STEEL CONSTRUCTION Cost. Updated February 2016

Transcription

1 STEEL CONSTRUCTION Cost Updated February 2016

2 2 COST Steel for Life and the British Constructional Steelwork Association (BCSA) are working closely together to promote the effective use of structural steelwork. This collaborative effort ensures that advances in the knowledge of the constructional use of steel are shared with construction professionals. Follow us on: LinkedIn: steelconstruction.info Steel is, by some margin, the most popular framing material for multi-storey buildings in the UK and has a long track record of delivering high quality and cost-effective structures with proven sustainability benefits. Steel can be naturally recycled and re-used continuously, and offers a wide range of additional advantages such as health and safety benefits, speed of construction, quality, efficiency, innovation, offsite manufacture and service and support. Facebook: steelconstruction.info Google+: steelconstruction.info The steel sector is renowned for keeping specifiers abreast of the latest advances in areas such as fire protection of structural steelwork and achieving buildings with the highest sustainability ratings. Recent publications have provided detailed guidance on Fire Protection and CE Marking and what it means for the construction sector. Guidance is provided on all relevant technical developments as quickly as is possible. The sector s go to resource website is a free online encyclopedia for UK construction that shares a wealth of up-to-date, reliable information with the construction industry in one easily accessible place. This publication has been funded by Steel for Life and would not be possible without the support of our sponsors. Headline sponsors: BARRETT STEEL LIMITED Gold sponsors: AJN Steelstock Ltd Ficep UK Ltd National Tube Stockholders and Cleveland Steel & Tubes Parkersteel Wedge Group Galvanizing Ltd Silver sponsors: Hadley Group, Building Products Division Jack Tighe Ltd Bronze sponsors: BAPP Group of Companies Barnshaw Section Benders Limited Hempel Joseph Ash Galvanizing Kaltenbach Limited Tension Control Bolts Ltd

3 COST 3 Contents Cost Planning 4 Cost Planning Structural Steelwork How to Get it Right 4 Steel Insight Series Getting Started Creating Initial Estimates 7 Why creating robust initial estimates is important Initial estimates overview Initial estimates a useful methodology What factors can affect initial estimates? Building function and facilities Location and site constraints Market conditions Analysing Options During Concept Design 12 Analysing Options During Design Development 13 Methodology during design development Types of steel frame The design of the frame Quantifying the frame s weight Section sizes and availability Connections and fittings Erection costs of the frame Fire protection Other elements Methodology for Costing Specialist Systems 19 Examples of specialist systems Summary 20 Cost Tables 21 Cost Comparison 23 Introduction 24 Building 1 A Typical Business Park Office Building 25 Programme Comparison 26 Logistics and Buildability 28 Cost Comparison 29 Key Costs per m 2 GIFA 29 Summary 30 Building 2 A Typical City Centre Office Building 31 Programme Comparison 33 Logistics and Buildability 35 Cost Comparison 36 Key Costs per m 2 GIFA 36 Embodied Carbon Comparison 37 Summary 39

4 4 COST Cost Planning Cost Planning Structural Steelwork How to Get it Right The configuration and material of a building s frame are usually chosen early in the design process changing them later can have significant programme and cost implications and a consequential impact on the design of other major building elements. It is therefore crucial to support informed decision-making with realistic cost information at the early stages of the project. Steel frames consistently capture a market share in the multi-storey non-residential building market of around 70% and cost advantages are often cited as a key reason in selection of the framing material. It is therefore very important to understand how to cost it accurately. Market Share for Structural Frames in Multi-Storey Buildings 80% 70% % Based on Floor Area 60% 50% 40% 30% 20% 10% 0% Steel Insitu Concrete Precast Concrete Load Bearing Masonry Timber

5 COST 5 This guide is designed to take building professionals through each stage of the cost planning process and it sets out the primary considerations when cost planning during the initial design stages, through option analysis and into detailed design to support informed decision-making throughout the design process. Setting elemental target costs Option analysis Design progression Costing during detailed design It is based on the Steel Insight articles prepared by Gardiner & Theobald, which are published quarterly. Cost information in this publication is current at Q The cost data is updated each quarter and the latest figures are available on Articles of interest: COST OF STRUCTURAL STEELWORK COST COMPARISON STUDY See also Electronic version of Steel Construction: Cost CONSTRUCTION NEWS

6 6 COST All of the Steel Insight series can be viewed or downloaded from: CONSTRUCTION NEWS Steel Insight Series Published on a quarterly basis, Gardiner & Theobald have written 15 articles in this series thus far. This guide covers content included in articles 1, 2, 3 and 9 with the latest cost data from article 15. Following the methodology set out in this guide, more detailed guidance on the key factors for specific sectors can be found in articles 4-8, covering multi-storey buildings and buildings for the education, industrial, healthcare and commercial sectors, respectively. This more detailed guidance was revisited in article 10. The impact of topics primarily associated with each sector has also been included. Article List 1. Pricing of structural steelwork 2. Cost planning through design stages 3. Comparative cost study Multi-storey offices 4. Cost planning of steel framed multi-storey buildings 5. Education buildings 6. Industrial buildings 7. Healthcare buildings 8. Multi-storey commercial buildings 9. Cost planning structural steelwork 10. Key frame cost drivers 11. Cost update and case studies: commercial buildings 12. Cost update and case studies: industrial buildings 13. Cost update and case studies: retail buildings 14. Cost update and case studies: leisure buildings 15. Cost update and case studies: education buildings Topics Thermal mass (article 5) Embodied carbon (article 6) Vibration (article 7) Fire protection and service integration (article 8) The data and rates contained in this guide and the articles listed above have been produced for comparative purposes only and should not be used or relied upon for any other purpose without further discussion with Gardiner & Theobald LLP. Gardiner & Theobald LLP does not owe a duty of care to the reader or accept responsibility for any reliance on the foregoing.

7 COST 7 Getting Started Creating Initial Estimates Why creating robust initial estimates is important In most projects, the decision on the structural frame material is made early in the design process. From that point the frame is unlikely to change, as to do so could have significant programme implications and impact on the design of other major elements such as foundations, finishes and cladding. It is important to get the frame selection decision right, even though it is made very early in the design process While cost is not the only reason project teams choose a particular frame type, it is a key consideration, and realistic cost information is important at this early stage to support their decision-making. Getting it wrong can mean the incorrect frame solution may be chosen, which can result in higher costs for both the frame and other related building elements. It can also have an effect on buildability, logistics and the whole construction programme and, as the frame construction is usually a critical path activity, any increase to the construction programme will have an associated impact on project cost.

