Cost of structural steelwork
Cost is a fundamental consideration in the selection of structural frame material and form, which is a key early decision in the design process. This selection should be based on project specific costings, and the challenge to the cost consultant is to recognise and reconcile fluctuations in material prices in relation to returned tender price data all in the context of limited available design information during early estimates.
This article outlines a number of key cost drivers that must be considered in order to make steel frame rates project specific, and provides guidance on current cost ranges for different building types and locations. Through the identification of the key factors relevant to each project and the adjustment of typical rates accordingly, the accuracy of budget structural steel estimating can be significantly improve.
For most projects, the decision on the frame material choice and form happens early in the design process, often on the basis of early design principles, limited information and budget costings. Once selected, the frame material is unlikely to change, as to do so can have significant programme implications from the consequential impact on the design of other major elements, such as cladding, service installations etc.
While the decision on frame type for most developments will not be based on cost alone, it is nevertheless a key consideration in the decision making process and it is vital to support informed decision making with realistic cost information at this early stage, before refining during the detailed design stages. This is a challenging task as the cost of structural steel may fluctuate through the economic cycle, and reconciling material price information with returned tender prices is not always straightforward. Steel frame costs are also heavily affected by project specific key cost drivers, such as programme, access, spans and building form, making accurate adjustment of recently tendered rates or cost models difficult.
For those with limited previous experience of steel framed construction, the unique characteristics of the sector may not be immediately apparent. Anecdotal stories point to design decisions being made on the basis of non or poorly adjusted historic steel rates, suggesting that the complexities of the industry and the significance of key cost drivers are not necessarily widely understood.
Steel’s high market share of just under 70% and a review of recent industry trends highlights the importance of maintaining current, market tested cost advice for structural steelwork. Through a consideration of a number of key factors and consultation with the market and supply chain, budget structural steel estimating can be quickly and successfully tailored to specific projects.
The importance of realistic steel pricing
As the selection of frame material is a key design decision and impacts on so many related building elements – foundations, finishes, wall to floor ratio and cladding to name but a few – once the decision has been made and design has progressed, it is disruptive and generally abortive to make fundamental changes to the frame type or form. To do so would involve going back over design stages already completed and will involve most of the design disciplines. Where there is a programme to be maintained, this is almost impossible to achieve. Therefore, although the period of time to identify and select the best value frame is not a long one, it should not be rushed.
By its very nature therefore, the decision is commonly based on outline design proposals, with a limited amount of information available to the cost consultant.
Where the initial budget estimates of steel frame costs are not realistic, the wrong frame solution can be selected at a higher cost of not only the frame but potentially also the related building elements. It can also have an effect on buildability, logistics and the construction programme, as the frame construction is a critical path activity.
Making the most of the available information
At the early design stages of any project, cost models, benchmarks and historic cost data are key tools used by cost consultants in the estimating of all building elements. At this stage, elemental costs, including that of the structural frame, will usually be expressed as a rate per m² based on the Gross Internal Floor Area (GIFA).
Typical cost ranges for different frame types can be developed through cost models, and there are some indicative ranges given as part of this article, but how should one pitch the rate for any specific project?
Rather than arbitrarily using the highest rate of a range, it is key to interrogate and understand what those rates buy and how the standard ranges can be adapted to suit project specific factors. To do this most accurately, the cost consultant needs to ask relevant questions of the design team and to speak to the supply chain to use this information effectively. This will build a picture of the current and short term future market, rather than relying on indices to adjust benchmark or historic rates.
Key cost drivers
A number of factors can be considered to have a key impact on the price of structural steel frames. These ‘key cost drivers’ can be reviewed as part of the following groups:
- Function, sector and building height
- Form, site conditions and complexity
- Location, logistics and access
- Programme, risk and procurement route
Function, sector and building height
Different building functions across different sectors have varying typical frame costs due to their different usages of the created floor space. The usage of the building will influence the design loadings considered by the structural engineer and the building function will also result in different requirements for clear spans and floor-to-floor heights. This means that the average weight of the steel frame will vary between building types. For example, a low eaves industrial ‘shed’ building could have a frame weight of 40kg/m² GIFA, while a city centre office with a long spanning grid to avoid a forest of columns could have a weight of 90kg/m² GIFA.
