £9122)

Embodied carbon in waste = 46 tonnes

Number of lorry movements to transport waste off site in 8yd3 (6.1m3) skips = 52

Prefabricated classrooms This solution involves each classroom unit being constructed off site. The manufacturer provided a range in costs to construct a modular classroom unit and this varied between £850/m2 and £950/m2 depending upon the level of detailing and quantity of items installed. Modular classrooms involve prefabrication off site of a unit consisting of walls, roof and floor slab elements. A total of 33 units would be brought to site and craned into place. The quantity and estimates for this type of construction is a like-for-like comparison for high level traditional build classrooms. The worst case scenario of £950/m2 to design, manufacture and install was taken. Since this method of construction involves prefabrication off site, it is assumed that no wastage occurs on site. Total cost of construction = £1,654,900 (Table A7). The total project cost is also as the cost of waste disposal is zero.


Table A7 Alternative design – cost of construction

Material Area of

classroom (m2) Cost to design, manufacture

and install (£/m2) Total LP&M cost (£)

Modular classroom 1742 950 1,654,900 Total cost of construction 1,654,900 Precast columns versus cast in situ The analysis compared:

Base design: conventional cast in situ concrete column; and

Alternative design: precast concrete column.

Cast in situ column design This base method of construction involves quantities and estimates for C35 in situ concrete, formwork and reinforcement for a total of 323 columns.


Material Total

quantity of materials

Volume of material

(m3)

LP&M unit rate (£/unit)


Total LP&M cost (£)

In situ concrete; C35-20mm aggregate; to structural columns (m3)

286 286.00 168.00 96.00 48,048

Formwork for in situ concrete; columns; basic finish; regular shaped; rectangular or square; height to soffit 3.75m (m2)

2273 6.82 49.50 8.50 112,515

Reinforcement for in situ concrete; bars; BS 4449; hot rolled deformed high steel bars; grade 500C (t)

32 4.08 1170.00 750.00 37,440

Total for in situ column design

198,002

Table A9 Base design – cost of materials wasted

Material Total quantity of material


Wastage rate (%)

Waste generated

(unit)

Value of materials

wasted (exc. P&L) (£)

In situ concrete; C35-20mm aggregate; to structural columns (m3)

286 96.00 4 11 1098

Formwork for in situ concrete; columns; basic finish; regular shaped; rectangular or square; height to soffit 3.75m (m2)

2273 8.50 100 2273 19,321

Reinforcement for in situ concrete; bars; BS 4449; hot rolled deformed high steel bars; grade 500C (t)

32 750.00 10 3 2400

Total for in situ column design

22,819




(unit)



Total cost of waste

disposal (£) In situ concrete; C35-20mm aggregate; to structural columns

11 22.88 28 637.64

Formwork for in situ concrete; columns; basic finish; regular shaped; rectangular or square; height to soffit 3.75m

2273 13.64 18 241.46

Reinforcement for in situ concrete; bars; BS 4449; hot rolled deformed high steel bars; grade 500C

3 0.817 – –

Total for in situ column design 37 879

Table A11 Base design – total amount of waste


(unit) Tonnes of

waste In situ concrete; C35-20mm aggregate; to structural columns 11 27.46 Formwork for in situ concrete; columns; basic finish; regular shaped; rectangular or square; height to soffit 3.75m 2273 19.09 Reinforcement for in situ concrete; bars; BS 4449; hot rolled deformed high steel bars; grade 500C 3 3.20 Total for in situ column design 50




material


In situ concrete, C35 -20mm aggregate, to structural columns 27.46 0.21 5.738

Formwork for in situ concrete, columns, basic finish, regular shaped, rectangular or square, height to soffit 3.75m

19.09 0.81 15.465

Reinforcement for in situ concrete, bars, BS 4449, hot rolled deformed high steel bars, grade 500C

3.20 1.71 5.472

Total tonnes of carbon 27

Total cost of construction = £198,002

Total cost of waste disposal = £879

Total value of materials wasted = £22,819

Total quantity of materials wasted = 50 tonnes

Total project cost = £198,881 (construction cost of £198,002 plus cost of waste disposal of £879).



Precast column design This method of construction involves a total of 323 columns designed on the project.


The quantity and estimates for this type of construction is a like-for-like comparison to the in situ reinforced concrete column design. Advice from Trent Concrete on using precast columns in the design assumes a pin connection for the precast solution to match the quantities detailed in the in situ solution. The precast solution would be fabricated off site within a glass reinforced plastic (GRP) lined, timber mould. Initial discussions with Trent Concrete confirmed that 40 casts from one timber mould could be achieved off site. This compares with the 3–5 casts from one set of formers for the in situ columns – a significant reduction in the amount of formwork required for this solution. The formwork area would be reduced as in situ concrete surface area required is 2273m2, with 760m2 of column formwork likely to be required on site compared with similar surface area for precast concrete columns (2273m2), with a reduction to 282m2 of column formwork instead likely to be required in the factory. Assuming the frame is on the critical path, the likely time saving could total 1–2 weeks off the project programme, reducing the total project construction cost. Precast column construction would cost £550 per column for a total of 323 columns. The wastage rate is 2%.

Table A13 Alternative design - cost of construction


(m3) LP&M unit rate

(£/unit) Total LP&M cost

(£) Installation 286 550 157,300 Total for precast column design 157,300

Table A14 Alternative design – value of materials wasted


(m3)

Wastage rate (%)

Waste generated

(unit)

Value of materials wasted (exc.