8 8 COST Initial estimates overview Initial cost estimates are usually based on outline architectural design proposals, and the cost consultant may therefore Setting elemental target costs only have a limited amount of information to work with. Option analysis Design progression Costing during detailed design Ensure that costing methodology considers the impact of frame selection on other elements such as foundations, cladding and services installations As information is limited, measurement will generally only consider overall floor areas and cost consultants typically use cost models, benchmarks and other historic data to inform a rate per m 2 gross internal floor area (GIFA) for the frame and other building elements. At this point, it is important to understand how to adapt benchmark or standard ranges to suit the project rather than arbitrarily using the highest or lowest rate of a range. As more information becomes available, different structural options can be analysed and compared, including specialist systems to aid the developing design. Rather than simply comparing the cost of the different frame components, these cost analyses also need to consider the impact the frame might have on other elements, such as substructure, cladding and M&E services installations to enable a holistic comparison. As the design develops further and more information becomes available, more detailed cost planning can be undertaken as the cost consultant can quantify key components and test the initial allowances against the actual building. At this later stage, the cost estimating methodology for a structural steel frame shifts from using a cost per m 2 of floor area, based on adjusted benchmark rates, to quantifying the steel elements and pricing per tonne. But when preparing cost estimates, it is also important to include allowances for other factors that may not yet be quantifiable, including allowances for connections and fittings, the required fire resistance period and fire protection materials needed, and how the frame will be constructed on-site.

9 COST 9 Initial estimates a useful methodology The tools for a cost consultant during the early design stages of any project are cost models, benchmarks and historic cost data. At this stage, estimated costs will be expressed elementally as a rate per m 2 GIFA. Typical cost ranges for different frame types can be developed through cost models, but a number of key factors will change from project to project and their impact on the cost of the frame will therefore vary between projects. Avoid simply taking the highest value of the benchmarked standard range It is important to not just use the highest rate of a standard range, instead a good understanding of the project and how the standard ranges should be adapted to suit the project specific factors is required. To do this most effectively, the cost consultant needs to ask relevant questions of the design team to gain an understanding of the project s cost drivers for the frame and to approach steelwork contractors for current and future market prices, as this provides a more accurate estimating base than relying on indices to adjust benchmark or historic rates. Understand how standard ranges should be adapted for the project being considered

10 10 COST What factors can affect initial estimates? They can include: Building function and facilities Location and site constraints Market conditions Procurement route Setting elemental target costs Option analysis Design progression Costing during detailed design Building function and facilities The proposed usage of a building influences the design of the frame in many ways, including the design loadings, grid, floor-to-floor heights and whether clear spans are required. BUILDING FUNCTION FACTORS Steel intensity (kg/m 2 ) Floor-to-floor heights Mix of different spaces Any specialist requirements? This means the overall weight of frame material varies from building to building. For instance, a simple low eaves industrial portal framed building might have a steel frame weight (or intensity) of 40kg/m 2 GIFA, while the frame for a multi-storey office with long spans to minimise internal columns may weigh more than twice that. Using the same cost range for both buildings would be misleading and either significantly underestimate or overestimate the cost, depending on the steel intensity chosen. A cost consultant therefore needs an understanding of what the building will be used for, and what the floor-to-floor height will be a GIFA rate is based on the floor area, and will not account for significant variances in floor-to-floor heights from those used in standard cost models. This enables the most appropriate standard cost range to be selected as the base for the initial frame elemental target cost. While standard cost ranges based on previous project data are useful tools, it is still crucial to find out as much about the facilities and function of the building as possible. For instance, an open plan office will require fewer columns, requiring longer spanning beams and heavier steel sections, which can increase the overall weight of the frame, (and its cost) while an out-of-town business park type office may have a shorter and more regular grid and a lower overall cost. Projects with a range of different spaces such as atriums and boardrooms will have different grid and loading requirements to a building with a repetitive, regular grid and loadings, which will also impact on overall frame weight and cost. The consultant may also need to consider whether there are any specialist spaces with special acoustic or vibration control requirements, such as those needed in hospital operating theatres, as this also impacts on the frame design and is unlikely to be contained within standard cost ranges. Consulting with the architect and structural engineer can help confirm the design assumptions and principles used when determining the rate to be included in early estimates for the structural frame.

11 COST 11 Location and site constraints The location of the project and site conditions have a major impact on the potential costs. The most commonly used guide to cost indices for different locations is the Building Cost Information Service (BCIS) from the Royal Institute of Chartered Surveyors. It is important to adjust the rate for the proposed location to make sure that the different local market conditions are taken into account using a City of London benchmarked rate (BCIS index 131) for a new project in Cardiff (BCIS index 92) would significantly affect the accuracy of the estimate. SITE LOCATION Use BCIS indices to adjust rates The site itself also has a direct impact on the proposed building s design and cost in many ways. For instance, it may affect the floor plate configuration, building height and the regularity of the structural grid. A regular, repeating grid is the most cost efficient option, and if non-standard sections or a wide range of different sections and connections are needed, the project will be more complex and therefore more expensive as fabrication costs will be higher. Some buildings have specialised requirements, such as retaining a historic façade, close neighbours or poor ground conditions to overcome and if these require complex structural solutions such as transfer structures and heavy fabricated beams, the bespoke fabrication costs will push up the overall cost and may also add to installation time and cost. Building height and site footprint will also cause variations in costs. For example, a multi-storey building with small floor plates will have a heavier steel frame per m 2 GIFA than a low rise building with larger floor plates of the same overall area. The cost consultant should also take note of logistics and access as this affects the cost of erecting the steel frame. Even where two buildings have a similar frame design, costs will differ if one is in a congested city centre while the other is in an easy-access business park as the logistics and access arrangements will vary significantly. Working in built-up areas may also mean restrictions to working hours, noise, deliveries, access and use of cranes. These all influence installation costs and can increase the construction programme with associated expense to the project. SITE SPECIFIC FACTORS Floor plate configuration Regularity of structural grid Building height Transfer structure? Logistics Restrictions to working? Market conditions Cost consultants should also consult with the supply chain to make sure their estimate reflects the supply chain s detailed knowledge of order books and material prices, now and in the immediate future.