A requirement for fewer columns will lead to longer spanning beams and heavier steel sections, which can increase the overall weight of the frame and therefore the cost range for the building. Clearly, these factors need to be considered when determining the rate for the structural frame for early estimates. Confirmation of the design assumptions and principles with the structural engineer is essential to clarify this.
It is also important to remember that the rate per m² is based on gross internal floor area, which will not account for variances in floor-to-floor heights. If for a specific project these are outside the normal range utilised in cost models, a higher or lower rate should be considered to tailor indicative rates to the project.
Form, site conditions and complexity
The complexity of the structure is closely related to building form and function, as well as specific site conditions. The building form will have an impact on the regularity of the structural grid, and the need to introduce non-standard sections, a wide range of different sections and connections in order to achieve structural stability.
Complex structural solutions, such as transfer structures, and fabricated beams may also need to be introduced to overcome project specific features or restrictions such as retained facades, adjacency of other buildings, ground conditions and so on.
The inclusion of non-standard sections will also increase the overall frame rate as fabrication costs are higher. Complex connection details may also impact on installation costs, tolerances and interfaces.
Location, logistics and access
The location of a project is a key factor in price determination and indices are available to enable the adjustment of cost data across different regions. The variances in these indices, such as the BCIS Indices, highlight the existence of different market conditions in different regions, which must not be overlooked.
Not only is the geographic location of the site an important consideration, site specific features also need to be reviewed. While the designed frame solution of two buildings may be very similar, the logistics and access arrangements will vary significantly between a city centre congested site and an easily accessible, isolated business park or industrial estate site, or even between alternative city centre sites.
Working in city centre or occupied areas can mean restrictions to working hours, noise, deliveries and craneage, all of which influence installation costs and can result in an extended on site programme. As the frame construction is generally a critical path activity, any increase to the construction programme will have an associated impact on project cost.
Programme, risk and procurement route
Accurate forecasts of steel frame costs are challenging due to the uncertainty of general economic conditions and the fluctuation of material prices experienced in the UK steel industry through the economic cycle. The form that the construction industry’s recovery from recession will take is a subject of deep debate among economists and industry commentators; clearly it will not be felt across all sectors and all regions in the same way.
One feature of the economic recession has been an increase in the relative prevalence of single stage procurement routes, particularly design and build, compared to the previously dominant two stage approach. This has aligned main contractor selection and price establishment more closely together and has increased the emphasis on ‘market pricing strategy’ where, while risks may be identified they may not be priced in to tender returns as cost has been further strengthened as the major determinant of contractor selection.
There were initial signs of improvement in the financial services sector in early 2011 and optimism that the commercial sector may begin to see returned demand. These largely failed to materialise and the economic outlook remained changeable through 2012. Even with forecasts of material prices continuing to rise over 2012 and into 2013, the relatively low position of demand in relation to capacity in the structural steel industry and continued intense competition in the construction industry generally, meant that contractor pricing strategies remained an important feature in securing work acting as a downward pressure on prices. It was not until the last quarter of 2013 that the commercial sector began to see returned demand and increased tender prices.
Components of the structural frame cost
In addition to understanding the cost drivers discussed above, it is also important to appreciate the different elements that make up the overall cost of the structural frame, their typical relative proportions and the interrelationship between them.
It is often assumed that a frame with the minimum tonnage will also have the lowest cost. However, as the figure (left) shows, the raw material cost typically accounts for only 30-40% of the total frame cost, with fabrication costs also accounting for 30-40%. For more complex frame designs, with higher proportions of non-standard sections, complex connections or specialist systems with higher fabrication requirements, the overall rate per tonne is likely to be higher than for a standard frame.
The construction of the steel frame typically accounts for around 10-15% of the total frame cost. It is therefore necessary to consider whether there are features of the proposed building that would significantly affect the erection cost as this will see a corresponding impact on the total cost of the frame. The extent of repetition, piece count, the type of connections to be used and access can all have a significant impact on the cost of constructing the frame.
