Case study: Designing out Waste Colchester and Chelmsford ... and Chelmsford Courts... ·...

Case study: Designing out Waste

Colchester and Chelmsford Magistrates’ Courts

A design review of the project to build new magistrates’ courts in Colchester and Chelmsford identified easy to implement ideas to reduce construction waste with the potential to reduce total project costs by £166,625, reduce the amount of waste produced on site by 2160 tonnes and avoid 159 lorry movements.

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 [Aedas] 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 Aedas Architects to demonstrate these principles in practice by identifying cost-effective and feasible waste reducing opportunities in the design of two new magistrates’ court buildings in Colchester and Chelmsford for Her Majesty’s Court Service. 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. Four of these ideas were selected as being the most appropriate for quantitative analysis:

prefabricated reinforced concrete staircases instead of in situ conventional construction;

post-tension flat slabs instead of in situ ribbed slab construction;

use of two types and quantities of replacement piles; and

recycling of excavated car park material for use in the piling mat.

A comparative assessment of these four 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 four design solutions. Implementing the four alternative designs would:

reduce total project costs by £166,625;

reduce waste arisings on site by 2610 tonnes;

avoid 159 lorry movements;

reduce waste disposal costs by £28,118; and

reduce the value of materials wasted by £13,267.

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

Colchester and Chelmsford Magistrates’ Courts 1


Results of quantitative analysis of design solutions for the Colchester and Chelmsford magistrates’ courts project

Design solution

Total project cost A saving

Waste reduction (tonnes)

Number of lorry movements

avoided

Reduction in waste

disposal costs

Reduction in value of wasted

materials Prefabricated concrete staircases

£18,748 28 9 C £924 £12,558

Post-tensioned flat slabs

£70,093 (7) E – £1320 £709

CFA replacement piles

£34,854 681 23 D £6794 N/A

Retention of excavated material B

£42,930 1908 127 D £19,080 N/A

Total £166,625 2610 159 £28,118 £13,267

A: Cost of construction + waste disposal cost B: Colchester site only C: Based on collections of 8yd3 (6.1m3) skips D: Based on 15 m3 lorry movements E: Although waste tonnage increases, waste volume reduces by 8m3.

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

1.1 .......................................................................................................5 The construction scheme1.2 ...................................................................................................................5 The project team

2.0 ................................................................................................... 5 Designing out Waste process2.1 ........................................................................................................5 Design review workshop

2.1.1 ....................................................................................................6 Awareness session2.1.2 ......................................................................................................6 Creativity session2.1.3 .....................................................................................................6 Reasoning session

2.2 ..............................................................................................................9 Quantitative analysis2.2.1 ..................................................................................................................9 Calculate2.2.2 ................................................................................................................10 Compare

3.0 ....................................................... 10 Cost, waste and carbon savings from selected solutions3.1 ................................................................................................10 Prefabricated concrete stairs3.2 .............................................................................................................11 Post-tensioned slab3.3 ..............................................................................................................12 Replacement piling3.4 ..................................................................13 Retain car park excavation material as piling mat

4.0 .............................................................................................................................. 14 Discussion4.1 .................................................................................................................14 Potential savings4.2 .......................................................................................14 Comments on the design solutions

4.2.1 .............................................................................14 Prefabricated concrete staircases4.2.2 ...............................................................................................15 Post-tension flat slab4.2.3 ......................................................15 Retain car park excavation material as piling mat

Appendix A Quantitative analysis results........................................................................................... 16 Prefabricated concrete stairs versus cast in situ concrete stairs ...........................................................16 Post-tensioned flat concrete slab versus conventional reinforced concrete slab ....................................19 CFA replacement piles ......................................................................................................................27 Retain excavation material as piling mat versus dispose and import aggregate ....................................29



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 Aedas Architects to identify and investigate opportunities for Designing out Waste on the Colchester and Chelmsford magistrates’ courts project for Her Majesty’s Court Service.

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

1.1 The construction scheme Her Majesty’s Court Service (HMCS) is currently developing two new magistrates’ courts buildings, with a very similar design, in inner city locations in Chelmsford and Colchester. The court buildings are being developed together as a scheme with Aedas Architects and Mott MacDonald as lead consultant. The project is being procured using a single stage Design & Build contract and a single contractor will deliver both projects. The estimated construction value of the project is approximately £30 million. Both buildings follow similar design layouts in compliance with the HMCS Court Standards and Design Guide Magistrates (published 2007). The layout includes secured and defined areas (including staircases) for custodial, public, magistrates’/staff, jury, judiciary and barristers/solicitors. Both building structures are of reinforced concrete frame and floor slab construction. Cladding consists of a combination of metal, glazed, solid and obscured panels. Colchester has three floors with a first floor mezzanine. Chelmsford is two floors with first floor and second floor mezzanines. Both sites are currently car parks in a central location close to public transport; HMCS owns both sites. Chelmsford Magistrates’ Court already has outline planning permission and detailed planning applications will be submitted at the same time as the appointment of the contractor. Both projects are at the end of RIBA Stage C, early Stage D design. The client’s aspirations for this project are:

design excellence;

sustainability – compliance with Section 26, HMCS Court Standards and Design Guide;

BREEAM ‘Excellent’ rating; and

10–15% renewable energy generation (Section 106 Agreement under the Town and Country Planning Act

1990).

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:

HMCS (client);

Aedas Ltd (architects);

Mott MacDonald (lead consultants, structures, mechanical and electrical);

Franklin + Andrews (quantity surveyor); and

contractor – to be appointed (at the time of writing).

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 22 October 2008 at Aedas Architects’ offices in London. It was attended by:

Nadja Wloka, Project Architect Chelmsford Magistrates’ Court, Aedas Architects Ltd;


Pamela Sindram, Project Architect Colchester Magistrates’ Court, Aedas Architects Ltd;

Judit Kimpian, Head of Sustainability, Aedas Architects Ltd;

Joshua Ogier, Design Team Leader, Mott MacDonald, Cambridge;

David Bailey, Structural Engineer, Mott MacDonald, Cambridge;

Trevor Bishop, Mechanical Engineer, Mott MacDonald, Cambridge;

Derek Millington, Principal Quantity Surveyor, Franklin + Andrews;

Nora Popescu-Kirby, Senior Consultant, Davis Langdon; and

Edwina McKechnie, Consultant, Davis Langdon.

The workshop had three separate but consecutive sessions:

Awareness session – review of Designing out Waste principles, and a 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 Colchester and Chelmsford magistrates’ courts 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

Use similar designs/materials in both projects so waste in one project can be used for the other (lagged programme between the two). Recycle car park material as fill. Wire cages parking lot as sustainable drainage system (SUDS). (A–C) Blockwork instead of plasterboard (more structural load and foundations). (A–B)

Design for Reuse and Recovery

Omitting plasterboard or dry lining in build (internal). Off site cladding panels – reuse waste in factory, reduced weight and therefore materials in foundations. Prefabricated stairs. Prefabricated stair wells. Thermodeck off site precast concrete structure.

