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May 2012 – Steel wins carbon comparison

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We reported last month on research showing that steel frames still dominate the market for multi storey and single storey buildings; this month we report on new research showing some of the reasons for steel’s continuing dominance, and suggesting why its market share is likely to grow.
The latest in the Cost Comparison Study series, which has just been published, shows once again that steel remains the most cost effective way to build modern offices, as well as being increasingly obviously the superior option when sustainability is important – which is of course always.

The study (see News) demonstrates the cost advantages obtainable by selecting steel – on average five per cent lower than concrete options, but there is a saving of up to nine per cent for the frame and upper floors when considered alone. Construction programmes are significantly shortened using steel, by 13% for the three storey office and 11% for an eight storey city centre office building. As well as the frames and floors themselves being cheaper, selecting a steel frame also provides savings from smaller foundations, lightweight roofs, lower storey heights, reduced cladding costs and smaller preliminaries costs.

What is new with this year’s study is the embodied carbon calculation, which showed that steel is convincingly superior to post tensioned concrete on this score as well. The overall study was carried out by quantity surveyor Gardiner & Theobald (G&T), consultant Peter Brett Associates (PBA) and contractor Mace. Cost information for each alternative was provided by G&T, with buildability, logistics and programming input coming from Mace and PBA designing the frames.
The study used designs of buildings of a type typical of those actually being commissioned in today’s market, and was very extensive, with four designs developed for the out of town building and two for the eight storey building.

PBA also carried out an embodied carbon assessment on the eight storey office building. This involved a cradle-to-grave assessment for carbon dioxide emissions, which included the carbon involved in producing the frame and constructing the building as well as considering what happens to the materials when the building is decommissioned. The recent Target Zero low carbon building design guidance project informed the calculation for steel emissions and published Concrete Centre data was used for the concrete calculations.

The difference between the two is striking. The steel building had embodied carbon content 23% less than concrete. Even allowing for the use of 30% fly ash and granulated blast furnace slag in the concrete mix rather than the standard Ordinary Portland Cement, which might be best practice but is not always what actually happens, meant steel still had some 11% less embodied carbon. Using steel piles for both options added to the foundation costs of both, but delivered a quicker substructure construction programme in return.

The steel sector has for long confidently argued that steel delivers an excellent sustainability performance, and the Cost Comparison Study is further proof of that case.

Nick Barrett
Editor

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