P&L) (£) Installation (m3) 286 2 6 2288 Total for precast column design 2288

Table A15 Alternative design – cost of waste disposal

Material Waste

generated (unit)



Total cost of waste

disposal (£) Installation (m3) 6 11.44 28 318.82 Total for precast column design 11 319

Table A16 Alternative design – total quantity of waste


(unit) Volume waste with bulking factor (m3)

Tonnes of waste

Installation (m3) 6 11.44 13.73 Total for precast column design 11 14

Table A17 Alternative design – Embodied carbon in waste



material


Installation 13.73 0.25 3.432 Total tonnes of carbon 3


Total cost of construction = £157,300 (Table A13).

Total cost of waste disposal = £319 (Table A15).

Total value of materials wasted = £2288 (Table A14).

Total quantity of materials wasted = 14 tonnes (Table A16).

Total project cost = £157,619 (construction cost of £157,300 plus cost of waste disposal of £319).



SUDS versus tank storage of storm water Tank storage This base method of construction involves the quantities and estimates for installing water tank solutions at the Southgate College project. The following calculations were based on a tank solution with an attenuation of 60,000 litres of storm water.


Material Total

quantity of material

LP&M unit rate

(£/unit)


Total LP&M cost (£)

Excavation for tank; depth not exceeding 4m (m3) 216 12.50 6.50 2700.00 Earthwork support (close boarded); maximum depth 4m; distance between faces 2–4m (m2) 160 19.50 3.00 3120.00 Dispose of arisings; off site to tip; inactive non hazardous waste; including landfill tax (m3) 216 20.00 – 4320.00 Tank base, concrete bed (m3) 14.40 120.00 96.00 1728.00 Corrugated steel pipe; 2.2m diameter; supply and install (m) 24 1000 600.00 24,000.00 Filling to make up levels; obtained off site; granular fill type one (m3) 125 40.00 37.00 5000.00 Total for traditional tank solution 40,868

Table A19 Base design – value of materials wasted

Material Total

quantity of material

Wastage rate (%)

Waste generated

(unit)

Value of materials wasted

(exc. P&L) (£)

Excavation for tank; depth not exceeding 4m (m3) 216 / / / Earthwork support (close boarded); maximum depth 4m; distance between faces 2–4m (m2) 160 10 16 48.00 Dispose of arisings; off site to tip; inactive non hazardous waste; including landfill tax (m3) 216 / / / Tank base, concrete bed (m3) 14.40 4 0.57600 55.30 Corrugated steel pipe; 2.2m diameter; supply and install (m) 24 5 0.28566 720.00 Filling to make up levels; obtained off site; granular fill type one (m3) 125 10 13 462.50 Total for traditional tank solution 1286



Material Waste

generated (unit)

Volume waste with

bulking factor (m3)


Total cost of waste

disposal (£)

Excavation for tank; depth not exceeding 4m (m3)

/ / / –

Earthwork support (close boarded); maximum depth 4m; distance between faces 2–4m (m2)

16 32.00 £18 566.56

Dispose of arisings; off site to tip; inactive non hazardous waste; including landfill tax (m3)

216 432 £24 A 10,447.06

Tank base, concrete bed (m3) 0.57600 1.15 £28 32.10 Corrugated steel pipe; 2.2m diameter; supply and install (m)

0.28566 0.57 / –

Filling to make up levels; obtained off site; granular fill type one (m3)

13 25.00 £28 696.72

Total for traditional tank solution 491 11,742 A: 20yd3 (15.3m3) lorry bulk haulage

Table A21 Base design – total quantity materials wasted


(unit) Tonnes of

waste Excavation for tank; depth not exceeding 4m (m3) / / Earthwork support (close boarded); maximum depth 4m; distance between faces 2–4m (m2)

16 11.20

Dispose of arisings; off site to tip; inactive non hazardous waste; including landfill tax (m3)

216 302.40

Tank base, concrete bed (m3) 0.57600 1.38 Corrugated steel pipe; 2.2m diameter; supply and install (m) 0.28566 2.24 Filling to make up levels; obtained off site; granular fill type one (m3) 13 17.50 Total for traditional tank solution 335




material


Earthwork support (close boarded), maximum depth 4m, distance between faces 2–4m

11.20 0.81 9.072

Tank base, concrete bed 1.38 0.25 0.346 Corrugated steel pipe, 2.2m diameter, supply and install 2.24 2.51 5.629

Filling to make up levels, obtained off site, granular fill type one 17.50 0.01 0.088

Total tonnes of carbon 15

Total cost of construction = £40,868

Total cost of waste disposal = £11,742

Total quantity of waste = 335 tonnes

Total value of material wasted = £1286



Total project cost = £52,610 (construction cost of £40,868 plus cost of waste disposal of £11,742)


Number of lorry movements to transport waste off site in 8yd3 (6.1m3) skips and 20yd3 (15.3m3) lorries for

bulk haul = 38

SUDS (geocellular solution) This solution is based on a 300mm depth solution, applying a 2/3 rule for attenuation volume. The low lying car park area on the Southgate College site is an appropriate location for the geocellular system to be used as a sufficient amount of area is available at the level required. This method of attenuation is appropriate as its land take is minimal and in general it can be designed to suit most sites. It is assumed that there is no wastage. The total project cost is the same as the total cost of construction of £39,000 (Table A22) as the cost of waste disposal is zero.

Table A23 Alternative design – cost of construction

Material Total quantity

of material Volume of

material (m3) LP&M unit rate

(£/unit) Total LP&M

cost (£) Installation (m2) 300 90 130 39,000 Total 39,000

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