Design for Off Site Construction

Modular design. Post-tension flat slabs to minimise slab depth, flat soffit, partitions and formwork. Also implications for deconstruction. Piled foundations – rotary system to reduce the amount of spoil to be reduced. Modular shuttering for concrete. Precut wall elements and delivered with doors and clip into place. (A–B)

Design for Materials Optimisation

Prefabricated core with mechanical and electrical (M&E) openings. Employ a specialist/’sympathetic’ waste specialist for removing/dealing with waste. Contractual documents to specify review of contractor’s supply chain at contractor selection. Create a financial incentive for the contractor to reduce and recycle waste. Talk to suppliers of wall lining systems about opportunities to reduce material waste. Method statements from contractors to reduce waste on site and for correct installation of fragile materials. Dialogue with plasterboard manufacturer.

Design for Waste Efficient Procurement

Architects to specify responsibly sourced materials. (A–B) Find out what waste current products produce when deconstructed. Brickwork and mortar to be recyclable. (A–B) Recycle car park cover material/demolition product.

Design for Deconstruction and Flexibility

Consider reuse potential once design life complete. ‘B’ – High impact on waste reduction, difficult to implement Design for Reuse and Packaging to be reused as part of public art installation (e.g. elephant in Rowan


House) or kitchen worktops. Recycle car park cover material for internal floor finish in Colchester (quality constraints). Site strip/enabling works waste to be reused. Cavity fill with asphalt. Remelt tarmac and pour into moulds for landscaping and waterproofing. (B-D)

Recovery

Use all waste products as cladding materials. Create module for walls and windows to reduce cut offs especially in dry walls. Consider construction / manufacturing procedures to eliminate/reduce waste. Revisit model to schedule plasterboard, insulation. Revisit model to check for pipe lengths, clasps.


Time construction and delivery through three-dimensional (3D) model; locate and plan storage for exact quantities.

Design for Waste Efficient Procurement

Client buy in when it comes to construction input (e.g. ATOS/SERCO), involve third parties Prefabricated elements should be taken away, detailing? Design for

Deconstruction and Flexibility

‘Best fit’ material selection (not too large selection – stone, etc), broken down and reused at later date.

‘C’ – Low impact on waste reduction, easy to implement Design for Reuse and Recovery

Custody area block work – use recycled blocks.


Concrete core shuttering and standard modular openings.

Source materials locally – more likely to recycle and less fuel ‘waste’ in delivery. Design for Waste Efficient Procurement Recyclable fuels – biomass is itself renewable. Other Consider insulation quantities in order to reduction heating/energy requirements. ‘D’ – Low impact on waste reduction, difficult to implement Design for Reuse and Recovery

Remelt tarmac and pour into moulds for landscaping and water proofing. (B–D)

Design for Off Site Construction

Use prefabricated timber construction instead of concrete (thermal mass issue).

Ensure sizing of services of materials is as accurate as possible, less material used (programme issues).


Co-ordination of stairways. Design for Waste Efficient Procurement

M&E on time.

Design for Deconstruction and Flexibility

Screw fix where possible for better deconstruction.

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.

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

Recycle car park material as fill. A Design for Reuse and Recovery Recycle car park material in wire cages as SUDS. A–C

Off site cladding panels. A Design for Off Site Construction Prefabricated stairs. A

Post-tensions flat slabs to minimise slab depth, flat soffit, partitions and formwork.

A

Rotary piles. A Modular shuttering for concrete. A


Precut wall elements delivered with doors to be clipped into place. A–B Design for Waste Efficient Procurement

Method statements from contractors to reduce waste on site and for correct installation.

A

Brickwork and mortar to be recyclable. A–B Design for Deconstruction and Flexibility Recycle car park cover/demolition product. A After discussion by Davis Langdon and the design team, four ideas were selected for quantitative analysis (Table 3).

Table 3 Ideas selected for quantitative analysis Base design Alternative design

Cast in situ concrete stairs. Prefabricated concrete stairs.

Conventional reinforced ribbed slab construction. Post-tensioned flat slab construction.

Conventional continuous flight auger (CFA) piles. Displacement flight auger (FA) piles.

Disposal of all excavated car park material and import of new materials for piling mat.

Recycling of excavated car park material in piling mat.

2.2 Quantitative analysis Four 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 created on site – 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;



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 (£); and

Number of lorry movements to remove waste from site – based on volume of waste (m3) to be

transported, being collected from site in 8yd3 (6.1m3) skips or 15m3 lorries.

WRAP’s Net Waste Tool, Guide to Reference Data, Version 1.0 (May 2008)3 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 provides guidance on planning and implementing Good Practice site waste minimisation and management construction projects.4 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; and

value of materials wasted.

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 savings from selected solutions 3.1 Prefabricated concrete stairs The following options were investigated:

Base design: cast in situ concrete stairs and landings; and

Alternative design: prefabricated stairs and landings.

There are seven staircases of similar specifications in both court buildings to allow for separate and secure circulation areas for custodial, judiciary and public. Table 4 outlines the savings of opting to use a prefabricated system over a conventional cast in situ solution. See Appendix A for a full breakdown of the cost and waste savings. The total project cost for use of prefabricated staircases and landings is lower than that for conventional in situ concrete stair construction. Both the cost of construction and the cost of waste disposal (there is virtually no waste on site with the prefabricated solution) are less with the alternative design. Waste from the base design

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 www.wrap.org.uk/nwtool

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

includes concrete, formwork, plasterboard and reinforcement waste (see Appendix A for a breakdown of waste arising and costs). Adopting the prefabricated solution on both projects would reduce the cost of construction by £17,824 and reduce waste disposal costs by £924, giving a saving in the total project cost of £18,748 (Table 4). Due to virtually no waste with the prefabricated solution, there would also be substantial savings in the value of materials wasted (£12,558). In addition, the amount of waste would be reduced by 28 tonnes and nine lorry movements to transport waste off site in 8yd3 (6.1m3) skips would be avoided.

Table 4 Prefabricated staircases and landings rather than cast in situ – results of quantitative analysis

Construction

cost Waste

(tonnes) Cost of waste

disposal

Value of wasted

materials

Total project cost A

Colchester Magistrates’ Court Cast in situ £50,983 12.25 £462 £6279 £51,445 Prefabricated £43,344 N/A N/A N/A £43,344 Reductions £7639 12.3 £462 £6279 £8101 Chelmsford Magistrates’ Court Cast in situ £67,977 16 £461.9 £6279 £68,439 Prefabricated £57,792 N/A N/A N/A £57,792 Reductions £10,185 16.0 £462 £6279 £10,647 Total project savings

£17,824 28.3 £924 £12,558 £18,748

A: Cost of construction + waste disposal cost 3.2 Post-tensioned slab The following methods of concrete slab construction were compared for the gross floor area over an equivalent of three floors in the Colchester (2293m2) and Chelmsford (2282.6m2) buildings:

Base design: conventional reinforced ribbed slab (600mm depth with 900mm centres); and

Alternative design: post-tensioned flat slab (250–450mm section depth).

A post-tensioned slab has a number of benefits compared with a conventional reinforced ribbed slab including:

less need for reinforcement;

less formwork and shuttering;

a thinner slab resulting in an overall reduction in the height of the building and therefore less cladding; and

coverage of longer spans.