This article seeks to give some current indicative cost ranges for structural steel frames for three key building types:
- Low rise and short span buildings, typically 2-4 storeys
- High rise and longer span building, typically 10-15 storeys plus basement
- Industrial buildings, split into low eaves of 6-8m and high eaves of 10-13m
All of the costs include allowances for a concrete core. The rates have been developed from cost models of the different building types and for each the average weight of the structural frame has been given.
As already highlighted, before using such ‘standard ranges’ it is important to confirm the anticipated frame weight and variables such as the floor-to-floor heights with the design team 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.
Low rise and short span buildings
Low rise buildings with a regular, short span structural grid are typical features of business park offices and teaching facilities. A key feature of these buildings is flexibility, particularly for speculative business park developments that need to appeal to as many potential occupiers as possible.
The buildings often need to be easily subdivided into smaller units and have large floorplates, typically are two to four storeys and have floor-to-floor heights of 3.75-4m. These buildings will typically have a uniform grid of 6-9m that provides largely column-free space and relatively high floor-to-floor heights.
The lack of complex steel structures needed to construct the regular grid contributes to keeping the average steel frame weight down, typically 50-60kg/m2 including fittings, but this category can cover a lot of building types and functions. This central assumption therefore needs to be reviewed with the design team. Due to the low rise nature of these buildings, the fire protection requirements are not as onerous as for high rise developments and 30-60 minute fire protection would be considered standard.
More detailed information on the key cost drivers for low rise and short span buildings is available in a related article on Cost planning - Education buildings
High rise and longer span buildings
High rise construction (10-15 storeys) is a typical feature of city centre construction. These buildings will often require longer structural grid spans to achieve more open space in the lettable floor areas, increasing the weight of the steel frame. To maximise floor-to-ceiling heights and increase flexibility for the building fit out, cellular beams may be adopted with openings through the web for the distribution of services.
City centre buildings are generally constructed on existing confined or irregular sites, which influence the building form and is likely to prevent the use of a regular column grid and may result in alterations to floor plates on the upper storeys.
All of these factors contribute to a higher average weight of the steel frame, typically 75-85kg/m² including fittings and, along with the increased complexity, result in significantly higher structural frame cost ranges than for the simpler, more regular low rise buildings.
The rate range given in the cost table below is generally applicable for buildings up to about 15 storeys; tall buildings above 15 storeys start to have fewer comparables in terms of benchmarks and are likely to have a much higher proportion of complex elements, non-standard sections sections and complicated logistics, especially when constructed on tight city centre sites. The rate range for tall buildings can be 15-20% higher than the top of the standard range.
More detailed information on the key cost drivers for high rise and longer span buildings is available in a related article on Cost planning – Multi-storey offices
Industrial buildings can cover a range of uses, including warehouses, non-food retail, science parks and distribution centres. The most common building form is a single storey warehouse with varying proportions of office space on a first floor mezzanine level. The traditional structural frame for an industrial building is a steel portal frame, as flexibility of the internal space is a priority, necessitating regular column spacings and long spans for a clear internal area.
There can be variants on the standard frame design, however. For example, a steel portal frame incorporating northlights would need consideration when adjusting the standard cost ranges. The use of a northlight frame can increase the frame cost by as much as 30%.
Fire protection requirements may also be considered as part of industrial building frame costs. The most common situation in which fire protection is required in single storey buildings is where it is necessary to satisfy boundary conditions; this is a project-specific factor that will need some liaison with the design team. Generally however, single storey buildings do not require fire protection.
Another key factor in determining the frame cost of industrial buildings is the storey height of the warehouse space. While the gross internal floor area may be the same, the weight of the steel frame of a high eaves, single storey industrial building will be higher than for a low eaves building, resulting in a higher overall frame cost per m² GIFA.
Typical structural steel frame weights for low eaves buildings (6-8m high) are about 30-40kg/m² overall of GIFA, including fittings and about 40-50kg/m² for high eaves buildings (10-13m high). However, ranges for high eaves buildings are generally wider than for low eaves buildings as they can have a much higher proportion of upper floor areas, across as many as 3 mezzanine levels; the frame rates for these buildings therefore need to be looked at carefully on an individual basis.