12 12 COST Analysing Options During Concept Design The impact of speed of construction on programme and preliminaries costs should be included in the assessment of different options After the initial construction budget has been developed and the design progresses into the concept design stages, Setting elemental target costs Option analysis Design progression Costing during detailed design it is good practice to review a number of alternative structural solutions for both frame and floors. The different options can include reinforced insitu concrete, post-tensioned concrete, precast concrete, timber and structural steelwork and a number of sub options for each type of material including different floor types. Often the number of options to consider can be between five and 10, although it is good practice to reject options if initial considerations prove that they are unworkable or will be uneconomical, for example larger spans using reinforced insitu concrete that will result in prohibitively large members. The key at this stage is to set out the cost of the alternative frame and floor solutions proposed based on a holistic review of not only the structural elements but the impact of each option on other building elements and programme too. The different frame options can impact on the cost of the foundations due to differing frame weights and configurations, on cladding costs due to the differing requirements for horizontal structural zones and therefore overall building height and on services installations due to differing services zones, routes and strategies. Different frame options also impact on the cost of: Foundations Cladding costs Services installations Preliminaries Once comparative costings for the alternative options are completed, it is common to convert the costs back to a cost per m 2 GIFA so that they can be more readily compared with the original elemental budget allowance, and between the alternative solutions. As the options analysis is concluded the impact on programme should also be considered, which could affect preliminaries costs, the impact on a requirement to hand over the building by a certain date and whether the favoured option is consistent with the design intent for the building.

13 COST 13 Analysing Options During Design Development Initial elemental cost estimates enable a target budget for the frame to be developed and option analyses during concept design enable the project team to decide on the key elements of the building design, including frame material and configuration. Once those have been agreed, the details of the design can be developed and putting a realistic costing on all options for major elements in the building is important so correct choices can be made. For the steel frame, this can include the consideration of specialist systems to optimise floor-to-ceiling heights or integrate services and comparisons of possible fire protection methods for the structure. Setting elemental target costs As the design progresses, detailed information on the proposed frame becomes available from the structural engineer drawings showing the frame configuration, cores and shear walls, columns and beams, section sizes and types, floor construction types and the strategy for integrating mechanical and electrical services. As it becomes possible to quantify these elements within the building and allocate rates to the measured items, the methodology of costing the structural steel frame changes. Instead of being costed by using a rate per m 2 GIFA, the individual steel framing elements are measured and a rate per tonne applied. Methodology during design development Option analysis Design progression Costing during detailed design Once the project progresses into the detailed design stage, cost estimates of structural steelwork break the design down into individual components columns, beams, special sections etc. Connections and fire protection are usually then considered separately. CHECKLIST DURING DETAILED DESIGN 1 Types of steel frame 2 The design of the frame 3 Quantifying the weight of the frame 4 Section sizes and availability 5 Connections and fittings 6 Erection costs of the frame 7 Fire protection 8 Other elements Cost consultants need to make sure they understand each of the design drivers for each element of the structural frame in order to arrive at the most appropriate rate per tonne to apply to each of the structural elements. The checklist needs to include: Types of steel frame Quantifying the weight of the frame Connections and fittings Fire protection The design of the frame Section sizes and availability Erection costs of the frame Other elements

14 14 COST Types of steel frame Articles of interest: STEEL SECTION SIZES FLOOR SYSTEMS Each building and site has individual requirements, and there are many choices for the structural products used to form the steel frame. Setting elemental target costs Option analysis Design progression Costing during detailed design When producing cost estimates while the design is developing, information should be sought on the proposed structural products and systems along with any related considerations that could influence the choice, such as the strategy for integrating services. The most widely used structural steel products are rolled I-sections, known as universal beams (UBs), and universal columns (UCs). Other commonly used products are structural hollow sections, which can be square (SHS), circular (CHS) or rectangular (RHS). More information on standard forms of construction can be found in the articles for the following sectors: Multi-storey office buildings Industrial buildings Retail buildings Healthcare buildings Education buildings Leisure buildings Residential and mixed use Fabricated plate girders are used to support heavy loads or span long distances beyond the capability of the largest standard rolled I-sections, for example in bridges. They are usually I-sections made up of plates welded together to form the flanges and web. For very long spans, built-up trusses comprising horizontal, vertical and diagonal members are often used to achieve the most economical solution, e.g. in the roof structures of very large industrial buildings. Cost consultants should receive information on which member types are proposed in the design. Because different products have different fabrication and erection requirements, the rates per tonne differ. The specific building configuration proposed can also affect the volume of steel used. For instance shallower floors can be created using UCs or proprietary shallow floor systems. This could double the weight of steel needed compared with a more traditional approach with deeper floors using UBs, but will decrease the height of the building, which may lead to significant cost savings for the cladding. Fire protection costs will also be reduced due to the inherently greater fire resistance of heavier steel sections. The design of the frame In designing a frame, primary column locations are usually determined by the architectural layouts, which then determines where the other primary members go. The size and weight of the steel members is determined by: Dead load the building s own weight Live load loads imposed on the building during its use, which vary for different functions Wind load this loading will vary depending on the location of the building

15 COST 15 Quantifying the frame s weight When the primary and secondary members have been sized and selected, the cost consultant will measure the length of each structural member and multiply it by the relevant weight (in kg/m) to give the total weight of the frame elements. The weight per metre should be provided by the structural engineer, however for certain sections it may not be apparent so reference to standard steel section property tables will be necessary e.g. angles, channels and hollow sections. Article of interest for section property tables: THE BLUE BOOK Proportional factors of total frame cost Steelwork Design 2% Raw Material 30-40% Fire protection 10-15% Erection 10-15% Fabrication 30-40% Transport 1% The cost of each element of the structural frame is then calculated by applying a rate per tonne to each of the different components, then totalling them. This rate includes all elements of the cost of the section the raw material, detailing, fabrication, transportation and erection. It is often assumed that a frame with the minimum tonnage will be the cheapest. As the chart shows, while raw materials typically account for 30-40% of the total frame cost, fabrication costs also account for the same proportion. Minimum weight does not necessarily mean minimum cost As well as considering the overall weight of the frame, it is also therefore important to understand the components of that frame. The rate per tonne for more complex frame designs is likely to be higher than for a standard frame, because non-standard sections, complex connections or specialist systems have higher fabrication and steelwork contractor design requirements. Indeed, steelwork contractors costs are driven just as much by the man hours required to fabricate the frame as by the amount of material they use. The most cost-effective solutions balance material cost with fabrication/ erection time Section sizes and availability Availability can also make a big difference to the potential cost of proposed products for a structural frame. A product that looks lighter or more cost-effective on paper may in fact be more expensive than a heavier alternative section if it has limited availability and it may delay the programme if sufficient quantities cannot be sourced in time. Popular sections may be manufactured three or four times more often than less common sections, and sometimes it is more cost-effective to use heavier options if they are more readily available. A cost consultant should talk to a steelwork contractor early in the process to identify any products or systems where availability may be an issue, so this can be fed back to the design team or incorporated in the cost estimates through adjusted allowances.