Table 5 outlines the savings from opting to use post-tensioned slabs rather than conventional reinforced slabs. See Appendix A for a full breakdown of the cost and waste savings. The lower total project cost of the post-tensioned slab design is primarily due to the lower cost of construction due to the need for less reinforcement and formwork materials. The cost of waste disposal is also lower with the post-tensioned slab because there is less reinforcement and formwork waste. But the alternative design is estimated to produce more total waste (6.5 tonnes) than the base design. Overall for the project there would be a saving in the value of wasted materials of £709. Use of the post-tensioned construction method in both projects would reduce the cost of construction by £68,773 and reduce waste disposal costs by £1320, giving a saving in the total project cost of £70,093.


Table 5 Post-tensioned slabs rather than conventional reinforced slabs – results of quantitative analysis

Design Construction

cost Waste (m3)

Waste (tonnes)

Cost of waste

disposal

Value of wasted material


Colchester Magistrates’ Court Conventional reinforced slab

£278,144 64 82 £3011 £3268 £281,155

Conventional reinforced slab + extra cladding B

£289,765 70 90.20 £3439 £4247 £293,204

Post-tensioned flat slab £259,805 65 90.60 £2789 £3628 £262,594 Reductions £29,960 5 (0.40) £650 £619 £30,610 Chelmsford Magistrates’ Court Conventional reinforced slab

£416,525 95 123 £4506 £4852 £421,031

Conventional reinforced slab + extra cladding B

£424,911 99.55 128.90 £4814 £5481 £429,725

Post-tensioned flat slab £386,098 97 135 £4144 £5391 £390,242 Reductions £38,813 2.55 (6.10) £670 £90 £39,483 Total project savings £68,773 7.55 (6.50) £1320 £709 £70,093 A: Cost of construction + waste disposal cost B: Extra cladding is required for the conventional reinforced slab compared with the post-tensioned flat slab because the building will be slightly higher due to the greater thickness of the ribbed slab. 3.3 Replacement piling The design review workshop identified the potential to reduce excavation waste by adopting different type of replacement piling. Initially, the design team investigated the benefits of using displacement flight auger (FA) piles instead of continuous flight auger (CFA) piles. It was expected that displacement FA piles would generate no spoil, thus eliminating disposal costs and outweighing any increase in the cost of construction using this technique. However discussions with the specialist contractor indicated that, due to the ground conditions at both sites, the same amount of spoil would be generated with both piling scenarios and thus there would be no benefit in terms of waste arisings from the alternative design. The structural engineer subsequently suggested comparing the use of two CFA replacement piles, which were feasible on both the Colchester and Chelmsford buildings. CFA replacement piling requires drilling of a hollow-stem auger into the ground. Concrete is pumped into the hole as the auger is removed, eliminating the need for temporary casing or slurry. After the auger is removed, reinforcement is installed. The two piling scenarios investigated were as follows:

Base design: one CFA replacement pile, 900mm diameter, per location of column; and

Alternative design: two CFA replacement piles, 600mm diameter, per location of column.

Table 6 outlines the savings from implementing the alternative design at the two sites. See Appendix A for a full breakdown of the cost and waste savings. Using two 600mm diameter CFA piles at each column location on both sites rather than one 900mm diameter CFA pile would reduce the cost of construction by £28,060 and reduce waste disposal costs by £6794, giving a saving in the total project cost of £34,854 (Table 6). In addition, the amount of waste would be reduced by 681 tonnes and 23 lorry (15m3) movements to transport waste off site would be avoided.


Table 6 Double piles rather than single piles – results of quantitative analysis

Construction cost

Waste (tonnes)

Cost of waste disposal


Colchester Magistrates’ Court One 900mm diameter CFA pile £136,500 1612.70 £16,120 £152,620 Two 600mm diameter CFA piles £121,550 1249.76 £12,500 £134,050 Reduction £14,950 362.94 £3620 £18,570 Chelmsford Magistrates’ Court One 900mm diameter CFA pile £119,700 1413.60 £14,136 £133,836 Two 600mm diameter CFA piles £106,590 1096.00 £10,962 £117,552 Reduction £13,110 317.60 £3174 £16,284 Total project savings £28,060 681 £6794 £34,854 A: Cost of construction + waste disposal cost 3.4 Retain car park excavation material as piling mat Base design: disposal of all excavated material and import of aggregate for piling mat; and

Alternative design: retention and recycling of a proportion of the excavated material for use as a piling mat

and disposal of the remaining material.

Both sites are currently car parks which will require excavation during the enabling works. However, the geotechnical survey of the Chelmsford site found the soil properties there to be unsuitable for recycling for use as a piling mat. The assessment therefore focused on the recycling potential at the Colchester site. The total volume of excavated material available on the Colchester site is 1655m3 (based on the required reduction of levels to a depth of 400mm below the existing car park ground level). The piling mat will require 954m3 of material. Table 7 outlines the savings of reusing 954m3 of available excavation material in the piling mat for the Colchester site. See Appendix A for a full breakdown of the cost and waste savings.

Table 7 Retention and recycling of excavation material rather than disposal and import of aggregate – results of quantitative analysis

Colchester Waste

(tonnes)

Total cost excavation

and crushing

Total cost moving

excavated material on

site

Total cost excavation

and disposal

Total cost importing material

Total project cost C

Base design A 3310 £38,065 £33,390 £71,455 Alternative design B 1402 £9540 £2862 £16,123 £28,525 Project savings 1908 £21,942 £42,930A: Excavate and disposal of on site material (1655m3) and import piling mat (954m3). B: Excavate, crush and movement of retained material for piling (954m3) and disposal of remaining (701m3). C: Cost of construction + waste disposal cost. The total project savings from excavating, crushing, moving and reusing 954m3 of excavation material on site and disposing of the remaining 701m3 would be £42,930 (Table 7), of which £19,080 is due to the reduced cost of waste disposal. In addition, the amount of waste would be reduced by 1908 tonnes and 127 lorry (15m3) movements to transport waste off site and aggregate onto site would be avoided.


4.0 Discussion 4.1 Potential savings The design team considered four ideas in detail:

prefabricated concrete staircases;

post-tensioned flat slabs;

different CFA replacement piles; and

retention of excavated material for piling mat.

Table 8 shows the savings for each of the four design solutions. The total project cost saving is £166,625 of which £21,118 is due to savings in waste disposal costs. In addition there is a saving in the total value of materials wasted of £13,267. Implementing the four design solutions would reduce waste arisings on site by 2610 tonnes and avoid the need for approximately 159 lorry movements. The effect of reduced transport movements from the site was considered an important benefit by the design team as this would reduce both direct carbon dioxide emissions and local nuisance impacts such as noise and dust.

Table 8 Benefits of the four design solutions

Design solution

Total project cost A saving

Reduction in waste (tonnes)

Number of lorry movements

avoided

Reduction in cost of waste

disposal

Reduction in value of wasted

materials Prefabricated concrete staircases

£18,748 28 9 C £924 £12,558

Post-tensioned flat slabs

£70,093 (7) E – £1320 £709

CFA replacement piles

£34,854 681 23 D £6794 N/A

Retention of excavated material B

£42,930 1908 127 D £19,080 N/A

Total £166,625 2610 159 £28,118 £13,267

A: Cost of construction + waste disposal cost B: Colchester site only C: Based on collections of 8yd3 (6.1m3) skips. D: Based on 15 m3 lorry movements. E: Although waste tonnage increases, waste volume reduces by 8m3. 4.2 Comments on the design solutions 4.2.1 Prefabricated concrete staircases Because there are seven staircases per building, up to three stories, the potential impact of the design change is substantial. The design team identified the following benefits of the prefabricated system:

less on site waste as construction and assembly of staircases is done in a controlled, factory environment

where efficiencies result in less waste and better management and recovery of any waste that does occur;

enhanced quality of finishes for the final product;

less trade activity (especially wet trades) on site as stairwell construction becomes an assembly process of

parts; and

improved programme efficiency.