The cost table
The cost table summarises the structural frame costs of the three building types and also provides some indicative cost information on floor types and fire protection.
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.
|Type||GIFA Rate (£)|
BCIS Index 100
|GIFA Rate (£)|
City of London
|Frame||Low rise, short spans, repetitive grid / sections, easy access (Building 1+)||80 – 108 /m2||95 – 130 /m2|
|High rise, long spans, easy access, repetitive grid (Building 2+)||134 – 160 /m2||149 – 180 /m2|
|High rise, long spans, complex access, irregular grid, complex elements||154 – 180 /m2||175 – 200 /m2|
|Floor||Metal decking and lightweight concrete topping||43 – 61 /m2||50 – 70 /m2|
|Precast concrete composite floor and topping||48 – 65 /m2||55 – 75 /m2|
|Fire protection (60 minutes resistance)||7 – 16 /m2||9 – 18 /m2|
|Portal frames||Low eaves (6 – 8 m)||48 – 70 /m2||58 – 80 /m2|
|High eaves (10 – 13 m)||58 – 80 /m2||70 – 96 /m2|
(+ Building 1 and Building 2 refer to a cost comparison study)
To use the table:
- Identify which frame type most closely relates to the project under consideration
- Select and add the floor type under consideration
- 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:
£112.5 + £60 + £13.5 = £186 per m² GIFA
For other locations, the rates should be adjusted using location indices; the table provided contains a selection of indices as published and updated by the BCIS.
|Location||BCIS Index||Location||BCIS Index|
|City of London||112||Leeds||91|
Cost planning through the design stages
Main article: Cost planning through design stages
Once the early optioneering process is complete and the configuration of the proposed building has been established, the decision on the framing material has usually been made. However the design will not yet have progressed sufficiently to prepare detailed cost information on individual products and systems, necessitating the presentation of costs as a rate per m² of gross internal floor area (GIFA) based on the adjustment of typical cost ranges for similar buildings.
As the design develops and more information becomes available, the cost planning methodology changes and it is possible to quantify the key materials and test the initial allowances made at the outline design stages against the actual building. During the detailed costing of structural steelwork, a number of factors should be considered alongside the overall volume of materials, including the type of frame (for example, braced or continuous), steel product availability, the use of specialist systems, allowances for connections and fittings and the required fire resistance period and choice of materials to achieve it.
For a cost effective structural steelwork frame, minimum weight does not necessarily mean minimum cost. The most cost effective solutions achieve the best balance between the product cost and fabrication/erection time. For specialist systems such as cellular beams, shallow floors or steel bearing piles, the cost of the system itself should not be looked at in isolation. The costing approach should also consider the impact of the system on other elements such as fire protection, cladding, service integration and the overall construction programme.
Consideration of these key factors along with early consultation with the supply chain, or market testing, in particular with a steelwork contractor, can ensure that realistic costing of the steel frame and associated elements is maintained and improved as the design develops.
Cost comparison study
Main articles: Cost comparison study
In November 2011, the BCSA and Tata Steel commissioned Gardiner & Theobald (G&T), Peter Brett Associates (PBA) and Mace Group to undertake an impartial study of current construction practice for multi-storey office construction to provide cost and programme guidance for Quantity Surveyors and design teams. The study builds on previous comparisons to reflect developments in construction techniques and changes in prevalence of different structural frame solutions.
As decisions on frame material and configuration will be based on a number of factors, not simply cost, the study also considered the programme and buildability implications for each option.
PBA identified and designed representative framing solutions for two typical office buildings:
- Building 1 - A business park office
- Building 2 - A city centre office
G&T provided cost information for each frame option and Mace considered buildability, logistics and programme. PBA also carried out a cradle to cradle embodied carbon assessment on Building 2. The costs are regularly updated by G&T to keep the study up-to-date and relevant.
The study illustrates that for both building types, on a like for like basis steel framed solutions are highly competitive, with the frame and upper floor costs for the steel framed options being potentially up to 9% lower than for concrete. The study has also highlighted the importance of considering total building cost not just structural frame cost, as the choice of the structural frame material and configuration will have associated impacts on many other elements, including the substructure, roof and external cladding.