16 16 COST Connections and fittings When the primary and secondary members have been designed, quantified and costed, the consultant needs to consider allowances for those items that Setting elemental target costs cannot yet be quantified, including connections and fittings. Option analysis Design progression Costing during detailed design Standard allowance for connections and fittings is to add 5-10% to the frame weight A separate allowance usually a percentage is generally included for additional plates and fabrication at column bases, beam-to-beam and beam-to-column connections, bracing connections, column splices and haunches etc. In a typical multi-storey building, fittings and connections can make up 5-10% of the weight of the frame, but can account for a higher proportion of the total frame cost because the cost of connections is largely related to their complexity as well as their weight. The most cost-effective approach has a high level of standardisation and repetition to take advantage of reduced material costs, quicker and cheaper fabrication and ready availability. For complex structures standard connections cannot always be used and in these cases cost allowances will need to be higher. Site conditions can also increase the proportion of the connection cost of the total frame for example, if spliced beams are required to enable steel structures to be erected in existing buildings. The key is to achieve the best balance between material cost and the cost of fabricating the connections. Initial designs may try to reduce costs by using the lightest columns, but this may mean extra welded stiffeners are needed, adding cost and weight to the design. Small increases in the beam or column weights may mean the stiffeners can be omitted, reducing fabrication costs and therefore the total cost of the frame. Erection costs of the frame Long span layouts are faster to erect than short span alternatives as they have fewer pieces Erection of the steel frame typically accounts for around 10-15% of the total frame cost, so the cost consultant should always consider whether the building or site will have features that could affect the erection cost. The amount of repetition, piece count, type of connections and site access can all have a significant impact on the cost of constructing the frame and the construction programme. For example, a long span layout may weigh more, but it will be erected faster than a short span frame because it has fewer beams and columns. Similarly, repetitive structures not only bring cost savings during fabrication a repetitive grid with standard components also reduces construction time.

17 COST 17 Fire protection Fire protection typically accounts for around 10-15% of the steel frame cost in commercial multi-storey buildings, so the fire resistance of the structure and the choice of fire protection materials are a key consideration. The procedure for determining fire protection is covered in the recent publication Steel Construction: Fire Protection that can be downloaded from As with all construction materials, when temperatures increase in a fire, steel begins to lose its strength. Fire protection ensures that the structure meets the required fire resistance period to allow occupants to safely evacuate the building. Fire resistance periods for buildings are expressed in terms of the length of time the structure must remain structurally sound in a fire and they depend on the type of building, its occupancy and the size of the steel members. It can be more economical to use slightly heavier structural members, which require less fire protection than lighter sections because of the increased thickness of the steel. This may allow the fire resistance period to be achieved with less fire protection material and a reduced overall cost. For large or complex projects, a specialist fire engineered approach may give the most economic solution. This considers where the actual risks in fire are, rather than relying on the simpler prescriptive one size fits all guidance from the Approved Documents. This approach can lead to reduced fire ratings for some elements of the structure and lower costs of fire protection, without compromising safety. When the fire resistance period for the project has been established, the selection of the appropriate fire protection materials is also important different methods have significant cost differences. It may be useful to seek advice from the supply chain before the design is finalised. Fire protection is a significant cost and giving timely consideration can improve the cost efficiency A mix of different fire protection methods may often be used on a project, so allowances for fire protection should be discussed with both the structural engineer and architect as the method adopted will depend on both performance and aesthetic requirements. There are a number of fire protection materials available, including: Intumescent coatings now the predominant method for fire protection in the UK, these are thin film coatings that swell when heated to insulate the steel. Less than 1mm thick provides 60 minutes fire resistance, and up to 90 minutes resistance can be achieved at a competitive cost. Up to 120 minutes is available at a premium. Boards often used where the structure will be visible, such as to exposed columns. They provide a clean, boxed appearance and can be pre-finished or suitable for decoration. They can be relatively expensive and slower to apply than alternatives.

18 18 COST Cementitious sprays these have now almost disappeared from the UK fire protection market. The finish is not considered visually appealing and, as Setting elemental target costs Option analysis Design progression Costing during detailed design spraying is a wet trade, it can require surrounding areas to be sealed off, increasing the time on-site. Concrete Concrete encasement was the most common form of fire protection for structural steelwork until the late 1970s, but the time, cost and impact on the usable space of the building means it is seldom used today. It may still be used where resistance to impact is important, such as in some car parks and industrial buildings. Using concrete to fill structural hollow sections is sometimes used to provide the necessary fire resistance and increase the sections load carrying capacity. Market share of Fire Protection Systems (Beams & Columns) 60% 50% Market share based on floor area 40% 30% 20% 10% 0% Other sprays Off-site intumescent On-site intumescent Board Encasement Others Other elements Cost consultants also need to include separate cost allowances for preparation and coating works (primers, corrosion protection etc.) as well as connections to other structures.