4.2.2 Post-tension flat slab Post-tensioned concrete flat slab construction involves pouring concrete around sheaths or ducts containing unstressed tendons. Once the concrete has gained sufficient strength, the tendons are stressed against the concrete and locked off by special anchor grips known as split wedges. In this system, all tendon forces are transmitted directly to the concrete. Since no stresses are applied to the formwork, conventional formwork can be used. However, use of thinner post-tensioned slabs would lead to a reduction in the overall height of the buildings. The height of the building with the conventional reinforced slab solution would therefore mean that a proportional increase in the amount of cladding would be required. When the additional costs and waste associated with extra cladding for the thicker conventional reinforced floor slab are considered, the post-tensioned slab design is the more efficient solution. In addition, a reduction in the overall height of both buildings would also affect the quantity of materials required for supporting columns and staircases (both reinforced concrete), and subsequent waste. Thus, the cost and waste benefits of using a thinner post-tensioned slab and reducing both building heights are an underestimate of what could be achieved in reality. The post-tensioned slab is the lower cost option but has a minimal impact on waste when considering a straightforward comparison between it and the conventional reinforced slab option. This is primarily due to the concrete requirements and subsequent waste from the post-tensioned flat slab. The waste argument for post-tensioned slabs is enhanced when considering the knock-on effects of utilising a thinner slab in terms of reduced cladding, and also reinforced concrete columns and staircases. Thus, the saving in concrete use and subsequent waste by designing for a thinner post-tensioned slab would enhance the cost and waste case for taking this design option further. 4.2.3 Retain car park excavation material as piling mat The programme is phased with work on Chelmsford scheduled to commence ahead of Colchester. There is a substantial amount of suitable excess excavated material available from the Colchester site, so starting the enabling works at Colchester would allow the excavated material to be recycled for use in the piling mat on both sites.


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.

Table A1 Densities used in the calculations Material Density (tonnes/m3) Brickwork 1.7 Copper 8.6 Plywood 0.7 Insulation 0.015 Block work 1.8 Concrete 2.4 Formwork (plywood) 0.7 Reinforcement 7.8 Polypropylene 1.2 Plasterboard 0.6 Prefabricated concrete stairs versus cast in situ concrete stairs The analysis compared the following two methods of construction for both the Colchester and Chelmsford court buildings:

Base design: cast in situ concrete stairs and landings; and

Alternative design: prefabricated stairs and landings.

The calculations below are based on 36 flights of stairs in the Colchester building. The results are then used on a pro rata basis to determine the results for 48 flights of stairs in the Chelmsford building. Cast in situ concrete stairs (Colchester)

Table A2 Breakdown of unit rates and wastage rates for in situ construction of staircases

Material Unit rate Wastage rate

(%) Concrete £186.09/m3 4 H12 reinforcement £1230.84/tonne 10 H16 reinforcement £1147.63/tonne 10 H10 reinforcement £1339.55/tonne 10 Formwork for shuttering £47.04/m2 100 Formwork for risers £120/m2 100 Soffit finishes, taped & jointed plasterboard including soffit, landing and strings

£20/m2 22.5

Soffit finishes, dot and dab including soffit, landing and strings £6/m2 22.5 Screed for landings £14.49/m3 2 Latex cement screed for treads £5.76/m3 2


Table A3 Base design – cost of construction (Colchester) A

Materials Quantity of

material LP&M unit

rate (£) Total LP&M

cost (£) Concrete (m3) 58 186 10,868 Reinforcement (tonnes) H12 main 1 1231 1034 Reinforcement (tonnes) H16 main 0 1148 379 Reinforcement (tonnes) H10 dist 1 1340 911 Formwork/shuttering (m2) 360 47 16,920 Soffit finishes – dot and dab (m2) including soffit, landing and strings

360 6 2158

Soffit finishes – taped & jointed plasterboard (m2) including soffit, landing and strings

360 20 7194

Formwork – riser (m2) 68 120 8207 Screed – 50ml (m2) – landing only 186 14 2697 Latex cement screed – treads only (m2) 107 6 616 Total 50,983 A: Data provided by Davis Langdon.

Table A4 Base design – volume of waste (Colchester)

Quantity of

material

Volume of material

(m3)

Wastage rate (%)

Volume of waste (m3)

Tonnes of waste

Concrete (m3) 58.40 58.40 4 2.34 5.61 Reinforcement (tonnes) H12 main 0.84 0.11 10 0.01 0.08 Reinforcement (tonnes) H16 main 0.33 0.04 10 0.00 0.03 Reinforcement (tonnes) H10 dist 0.68 0.09 10 0.01 0.07 Formwork/shuttering (m2) 359.70 6.47 100 6.47 4.53 Soffit finishes – dot and dab (m2) including soffit, landing and strings

359.70 4.50 22.5 1.01 0.61

Formwork – riser (m2) 68.39 1.23 100 1.23 0.86 Screed – 50ml (m2) – landing only 186.12 9.31 2 0.19 0.45 Latex cement screed – treads only (m2)

106.92 0.53 2 0.01 0.006

Total 1141.08 80.68 11.27 12.25

Table A5 Skip costs and uncompacted bulking factors for different wastes from the base design A

Waste stream Cost of waste disposal per skip Bulking factor of material Inert £170 0.50 Timber £108 0.50 Plasterboard £101 0.65 A: The cost of waste disposal for metal is taken to be zero due to its high resale value.


Table A6 Base design – cost of waste disposal (Colchester)

Material Volume of waste

(m3)

Volume waste with bulking factor (m3)

Cost of disposal per skip (£)

Cost of waste

disposal (£) Concrete (m3) 2.34 4.67 £170 130.20 Reinforcement (tonnes) H12 main 0.01 – – 0.00 Reinforcement (tonnes) H16 main 0.00 – – 0.00 Reinforcement (tonnes) H10 dist 0.01 – – 0.00 Formwork/shuttering (m2) 6.47 12.95 £108 229.26 Soffit finishes – dot and dab (m2) including soffit, landing and strings

1.01 2.89 £101 47.86

Soffit finishes – taped & jointed plasterboard (m2) including soffit, landing and strings

– – 0.00

Formwork – riser (m2) 1.23 2.46 £108 43.59 Screed – 50ml (m2) – landing only 0.19 0.37 £170 10.37 Latex cement screed – treads only (m2)

0.01 0.02 £170 0.60

Total 11.27 23.37 461.89

Table A7 Base design – value of wasted materials (Colchester)

Material Total material cost (£) Wastage rate

(%)