The total building cost for the steel options are on average around 5% lower than the concrete options as a result of the frame and upper floor costs noted above and smaller foundations, lightweight roofs, lower storey heights reducing cladding costs and reduced preliminaries costs.
|City of London costs||Steel Composite||Steel + Precast Concrete Slabs||Reinforced Concrete Flat Slab||Post Tensioned Concrete Flat Slab|
|Substructure||£56 /m2 GIFA||£60 /m2 GIFA||£72 /m2 GIFA||£67 /m2 GIFA|
|Frame and Upper Floors||£150 /m2 GIFA||£164 /m2 GIFA||£157 /m2 GIFA||£162 /m2 GIFA|
|Total Building||£1,613 /m2 GIFA||£1,643 /m2 GIFA||£1,716 /m2 GIFA||£1,696 /m2 GIFA|
|City of London costs||Steel Cellular Composite||Post Tensioned Band Beam and Slab|
|Substructure||£60 /m2 GIFA||£64 /m2 GIFA|
|Frame and Upper Floors||£208 /m2 GIFA||£228 /m2 GIFA|
|Total Building||£1,958 /m2 GIFA||£2,026 /m2 GIFA|
Furthermore, the construction durations of the steel framed solutions are also shorter than the concrete framed buildings (up to 7% for Building 1 and 10% for Building 2).
As mentioned, The study also considers embodied carbon, an element often overlooked as part of recent comparisons, but which is projected to become an increasingly important criterion for design options moving forward. The study shows that in this area as well, steel framed solutions have a noticeably reduced embodied carbon compared to the concrete solutions, with an 10-20% lower embodied carbon total for the cellular steel option than the post tensioned band beam option for Building 2.
Steel continues to be overwhelmingly the structural framing material of choice for multi-storey non-residential buildings, according to the latest survey from independent market research consultants Construction Markets.
The survey, commissioned by BCSA and Tata Steel, is the latest in a series going back to 1980 and is thought to be the biggest of its type in the UK, involving 750 interviews with construction specifiers. The results show that steel frames continue to have a dominant 66.8% share of the multi-storey buildings despite the difficult market conditions that all in construction are enduring. The survey also shows that the market grew by 7.6% in 2014, with overall floor area constructed in all multi-storey buildings increasing to 8,583,000m². Whilst this is promising, it is still only 56.2% of the size of the market at its peak of 2008, when it was 15,266,000m².
Headline figures for the market share in the total multi-storey buildings market:
- 66.8% - Steel
- 20.0% - Concrete
- 7.4% - Load bearing masonry
- 2.7% - Precast concrete
- 3.0% - Timber
The survey also shows that steel now has a 67.3% share of the multi-storey offices market, and a 66.6% share in the ‘other multi-storey buildings’ sector, which includes retail, education, leisure and health.
- Steel Construction - Cost, November 2014
- Steel Insight 1 – Structural steelwork, October 2011, Building Magazine
- Steel Insight 2 – Cost planning through design stages, January 2012, Building Magazine
- Steel Insight 3 – Comparative cost study - Multi-storey offices, April 2012, Building Magazine
- Steel Insight 4 – Cost planning of steel-framed multi-storey buildings, July 2012, Building Magazine
- Steel Insight 5 – Education buildings, October 2012, Building Magazine
- Steel Insight 6 – Industrial buildings, February 2013, Building Magazine
- Steel Insight 7 – Healthcare, April 2013, Building Magazine
- Steel Insight 8 – Multi-storey commercial buildings, July 2013, Building Magazine
- Steel Insight 9 – Cost planning structural steelwork, November 2013, Building Magazine
- Steel Insight 10 – Key frame cost drivers, May 2014, Building Magazine
- Steel Insight 11 – Cost update and case studies, November 2014, Building Magazine
- Cost planning through design stages
- Cost comparison study
- Cost planning - Multi-storey offices
- Cost planning - Education buildings
- Cost planning – Industrial buildings
- Cost planning – Healthcare buildings