19 COST 19 Methodology for Costing Specialist Systems Sometimes, a number of structural solutions can be adopted, or the structural frame may need to address a specific design requirement such as minimised structural floor zones or integration of services. In these cases, it is common to evaluate the cost benefits of using a more specialist system such as shallow floor construction or cellular beams. It is important not to look at the cost specialist systems such as cellular beams, shallow floors or steel bearing piles, in isolation When preparing these costings, it is crucial to consider the impact the use of the specialist system could have on the cost of the other building elements and not to limit the comparison to the structural frame costs in isolation. Some elements of specialist systems may mean they add cost to the structural frame, particularly as they are often more complex and procured from more limited sources. However, because they can create benefits such as a quicker programme, or enable shallower floors which reduce cladding costs, the overall cost for the building can be lower than using an alternative measure to achieve the same design objective. The supply chain can provide valuable information on the availability and cost of products and specialist systems, feedback on the complexity of the proposed structure and its connections and current lead times. Examples of specialist systems Where long spans are needed, floor beams often need to be deep to provide the necessary stiffness. This requires heavier steel sections and can significantly increase the structural floor zone. One solution typically adopted for multi-storey commercial buildings is to use lighter sections fabricated from steel plates or rolled sections to form cellular beams with pre-formed openings. Consider the impact of the system on elements such as fire protection, foundations, cladding, services integration and the construction programme to get a representative total cost The depth of these sections is flexible to suit design requirements, and the majority of services can be easily routed through the openings so they are contained within the structural zone, therefore reducing the floor-to-floor height compared to using UBs. A cellular beam costs more per tonne than a standard rolled section, but it can reduce total frame weight by 30% over longer spans. This has an impact on substructure, and by creating a shallower floor and services zone the overall height of the building can be reduced to save cladding costs. A range of proprietary shallow floor systems can also allow floor-to-ceiling heights to be maximised without affecting the height of the building.

20 20 COST Summary Choosing the frame material and configuration of a project is a key early design decision, usually based on initial outline Setting elemental target costs information and comparative budget costings. Option analysis Design progression Costing during detailed design Realistic cost information is vital in supporting decision-making even in the earliest stages changing the frame type later can have a severe impact on the programme implications and design of other major building elements. Cost models and benchmarks are key tools at these early stages. Cost consultants need to develop a thorough understanding of both the project and the historic cost data used so they can adapt standard cost ranges to suit the project s specific factors. This should involve considering a number of key cost drivers including building function, sector, location and site constraints, as well as current market conditions and the proposed procurement route. When undertaking cost analyses of alternative structural options or systems, it is important not just to review frame costs in isolation. The impact that frame choice has on related building elements, such as substructure, cladding and M&E installations, must also be accounted for in comparative costings. Consultation with the supply chain is important to ensure costings are realistic Once the frame type has been selected and the design developed, the initial budget will be tested against the emerging design of the actual building through a quantification of the key components. At this stage, the key cost drivers considered during early estimates, such as function and site constraints, will be reflected in the designs used for cost planning. It is also important to consider factors such as section sizes and availability, connections, fire protection requirements and construction methodology to ensure that an appropriate rate per tonne is selected. Consideration of these key factors throughout the design stages along with early consultation with the supply chain can help make sure that realistic costing of the steel frame and associated elements is maintained and improved as the design develops.

21 STEEL CONSTRUCTION COST 21 Cost Tables

22 22 COST This page will be updated regularly by Gardiner & Theobald in the electronic version of this guide Table 1 below summarises the structural frame costs of three building types and also provides some indicative cost information on floor types and fire protection. The data has been prepared by Gardiner & Theobald and reflects the latest tender price increases seen in Q It should be noted that typical costs are based upon the particular project being attractive to the market and the selection of an appropriate procurement route. Tender price increases from Q3 to Q mean that consideration should be given to the inclusion of inflation allowances for estimates that are expected to be tendered in the remainder of The indicative range given for fire resistance is suitable for buildings with a requirement for 60 minute fire resistance. Buildings with a requirement for 90 minute fire resistance or higher will be outside of this range. To use the table: a) identify which frame type most closely relates to the proposed project, b) select and add the preferred floor type, and c) add fire protection if required. For example, for a low rise, short span framed building in the City of London with a composite metal deck floor and 60 minutes fire resistance, the overall frame rate (based on the average of each range) would be: = per m² GIFA. For other locations, the rates should be adjusted using location indices; Table 2 contains a selection of indices as published and updated by the Building Cost Information Service (BCIS). Before using such standard ranges it is important to confirm the anticipated frame weight and variables such as the floor-to-floor heights to determine whether they are above or below the average and to adjust the rate used accordingly. Similarly, all of the other key cost drivers of complexity, site conditions, location, function, logistics, programme and procurement strategy should be considered in turn. Table 1: Benchmark rates at Q on GIFA basis Type BCIS Index 100 City of London Frame Low rise, short spans, repetitive grid/sections, easy-access (Building 1) /m /m 2 High rise, long spans, easy-access, repetitive grid (Building 2) /m /m 2 High rise, long spans, complex access, irregular grid, complex elements /m /m 2 Floor Metal decking and lightweight concrete topping 55-70/m /m 2 Precast concrete floor and topping 65-80/m /m 2 Fire protection (60 min resistance) 17-26/m /m 2 Portal frames Low eaves (6-8m) 60-80/m /m 2 High eaves (10-13m) /m /m 2 Table 2: BCIS rates for different locations, as 22 January 2016 Location BCIS Index Location BCIS Index Location BCIS Index Location BCIS Index Location BCIS Index City of London 131 Leeds 94 Birmingham 99 Glasgow 82 Liverpool 91 Nottingham 103 Newcastle 99 Manchester 96 Belfast 60 Cardiff 92

23 STEEL CONSTRUCTION COST 23 Cost Comparison

24 24 COST Cost Comparison Introduction The study compares two typical office buildings a business park office (Building 1) and a city centre office (Building 2) across a number of aspects for different structural solutions. It aims to provide a useful comparison for reference when considering the options available during the design and selection of a structural frame, and builds on previous comparisons by reflecting changes in construction techniques and structural frame solutions. Decisions on frame material and configuration are based on a number of factors not just cost so the study also considered the programme and buildability of each option, and included embodied carbon impacts for Building 2. Three independent expert teams scoped and delivered the cost comparison. Gardiner & Theobald provided cost information for each frame option Peter Brett Associates identified and designed representative framing solutions, and carried out the embodied carbon assessment Mace Group considered buildability, logistics and programme

25 COST 25 Building 1 A Typical Business Park Office Building Building: A rectangular three-storey business park office Location: Out-of-town business park Gross internal area: 3,200m 2 Floor-to-ceiling height: 2.8m Floor plate width: 18m External envelope: Brick outer skin supported by a steel angle off the slab edge with an inner leaf of cold-rolled metal studwork built directly off the slab Windows: 35% of façade Ventilation: Mixed mode Detail: One central core, 2nr lifts, one external metal escape stair. Floor-to-floor heights include for a 150mm ceiling and lighting zone and a 150mm raised floor zone Peter Brett Associates (PBA) established the structural grid at 7.5m x 9m, based on an optimum grid for a typical business park office not dictated by site constraints. Four frame types were considered: 1) Steel composite beams and composite slab 2) Steel frame and precast concrete slabs 3) Reinforced concrete flat slab 4) Insitu concrete frame with post-tensioned slab For all options the foundations were designed as unreinforced mass concrete pads. The core construction is steelwork cross-braced framing with a medium density blockwork infill for the steel options and concrete shear walls for the concrete options. For both steel options, the 30 minute fire resistance is provided by intumescent coating to beams and bracing members and boarding to columns. For the concrete options, the internal columns are plastered and painted for aesthetic purposes.