Value of materials wasted

(exc. P&L) Concrete (m3) 5,635.02 4 225.40 Reinforcement (tonnes) H12 main 650.51 10 65.05 Reinforcement (tonnes) H16 main 240.65 10 24.07 Reinforcement (tonnes) H10 dist 574.67 10 57.47 Formwork/shuttering (m2) 2,927.96 100 2927.96 Soffit finishes – dot and dab (m2) including soffit, landing and strings 863.28 22.5 194.24 Soffit finishes – taped & jointed plasterboard (m2) including soffit, landing and strings 1151.04 22.5 258.98 Formwork – riser (m2) 2,462.04 100 2462.04 Screed – 50ml (m2) – landing only 2,696.88 2 53.94 Latex cement screed – treads only (m2) 492.69 2 9.85 Total 17,694.73 6279.00 Prefabricated stairs (Colchester) Prefabricated staircases cost £1204 per flight (including allowance for landings). There are 36 stair flights. The total cost to construct prefabricated concrete staircases including landings is therefore £43,344. These staircases are constructed off site and delivered to the site as a modular stairwell. The amount of waste generated on site is negligible. Therefore the construction cost of £43,344 is also equal to the total project cost for this design option. Chelmsford Magistrates’ Court The quantity surveyor was not able to assess the application of the two design solutions to Chelmsford Magistrates’ Court in detail due to insufficient data. As the layout and specifications of the staircases are similar in both buildings, a pro rata approach was adopted to generate the costs and savings generated from Chelmsford (Table A8).


Table A8 Summary of pro rata values for Chelmsford Magistrates’ Court Cast in situ stairs Total cost of construction (£50,983/36 flights = £1,416 48 flights) = £67,977 Total volume of waste (11.27m3/36 flights = 0.313m3 48 flights) = 15m3 Total volume of waste (bulked in skips) (23.37m3/36 flights = 0.649m3 x 48 flights) = 31m3 Total tonnes of waste (12.25 tonnes/36 flights = 0.34 tonnes 48 flights) = 16 tonnes Total cost of waste disposal (£461.89/36 flights = £12.9 48 flights) = £619 Total value of wasted materials (£6279/36 flights = £174 48 flights) = £8372 Prefabricated stairs Total cost of construction (£43,344/36 flights = £1204 48 flights) = £57,792 Summary of cost and environmental benefits (Colchester and Chelmsford) Table A9 summarises the total savings of adopting prefabricated stairs on both the Colchester and Chelmsford projects.

Table A9 Summary of cost and environmental benefits of adopting alternative design at Colchester and Chelmsford

Cost of

construction (£)

Tonnes of waste

Cost of waste

disposal (£)

Value of wasted

materials (£)

Total project cost

(£) Colchester Magistrates’ Court Cast in situ 50,983 12.25 462 6,279 51,445 Prefabricated 43,344 N/A N/A N/A 43,344 Project saving 7639 12.3 462 6279 8101 Chelmsford Magistrates’ Court Cast in situ 67,977 16 461.9 6,279 68,439 Prefabricated 57,792 N/A N/A N/A 57,792 Project saving 10,185 16.0 462 6,279 10,647 Total savings 17,824 28.3 924 12,558 18,748

The waste disposal costs were based on 8yd3 skips (6.1m3). To determine the transport savings associated with the alternative design, the total volume of waste saved (23.4 + 31.2 = 54.6m3) divided by 6.1m3 equals 9 lorry movements would be avoided by implementing the prefabricated solution. Post-tensioned flat concrete slab versus conventional reinforced concrete slab Colchester gross floor area: 2293m2

Chelmsford gross floor area: 2282.6m2

The analysis compared:

Base design: conventional reinforced ribbed slab (600mm depth with 900mm centres); and

Alternative design: post-tensioned flat slab (250–450mm section depth).

Conventional reinforced slab The slab is cast over a polypropylene mould with an internal area of 2516m2 per floor. The life span of this polypropylene would enable the mould to be reused for all floors in the Colchester and Chelmsford buildings.


Table A10 Breakdown of unit rates and wastage rates for conventional reinforced slab

Material Unit rate (including LP&M) Wastage rate (%) Concrete £134/m3 4 Reinforcement £1300/t 10 Plywood for formwork/shuttering £29/m2 100 Polypropylene formwork £45.86/m2 100

Table A11 Base design – cost of construction

Material Total quantity of

material LP&M unit rate

(£/unit) Total LP&M cost (£)

Colchester Magistrates’ Court Concrete (m3) 439 134 58,826 Reinforcement (tonnes) 59 1300 76,700 Formwork/shuttering (m2) 2239 29 64,931 Formwork/polypropylene (m2) 1694 45.86 77,687 Total project 278,144 Chelmsford Magistrates’ Court Concrete (m3) 652 134 87,368 Reinforcement (tonnes) 87 1300 113,100 Formwork/shuttering (m2) 3326 29 96,454 Formwork/polypropylene (m2) 2608 45.86 119,603 Total project 416,525 Total scheme 694,669

Table A12 Base design – volume of waste

Materials Total

quantity of materials

Volume of materials

(m3)

Wastage rate (%)

Waste generated

(m3)

Materials wasted

(tonnes) Colchester Magistrates’ Court Concrete (m3) 439 439 4 17.56 42.14 Reinforcement (tonnes) 59 8 10 0.76 5.90 Formwork/shuttering (m2) 2239 40 100 40.30 28.21 Formwork/polypropylene (m2) 1694 5 100 5.08 6.10 Total project 492 64 82 Chelmsford Magistrates’ Court Concrete (m3) 652 652 4 26.08 62.59 Reinforcement (tonnes) 87 11 10 1.12 8.70 Formwork/shuttering (m2) 3326 60 100 59.87 41.91 Formwork/polypropylene (m2) 2608 8 100 7.82 9.39 Total project 731 95 123 Total scheme 159 205


Waste stream Cost of waste disposal per skip Bulking factor of material Inert £170 0.50 Timber £108 0.50 Plastic £218 0.70 A: The cost of waste disposal for metal is taken to be zero due to its high resale value.


Table A14 Base design – cost of waste disposal

Material Waste

generated (m3)


Cost disposal per skip (£)

Total cost of waste

disposal (£) Colchester Magistrates’ Court Concrete (m3) 17.56 35.12 170 978.75 Reinforcement (tonnes) 0.76 1.51 0 – Formwork/shuttering (m2) 40.30 80.60 108 1427.09 Formwork/polypropylene (m2)

5.08 16.94 218 605.40

Total project 64 134 3011 Chelmsford Magistrates’ Court Concrete (m3) 26.08 52.16 170 1453.64 Reinforcement (tonnes) 1.12 2.23 – Formwork/shuttering (m2) 59.87 119.74 108 2119.92 Formwork/polypropylene (m2)

7.82 26.08 218 932.04

Total project 95 200 4506 Total scheme 159 334 7517

Table A15 Base design – value of wasted materials

Material Total

quantity of material

Material unit rate (£/unit)

Total material cost

(£)

Wastage rate (%)

Value of materials

wasted (exc. P&L) (£)

Colchester Magistrates’ Court Concrete (m3) 439 95 41,705 4 1668.20 Reinforcement (tonnes) 59 800 47,200 10 605.13 Formwork/shuttering (m2) 2239 23 51,497 100 926.95 Formwork/polypropylene (m2) 1694 13.39 22,683 100 68.05 Total project 163,085 3268 Chelmsford Magistrates’ Court Concrete (m3) 652 95 61,940 4 2477.60 Reinforcement (tonnes) 87 800 69,600 10 892.31 Formwork/shuttering (m2) 3326 23 76,498 100 1376.96 Formwork/polypropylene (m2) 2608 13.39 34,921 100 104.76 Total project 242,959 4852 Total scheme 8120 Post-tensioned slab The post-tensioned flat slab solution involves in situ pouring of concrete around sheaths or ducts containing unstressed tendons. Once the concrete gains sufficient strength, the tendons are stressed against the concrete and locked by special anchor grips. This process requires conventional formwork. The post-tension concrete flat slab sections have a depth of 250mm and 450mm at different sections of the buildings. The slab is therefore 150mm thinner than the conventional concrete slab.

Table A16 Breakdown of unit rates and wastage rates for post-tensioned slab

Material Unit rate (including LP&M) Wastage rate (%) Concrete £138/m3 4 Reinforcement £2988/t 10 Plywood for formwork/shuttering £29/m2 100


Table A17 Alternative design – cost of construction

Material Total quantity of material LP&M unit

rate (£/unit) Total LP&M cost

(£) Colchester Magistrates’ Court Concrete (m3) 611 138 84,318 Reinforcement (tonnes) 37 2988 110,556 Formwork/shuttering (m2) 2239 29 64,931 Total project 259,805 Chelmsford Magistrates’ Court Concrete (m3) 908 138 125,304 Reinforcement (tonnes) 55 2988 164,340 Formwork/shuttering (m2) 3326 29 96,454 Total project 386,098 Total scheme 645,903

Table A18 Alternative design – volume of waste

Material Total quantity

of material

Volume of material

(m3)

Wastage rate (%)

Waste generated

(m3)

Materials wasted

(tonnes) Colchester Magistrates’ Court Concrete (m3) 611 611 4 24.44 58.66 Reinforcement (tonnes) 37 5 10 0.47 3.70 Formwork/shuttering (m2) 2239 40 100 40.30 28.21 Total project 656 65 90.57 Chelmsford Magistrates’ Court Concrete (m3) 908 908 4 36.32 87.17 Reinforcement (tonnes) 55 7 10 0.71 5.50 Formwork/shuttering (m2) 3326 60 100 59.87 41.91 Total project 975 97 135 Total scheme 162 225.14


Waste stream Cost of waste disposal per skip Bulking factor of material Inert £170 0.50 Timber £108 0.50 A: The cost of waste disposal for metal is taken to be zero due to its high resale value.

Table A20 Alternative design – cost of waste disposal

Material Waste

generated (m3)


Cost of waste disposal per

skip (£)

Total cost of waste disposal

(£) Colchester Magistrates’ Court Concrete (m3) 24.44 48.88 170 1362.23 Reinforcement (tonnes) 0.47 0.95 0 0 Formwork/shuttering (m2) 40.30 80.60 108 1427.09 Total project 65 130.43 2789.32 Chelmsford Magistrates’ Court Concrete (m3) 36.32 72.64 170 2024.39 Reinforcement (tonnes) 0.71 1.41 0 0 Formwork/shuttering (m2) 59.87 119.74 108 2119.92 Total project 97 4144 Total scheme 162 6933.63


Table A21 Alternative design – value of wasted materials

Material Total

quantity of material


Total material cost (£)

Wastage rate (%)

Value of materials

wasted (exc. P&L) (£)

Colchester Magistrates’ Court Concrete (m3) 611 95 58,045 4 2321.80 Reinforcement (tonnes) 37 800 29,600 10 379.49 Formwork/shuttering (m2) 2239 23 51,497 100 926.95 Total project 139,142 3628.23 Chelmsford Magistrates’ Court Concrete (m3) 908 95 86,260 4 3450.40 Reinforcement (tonnes) 55 800 44,000 10 564.10 Formwork/shuttering (m2) 3326 23 76,498 100 1376.96 Total project 206,758 5391 Total scheme 9020 Cladding The conventional concrete slab (base design) has a depth of 600mm at 900mm centres, but the depths of the post-tensioned flat slab (alternative design) are 250mm and 450mm. The post-tensioned slab is therefore 150mm thinner (at its maximum depth of 450mm). The difference in slab thickness per floor is 150mm, resulting in a total decrease of depth with the post-tensioned flat slab (alternative design) across three floors of 450mm. This will decrease the area of cladding by 86.1m2 in the Chelmsford building (0.45m height increase 191.3m perimeter) and 119.3m2 in the Colchester building (0.45 height increase 265m perimeter) by using the alternative design compared to the base design. This decrease should also result in a corresponding reduction in cost and waste. For the purpose of this exercise, only the reduced area of cladding resulting from using the thinner post-tensioned slab was assessed in terms of cost and waste. It is assumed that 75% of the extra area (the difference between the base and alternative designs) is brick cladding and 25% is copper cladding with plywood backing. Insulation, plasterboard and blockwork will apply to the whole area of extra cladding for each building. Table A22 gives details of the materials used.

Table A22 Total quantity of materials used for extra area of cladding in base design Material Chelmsford Colchester Brickwork (m2) 64.60 89.50 Copper (m2) 21.50 29.80 Plywood (m2) 21.50 29.80 Insulation (m2) 86.10 119.30 Plasterboard (m2) 86.10 119.30 Blockwork (m2) 86.10 119.30 Both buildings have a range of cladding specifications and the Davis Langdon quantity surveyor assessed the cost of cladding to potentially be as high as £550/m2 when elements such as green walls are considered. Table A23 gives a breakdown of material unit rates and wastage rates; 75% brickwork, 25% copper with plywood backing and 100% insulation, plasterboard and blockwork are assumed for the total area of extra cladding required.

Table A23 Breakdown of unit rates and wastage rates for extra area of cladding in base design

Material Unit rate (including LP&M) Wastage rate (%) Brickwork £35/m2 20 Copper £115.72/m2 1 Plywood (backing) £15/m2 1 Insulation £15/m2 15 Plasterboard £5/m2 22.5 Blockwork £18.50/m2 20


Table A24 gives a breakdown of the material quantities and costs (including labour, plant and material) required to construct the extra area of cladding for the Chelmsford building (86.1m2) and Colchester building (119.3m2) in the base design. The total extra cost to the base design is £20,000.

Table A24 Base design – additional cost of construction for extra area of cladding Material Total quantity of materials (m2) LP&M unit rate (£/m2) Total LP&M cost (£) Colchester Magistrates’ Court Brickwork 89.50 35.00 3,132.50 Copper 29.80 115.72 3,448.46 Plywood 29.80 15.00 447.00 Insulation 119.30 15.00 1,789.50 Plasterboard 119.30 5.00 596.50 Blockwork 119.30 18.50 2,207.05 Project total 11,621.01 Chelmsford Magistrates’ Court Brickwork 64.60 35.00 2,261.00 Copper 21.50 115.72 2,487.98 Plywood 21.50 15.00 322.50 Insulation 86.10 15.00 1,291.50 Plasterboard 86.10 5.00 430.50 Blockwork 86.10 18.50 1,592.85 Project total 8,386.33 Total 20,007.34 The total additional waste arising from the extra areas of cladding required when using the conventional floor slab for the whole scheme is 10.88m3 or 14.1 tonnes (Table A25).