26 26 COST All options include a part-open and part enclosed roof plant area and lift motor room. The two steel framed options have a lightweight steel deck roof, while the concrete options continue the concrete slab construction of the lower floors. The floor-to-floor heights for the steel framed options include an 800mm service zone below the metal deck (300mm clear beneath the beams) and the concrete options allow for a 600mm services zone beneath the slab. Programme Comparison While cost is a key driver in decision-making when comparing alternative frame materials and configurations, programme and buildability impacts are should also be considered when selecting the frame material. Mace undertook the programming analysis for each option (see Figures 2 to 5) and to ensure a robust comparison, included preceding and succeeding trades to the frame elements. The programme durations for construction of the ground floor slab (two weeks four days), external façade (15 weeks) and internal works to a CAT A finish (18 weeks per floor) were assumed to be the same for each option. The study assumes the internal fit out starts on the ground floor and progresses up the building with three weeks between the start of the next floor an overall duration of 24 weeks for each option. The substructure duration was also considered in detail for each option. Both steel options required nine weeks due to the similar quantity of work, but to reflect the higher volume of groundworks, the reinforced concrete flat slab required 10 weeks three days and the post-tensioned option ten weeks. The programmes for the frame and upper floor construction are similar for both steel options. The precast slab requires slightly larger foundations than the composite option, but this is largely offset by the reduced number of steel members in the precast option. It is quicker to lay steel decking for the steel composite option because multiple numbers of decks can be loaded out at any time while the precast planks are limited to one per lift. However, this is offset by the time needed to stud weld each of the decks, which is slower than grout filling between precast planks. Both also then require a concrete topping. Ultimately, the advantages and disadvantages of each steel option largely cancel each other out, providing very similar programme periods for both the frame and overall construction. The steel composite option, though, provides the quickest frame and overall duration by one week, due to the speed of laying and distributing the steel decks.

27 COST 27 Figure 2: Building 1 Steel composite beams and slab frame programme Steel Composite 45.4 Groundworks and Slab 9 Steel Frame and Decks 6 Slab Pours Roof Works External Façade 15 Internal Works Figure 3: Building 1 Steel composite beams and precast concrete slab frame programme Steel + Precast Slabs 46.6 Groundworks and Slab 9 Frame + PC Decks Slab Pours Roof Works External Façade 15 Internal Works Figure 4: Building 1 Reinforced concrete flat slab frame programme Reinforced Concrete 48.6 Groundworks and Slab 10.4 Concrete Frame and Slabs Roof Works External Façade 15 Internal Works Figure 5: Building 1 Reinforced concrete frame and PT concrete flat slab frame programme PT Concrete Flat Slab 48.1 Groundworks and Slab 10 Concrete Frame and Slabs Roof Works External Façade 15 Internal Works

28 28 COST Programme comparison % difference from lowest +3% +7% +6% The programmes for the frame and upper floor construction are also similar for both concrete options, as the processes involved in constructing the structure are the same. The main variant is within the slab construction, with the post-tensioned option providing a slightly quicker duration because there is less reinforcement to place. It is also quicker to lay foundations for the post-tensioned option as the structure is lighter so the extent of excavation and concrete pouring to the foundations is less. Of all four options, the steel composite frame provides the fastest method of frame construction and overall programme for Building Time in weeks Steel Composite Steel Precast Concrete Flat Slab PT Concrete Flat Slab Logistics and Buildability Mace also undertook a logistics analysis for the frame options, and this has been reflected in total building costs through the preliminaries analysis. For both steel options construction is phased, with the excavation, foundations, drainage and service ducts, ground floor slab and erection of the steel frame and steel or precast decks occurring in four phases. A single mobile crane (c. 50t) is used for material distribution and loading as full perimeter access to the building is available, and the placing of concrete or structural screed to floors would use a concrete pump. For both concrete options construction occurs in two zones, each with three phases. The sequence includes the excavation, concrete foundations, drainage and service ducts, ground floor slab, reinforced concrete columns, formwork and propping for slabs, reinforcement or PT strands and placing of insitu concrete slabs using a concrete pump starting in zone 1 before zone 2. A tower crane located centrally on the building perimeter is assumed to be the most productive means of material distribution because it can distribute to both construction zones. The cost of the tower crane base has been included in the preliminaries costs, but there may be oversailing issues with a saddle jib crane.

29 COST 29 Cost Comparison Gardiner & Theobald provided the original and updated costs for the study based on market testing and recently tendered projects. The costs in Table 3 are all at Q prices, and exclude fees, VAT, project contingency and FF&E/AV allowances etc. They are based on construction in the City of London to allow direct comparison with Building 2, but they can be adjusted for different locations using BCIS location factors (Table 4). This page will be updated regularly by Gardiner & Theobald in the electronic version of this guide The study recognises the importance of considering all elements of the total building cost, not just the cost of the structure, as some elements are affected more by the choice of structural frame than others. The whole building cost rather than structural frame cost alone was therefore considered with the substructure, roof and external cladding costs assessed individually for each option. Frame and floor comparison Key Costs per m 2 GIFA The impact of the construction programme for each option has been considered in the total building costs the steel options benefit from lower preliminaries costs because of their shorter construction programmes. Table 3: Building 1 rates at Q on GIFA basis (City of London BCIS Location) Steel composite Steel + Precast Concrete Slabs Reinforced Concrete Flat Slab Post-tensioned Concrete Flat Slab Substructure 67/m 2 71/m 2 86/m 2 80/m 2 Frame and Upper Floors 171/m 2 187/m 2 170/m 2 198/m 2 Total Building 1878/m /m /m /m 2 % difference from lowest +10% +16% /m2 GIFA (City of London) Steel Composite Steel Precast Concrete Flat Slab PT Concrete Flat Slab Table 4: BCIS factors for different locations, as 22 January 2016 Location BCIS Index Location BCIS Index Location BCIS Index Location BCIS Index Location BCIS Index City of London 131 Leeds 94 Birmingham 99 Glasgow 82 Liverpool 91 Nottingham 103 Newcastle 99 Manchester 96 Belfast 60 Cardiff 92 As Table 3 shows, the steel composite beam and slab option has the lowest total building cost. This option also has the lowest substructure costs of all frame options due to the lighter frame weight and the lowest roof cost due to the lightweight steel roof deck. The structural zone and floor-to-floor height, while not the lowest of all the options, does not raise cladding costs compared to the other options, as only the concrete post-tensioned flat slab option has a notably lower floor-to-floor height and reduced area of cladding.