Table A25 Base design – additional volume of waste for extra area of cladding

Material Total quantity of

material (m2) Volume of

material (m3) Wastage rate

(%)

Waste generated

(m3)

Materials wasted

(tonnes) Colchester Magistrates’ Court Brickwork 89.50 10.74 20 2.15 3.65 Copper 29.80 0.03 5 0.00 0.01 Plywood 29.80 0.54 5 0.03 0.02 Insulation 119.30 9.54 15 1.43 0.02 Plasterboard 119.30 1.49 22.5 0.34 0.20 Blockwork 119.30 11.93 20 2.39 4.29 Project total 34.27 6.33 8.20 Chelmsford Magistrates’ Court Brickwork 64.60 7.75 20 1.55 2.64 Copper 21.50 0.02 1 0.00 0.00 Plywood 21.50 0.39 1 0.00 0.00 Insulation 86.10 6.89 15 1.03 0.02 Plasterboard 86.10 1.08 22.5 0.24 0.15 Blockwork 86.10 8.61 20 1.72 3.10 Project total 24.73 4.55 5.90 Total 59.00 10.88 14.10


Table A26 Skip costs and uncompacted bulking factors for different wastes associated with extra area of cladding in base design A

Waste stream Cost of waste disposal per skip Bulking factor of material Inert £170 0.50 Timber £108 0.50 Mixed £218 0.50 Plasterboard £101 0.65 A: The cost of waste disposal for metal is taken to be zero due to its high resale value.

Table A27 Base design – additional cost of waste disposal for extra area of cladding

Material Waste

generated (m3) Volume waste with bulking factor (m3)

Cost of disposal per skip (£)

Total cost of waste disposal (£)

Colchester Magistrates’ Court Brickwork 2.15 4.30 170.00 119.72 Copper 0.00 0.00 0.00 0.00 Plywood 0.03 0.05 108.00 0.95 Insulation 1.43 2.86 218.00 102.32 Plasterboard 0.34 0.96 101.00 34.26 Blockwork 2.39 4.77 170.00 170.54 Project total 6.33 12.95 427.80 Chelmsford Magistrates’ Court Brickwork 1.55 3.10 170.00 86.42 Copper 0.00 0.00 0.00 0.00 Plywood 0.00 0.01 108.00 0.14 Insulation 1.03 2.07 218.00 73.85 Plasterboard 0.24 0.69 101.00 24.73 Blockwork 1.72 3.44 170.00 123.08 Project total 4.55 9.31 308.21 Total 10.88 22.26 736.01

Table A28 Base design – additional value of wasted materials for extra area of cladding

Material Total quantity

of material (m2)


Total material cost (£)

Wastage rate (%)

Value of materials wasted (exc. P&L)

(£) Colchester Magistrates’ Court Brickwork 89.50 19.25 1722.88 20 344.58 Copper 29.80 84.48 2517.37 5 125.87 Plywood 29.80 6.00 178.80 5 8.94 Insulation 119.30 11.10 1324.23 15 198.63 Plasterboard 119.30 3.00 357.90 22.5 80.53 Blockwork 119.30 9.25 1103.53 20 220.71 Project total 7204.70 979.25 Chelmsford Magistrates’ Court Brickwork 64.60 19.25 1243.55 20 248.71 Copper 21.50 84.48 1816.23 1 18.16 Plywood 21.50 6.00 129.00 1 1.29 Insulation 86.10 11.10 955.71 15 143.36 Plasterboard 86.10 3.00 258.30 22.5 58.12 Blockwork 86.10 9.25 796.43 20 159.29 Project total 5199.21 628.92 Total 12,403.91 1608.17


Summary of cost and environmental benefits The post-tensioned slab requires larger quantities of concrete and therefore produces more concrete waste than the conventional slab. However, the reinforcement/formwork/extra cladding waste from the conventional slab is greater than the total reinforcement/formwork waste for the post-tensioned slab solution and more than the additional concrete waste from the post-tensioned slab. This explains the waste savings of the post-tensioned slab solution when measured in cubic metres. When measured in tonnes, however, the density of concrete is such that the weight of concrete waste from the post-tensioned slab is greater than the weight of reinforcement/formwork/cladding waste in the conventional slab solution. Tables A29–A31 summarise the impact of adopting the post-tensioned slab design solution compared with the conventional reinforced floor slab for the two separate buildings and project.

Table A29 Summary of cost and environmental benefits of adopting alternative design – Colchester

Design Construction

cost (£) Waste (m3)

Waste (tonnes)

Cost of waste

disposal (£)

Value of wasted

material (£)

Total project cost (£)

Without considering effect of extra cladding with base design Conventional slab 278,144 64.00 82.00 3011 3268 281,155 Post-tensioned slab 259,805 65.00 90.60 2789 3628 262,594 Difference 18,339 (1.0) (8.60) 222 (360) 18,561 Including consideration of effect of extra cladding with base design Conventional slab + extra cladding

289,765 70.00 90.20 3439 4247 293,204

Post-tensioned slab 259,805 65.00 90.60 2789 3628 262,594 Difference 29,960 5.00 (0.40) 650 619 30,610

Table A30 Summary of cost and environmental benefits of adopting alternative design – Chelmsford

Design Construction

cost (£) Waste (m3)

Waste (tones)

Cost of waste

disposal (£)

Value of wasted

material (£)

Total project cost (£)

Without considering effect of extra cladding with base design Conventional slab 416,525 95.00 123 4506 4852 421,031 Post-tensioned slab 386,098 97.00 135 4144 5391 390,242 Difference 30,427 (2.00) (12) 362 (539) 30,789 Including consideration of effect of extra cladding with base design Conventional slab + extra cladding

424,911 99.55 128.90 4814 5481 429,725

Post-tensioned slab 386,098 97.00 135 4144 5391 390,242 Difference 38,813 2.55 (6.10) 670 90 39,483


Table A31 Summary of cost and environmental benefits of adopting alternative design for the project

Design Construction

cost Waste (m3)

Waste (tonnes)

Cost of waste

disposal

Value of wasted material


Colchester Magistrates’ Court Conventional slab £278,144 64 82 £3011 £3268 £281,155 Conventional slab + extra cladding B

£289,765 70 90.20 £3439 £4247 £293,204

Post-tensioned slab £259,805 65 90.60 £2789 £3628 £262,594 Project savings £29,960 5 (0.40) £650 £619 £30,610 Chelmsford Magistrates’ Court Conventional slab £416,525 95 123 £4506 £4852 £421,031 Conventional slab + extra cladding B

£424,911 99.55 128.90 £4814 £5481 £429,725

Post-tensioned slab £386,098 97 135 £4144 £5391 £390,242 Project savings £38,813 2.55 (6.10) £670 £90 £39,483 Total savings £68,773 7.55 (6.50) £1320 £709 £70,093 Further calculations may show that the savings in the height of the building from using the thinner post-tensioned slab would also reduce the concrete in the columns and staircases for both buildings. This would reduce concrete waste and potentially lead to further waste savings from using the post-tensioned slab. CFA replacement piles Base design: one CFA replacement pile, 900mm diameter, per location of column; and

Alternative design: two CFA replacement piles, 600mm diameter, per location of column.

The calculations below are based on a total of 65 column bases at ground level on the Colchester site. The results are then used on a pro rata basis to determine the results for 57 column bases at the Chelmsford site. Base design – Colchester Magistrates’ Court Each CFA pile extends to a depth of 20m, giving a total depth of 1300m for the 65 column bases. The wastage rate, which was determined by calculating the area of piling, was provided by the quantity surveyor and accounts for the total amount of excavation waste arising. The total weight of waste was 1612 tonnes (based on density of fill = 2.0 tonnes/m3).

Table A32 Basic design – cost of construction

Material Number of

piles Depth of CFA

pile (m) Unit rate of pile (£/m) A

Cost of construction (£)

One 900mm diameter CFA pile 65 20 105 136,500 Total 136,500 A: Including labour, plant and material.

Table A33 Basic design – volume of waste

Material Number of

piles Area of pile

(m2) Length of pile

(m) Waste generated

(m3) One 900mm diameter CFA pile 65 0.64 19.5 806 Total 806


Table A34 Basic design – cost of waste disposal

Material Waste generated

(m3) Cost of disposal

(£/m3) Cost of waste disposal (£)

One 900mm diameter CFA pile 806 20 16,120

Total 16,120 Alternative design – Colchester Magistrates’ Court The alternative design involves the application of two adjacent CFA replacement piles of 600mm diameter per location of column. Each pair of CFA piles extends to a total depth of 34m (two piles at 17m each), giving an overall total depth of 2210m at the Colchester site. The wastage rate was provided by the quantity surveyor and accounts for the total amount of excavation waste arising determined by calculating the area of piling. The total weight of waste is 1250 tonnes (based on density of fill = 2.0 tonnes/m3).

Table A35 Alternative design – cost of construction

Material Number of

piles Depth of CFA

pile (m) Unit rate of pile (£/m) A

Cost of construction (£)

Two 600mm diameter CFA piles 65 34 55 121,550 Total 121,550 A: Including labour, plant and material.

Table A36 Alternative design – volume of waste

Material Number of piles Area of pile (m2)Length of pile

(m)

Waste generated

(m3) Two 600mm diameter CFA piles 65 pairs 0.57 per pair 17 625 Total 625

Table A37 Alternative design – cost of waste disposal

Material Waste generated

(m3) Cost of disposal

(£/m3) Cost of waste disposal (£)

Two 600mm diameter CFA piles 625 20 12,500

Total 12,500 Chelmsford Magistrates’ Court The Chelmsford Magistrates’ Court project was not assessed in detail due to insufficient data. As the layout of the foundation piles is similar on both buildings, a pro rata approach was adopted to generate the costs and waste savings for Chelmsford (Table A38).

Table A38 Pro rata costs for Chelmsford Magistrates’ Court Base design – one 900mm diameter CFA pile Total cost of constructing 900mm diameter piles £136,500/65 piles = £2,100 57 piles = £119,700 Total tonnes of waste 1612 tonnes/65 piles = 24 tonnes 57 piles = 1413.6 tonnes Total cost of waste disposal £16,120/65 piles = £248 57 piles = £14,136 Alternative design – two 600mm diameter CFA piles Total cost of constructing 900mm diameter piles £121,550/65 piles = £1,870 57 piles = £106,590 Total tonnes of waste 1250 tonnes/65 piles = 19 tonnes 57 piles = 1096 tonnes Total cost of waste disposal £12,500/65 piles = £192 57 piles = £10,962


Transport savings – both sites

Table A39 Transport savings through adopting alternative design Volume of waste (m3) Number of lorry movements Colchester Magistrates’ Court 900mm diameter CFA pile 806 54 2 x 600mm diameter CFA piles 625 42 Project saving 12 Chelmsford Magistrates’ Court 900mm diameter CFA pile 706 47 2 x 600mm diameter CFA piles 548 37 Project savings 11 Scheme savings 23 A: Assuming 15m3 is transported per lorry.

Table A40 Summary of cost and environmental benefits of adopting alternative design for the project

Design Construction

cost Waste (m3)

Waste (tonnes)

Cost of waste

disposal


Colchester Magistrates’ Court 900mm diameter CFA pile £136,500 806 1612 £16,120 £152,620 2 x 600mm diameter CFA piles £121,550 625 1250 £12,500 £134,050 Project savings £14,950 181 362 £3620 £18,570 Chelmsford Magistrates’ Court 900mm diameter CFA pile £119,700 707 1414 £14,136 £133,836 2 x 600mm diameter CFA piles £106,590 548 1096 £10,962 £117,552 Project savings £13,110 159 318 £3174 £16,284 Total savings £28,060 340 680 £6794 £34,854 Retain excavation material as piling mat versus dispose and import aggregate The following two methods of construction were compared:

Base design: disposal of all excavated material and import of aggregate for piling mat; and

Alternative design: retention and recycling of a proportion of the excavated material for use as a piling mat

and disposal of the remaining material.

The total volume of excavated material available at the Colchester site is 1655m3 based on levelling the site to a depth of 400mm below existing ground levels. Focusing solely on the Colchester site, there is a requirement of 954m3 of material to be used in the piling mat. Disposal of excavated material and import of aggregate The quantitative analysis considered:

the excavation and disposal of 1655m3 of material on the Colchester site based on levelling the site to a depth

of 400mm below existing ground level; and

importing 954m3 of suitable aggregate for the piling mat.



Table A41 Basic design – total project costs (Colchester only)

Material

Total volume

of material

(m3)

Unit rate of excavation

and disposal (£/m3)

Cost of excavation

and disposal

(£)

Unit rate importing material (£/m3)

Cost of importing material

Project cost

Excavation and disposal 1655 23 38,065 38,065 Import piling mat material 954 35 33,390 33,390 Total project cost 71,455 The wastage rate for excavated material is 100%, therefore the total volume of material wasted is 1655m3. Assuming a fill density of 2.0 tonnes/m3, this is equal to 3310 tonnes of waste. At a unit rate of £20/m3, its disposal would cost £33,100. Retain excavated car-park as piling mat There is potential to retain and crush 954m3 of the excavated material available on site for storage and recycling for use as the piling mat. The remaining 701m3 of excavated material would be disposed off site, equivalent to 1402 tonnes of waste (assuming a fill density of 2.0 tonnes/m3). The wastage rate is therefore approximately 42%. At a unit rate of £20/m3, disposal of the unwanted material would cost £14,020.

Table A42 Alternative design – cost of construction (Colchester only)

Material

Volume of material retained

(m3)

Volume of material disposed

(m3)

Unit rate of

excavation and

crushing (£/m3)

Unit rate for moving excavated

material on site (£/m3)

Unit rate for excavation

and disposal of remaining

material

Project cost

Excavate, crush and move retained material 954 10 3 12,402

Excavation and disposal 701 23 16,123 Total project cost 28,525

Table A43 Transport savings through adopting alternative design A (Colchester only)

Volume of imported

material (m3) Volume of waste

(m3) Number of lorry

movements Base design 954 1655 174 Alternative design 0 701 47 Project saving 954 954 127 A: Assuming 15m3 is transported per lorry.

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