30 30 COST Substructure comparison % difference from lowest +6% +28% +19% Conversely, the reinforced concrete flat slab option has the highest overall building cost, some 10% higher than the steel composite option. This option has the highest substructure costs because of the heavier frame weight, the highest roof costs and the highest preliminaries costs due to the longest programme. A review of the steel composite and concrete flat slab options also highlights the importance of considering total building cost when selecting the structural frame material during design /m 2 GIFA (City of London) Steel Composite Steel Precast Concrete Flat Slab PT Concrete Flat Slab The concrete flat slab option has a marginally lower frame and floor cost to the steel and composite option, but on a total building basis, the steel and composite option has a lower cost ( 1,878/m 2 compared to 2,070/m 2 ). This is due to lower substructure and roof costs and lower preliminaries resulting from the shorter programme. Total building comparison % difference from lowest +6% +10% +9% 2100 So on comparison of all four options, the steel composite beam and slab frame has the lowest overall building cost. This is followed by the steel and precast concrete floor slab option, with the two concrete options higher Summary The cost and programme analysis of all four frame options for Building 1 shows the steel composite beam and floor option has both the lowest cost and the shortest programme, followed by the steel and precast concrete floor slab option /m2 GIFA (City of London) Steel Composite Steel Precast Concrete Flat Slab PT Concrete Flat Slab The frame and floor cost for the steel composite framed option is similar to concrete but the overall building cost is 9% lower than for concrete. Taking an average of the two steel options and an average of the two concrete options, the steel option costs are 7% lower for total building cost. In addition, both steel framed options can also be constructed in a shorter time frame than for the concrete buildings on average over 5% quicker. This page will be updated regularly by Gardiner & Theobald in the electronic version of this guide

31 COST 31 Building 2 A Typical City Centre Office Building Building: An eight-storey L-shaped city centre office Gross internal area: 16,500m 2 Floor-to-ceiling height: 3.0m External envelope: Unitised curtain wall system in storey-height panels 1.5m wide with feature fins/solar control. Solid areas are lined with cold-rolled metal studwork, insulation and plasterboard. Ventilation: Four pipe fan coil air conditioning without natural ventilation Detail: Double height reception area, central core and internal secondary escape stair PBA established the structural grid at 7.5m x 15m based on experience of similar city centre schemes, and this was used for both of the following frame options: 1) Cellular composite beams and composite slab 2) Post-tensioned band beams and slab, insitu columns. Both options use CFA piles, with three to four piles per column pile cap. The core construction is steel cross-braced framing with a medium-density blockwork infill for the steel option and concrete shear walls for the concrete option.

32 32 COST Buildings of this type normally include a basement, but for continuity between the options, the buildings in the study are assumed to start from ground floor with no impact from any basement construction considered. The 60 minute fire resistance is provided to the steel framed option through intumescent coating to beams and bracing members and boarding to columns, while the internal columns of the concrete option are plastered and painted for aesthetic reasons. Allowances have been made in both options for a part-open and part enclosed roof plant area and lift motor room. The plant area is a fabricated steelwork portal frame with composite metal panel cladding and the roof decks for both options continue the floor construction of the lower floors. The overall floor-to-floor height for the steel option is 4.18m, which includes a 700mm zone for services distribution through the beams with 400mm diameter holes allowed at 600mm centres. The overall floor-to-floor height for the concrete option is 4.375m, which includes a 475mm clear zone below the concrete band beams for services distribution, as recommended by the Concrete Centre. Both options also include allowances within the floor-to-floor heights for a 150mm ceiling and lighting zone and a 200mm raised floor zone.

33 COSTS 33 Programme Comparison Mace s programming analysis for Building 2 looks at both the frame durations and the whole building construction durations. The substructure works start with the CFA piling, followed by excavation for the pile caps and lift pits. For the steel option, the structural frame is erected on a floor-byfloor basis with the steel decking installation, stud welding and concrete floor toppings following on. For the concrete option, the columns and walls progress as soon as the ground floor slab is cast, and each floor slab is constructed in two pours, with the concrete shear walls completed progressively with each floor. The durations for construction of the ground floor slab (four weeks three days), external façade (16 weeks) and internal works to a CAT A finish (21 weeks per floor) were assumed to be the same for each option. The internal fit out starts on the ground floor and progresses up the building, with a two week lag to the start of the next floor, giving an overall duration of 39 weeks two days for each option.

34 34 COST Programme comparison % difference +11% Time in weeks Steel Composite PT Concrete Flat Slab While the substructure and ground slab construction have the same programme period 20 weeks for each option, the steel frame has a significantly shorter frame and floor construction (16 weeks compared to 28 weeks for the concrete option), so the internal fit out can start earlier. This means the cellular steel option provides a significantly shorter frame construction and overall programme for Building 2 compared to the post-tensioned concrete option, with a saving of 12 weeks for the frame and eight weeks across the programme. Figure 6: Building 2 Steel composite beams and slab frame programme CellularSteel Composite Groundworks and Slab Steel Frame and Decks Slab Pours Roof Works External Façade 16 Internal Works Figure 7: Building 2 Post T band beam frame programme PT Concrete Band beam 80.3 Groundworks and Slab 20.4 Concrete Frame and Decks 28.3 Roof Works 5 External Façade 16 Internal Works

35 COST 35 Logistics and Buildability The logistics for both the cellular steel and post-tensioned concrete options are similar, with the substructure works progressing from the main core pile caps working out in two directions for both options. Both frames use a luffing jib tower crane of around 50m radius situated outside the building footprint, used for distribution of the steel frame and floor decking for the steel option and for reinforcement and formwork distribution for the concrete option. The luffing jib also helps to overcome the oversailing issues common in city centre locations. Pour 2 External Hoist The superstructure works for the concrete option progress in two phases with two or three pours required for the floor slabs. Pumps would be used to place the floor slab concrete for the post-tensioned option and for the lightweight concrete topping for the steel option. Both options use an external hoist for fit out material vertical distribution.

36 36 COST This page will be updated regularly by Gardiner & Theobald in the electronic version of this guide Frame and floor comparison % difference +14% /m2 GIFA (City of London) Substructure comparison % difference +6% /m2 GIFA (City of London) Steel Composite Steel Composite PT Concrete Flat Slab PT Concrete Flat Slab Total building comparison Cost Comparison The Building 2 cost study also considered whole building cost alongside frame and floor costs, with the substructure, roof and external envelope reviewed in detail, while basement costs were excluded from the study as a constant across all options. As the frame material choice also impacts on programme, the results of the Mace programme and logistics analysis were also included when determining preliminaries costs for each option. All costs in Table 5 are at Q prices and are based on construction in the City of London to enable direct comparison with Building 1. Key Costs per m 2 GIFA Table 5: Building 2 rates at Q on GIFA basis (City of London BCIS Location) Steel Cellular Composite Post-tensioned Concrete Band Beam and Flat Slab Substructure 77/m 2 82/m 2 Frame and Upper Floors 237/m 2 270/m 2 Total Building 2337/m /m 2 Table 6: BCIS rates for different locations, as 22 January 2016 Location BCIS Index Location BCIS Index Location BCIS Index Location BCIS Index City of London 131 Leeds 94 Manchester 96 Belfast 60 Nottingham 103 Newcastle 99 Liverpool 91 Cardiff 92 Birmingham 99 Glasgow 82 % difference +4% /m2 GIFA (City of London) Steel Composite PT Concrete Flat Slab

37 COST 37 Embodied Carbon Comparison Cost and programme are key criteria in assessing design options, but for many projects the comparative environmental credentials are also important, so PBA carried out an embodied carbon assessment for both frame options for Building 2. Embodied carbon covers the cradle to cradle carbon dioxide (CO 2 ) emissions over the whole life cycle of the building, including end of life considerations but excluding the operational carbon occurring during the building s use. Figure 8: Building 2 cradle to cradle embodied carbon comparison % difference +23% The study focuses on the emissions from the structural elements as they represent the main carbon differences between the options but as with the cost and programme comparisons, also considers the whole building. To ensure a balanced approach, readily available industry data on materials emissions from Target Zero and Concrete Centre publications have been used. Non-structural embodied carbon emissions are based on benchmark information and are consistent across both frame options. Transport emissions are based on the Department for Transport statistics for average length of haul per commodity and on Concrete Centre data on the average delivery distance of ready-mixed concrete to construction sites. kgco 2 /m Steel Composite PT Concrete Flat Slab In assessing the emissions from the construction and demolition activities on-site, UK Environment Agency data, the Mace construction programming information and an estimated period for demolition have been considered. Cost study End of life scenarios have been selected to reflect current practice, where 99% of the structural steel and 82% of the concrete reinforcement are recycled and 100% of the concrete is down-cycled to provide granular fill material. Cradle to gate v cradle to cradle Life cycle phases: Extraction Cradle Manufacture } } to gate Transport Construction Cradle to Maintenance cradle Replacement Deconstruction Reuse and recycling End of life scenarios Not all materials are the same Cradle to gate assessments do not consider end of life

38 38 COST Figure 9: Building 2 cradle to cradle embodied carbon comparison % difference +11% The results of the study are shown in Figures 8 and 9. PBA started by assessing the buildings in line with the cost study and using only Portland Cement for the concrete mix. This showed that the embodied carbon was significantly lower for the steel frame than that for the concrete frame the steel option had an embodied carbon over 23% less than the concrete option. kgco 2 /m However, as cement replacement is often used to reduce sustainability impacts, the embodied carbon was also assessed using 30% cement replacement with fly ash and ground granulated blast furnace slag. This level of cement replacement is considered to be reasonable without having a significantly adverse impact on construction programme because of increased curing time. Steel Composite PT Concrete Flat Slab In this case, the embodied carbon reduced to 184kgCO 2 /m 2 for the steel option and to 204kgCO 2 /m 2 for the PT concrete option. Though the difference between the steel and concrete options was reduced, it was still significant with the steel frame having around 11% less embodied carbon than the post-tensioned concrete frame. 30% Cement replacement Admittance (W/m 2 K) Thermal mass the facts Normal weight Lightweight Thermal mass is independent of framing material The thermal mass is provided by the concrete in the floor plate Admittance is the rate at which a material can absorb heat Admittance declines when concrete thickness >90mm All flooring systems have sufficient concrete depth Over a 24 hour diurnal cycle the performance of common steel and concrete flooring systems are comparable Thickness (mm) Article of interest: THERMAL MASS

39 COST 39 Summary The cellular steel composite option has both a lower frame and floor cost and lower total building cost than the post-tensioned concrete band beam option. On a total building basis, the steel option benefits from lower substructure costs due to the lighter frame weight and a lower roof cost due to the cost of the steel deck compared to the post-tensioned slab. The steel option has a lower floor-to-floor height (4.18m compared to 4.375m) which results in around a 5% lower external envelope cost due to the smaller area of cladding and also has lower preliminaries costs due to its shorter programme. This contributes to its lowest overall total building cost. This page will be updated regularly by Gardiner & Theobald in the electronic version of this guide Overall, the frame and floor cost of the steel option is 14% lower than the concrete option. The total building costs for the steel option is 4% lower than the concrete option due to the frame and upper floor costs, as well as smaller foundations, a lightweight roof, a lower storey height reducing cladding costs and reduced preliminaries costs. Furthermore, the construction durations of the steel framed solution is shorter than the concrete framed one at 11% for Building 2. Over three key assessment criteria, the study has shown that the steel framed solution can outperform the concrete option and provide lower cost, a shorter programme and lower embodied carbon.