Opinion
•Worship Square steel: a closer look
Exploring the key moves in producing an exceptionally low carbon structural steel frame
Worship Square is a distinctive new workplace situated in the South Shoreditch conservation area, alongside a new public square at the intersection of Worship Street and Clifton Street.
Our design replaces two six-storey, energy-inefficient blocks with one nine-storey, modern office building, centred around a high performance, lightweight steel structural frame. The design targets a BREEAM ‘Outstanding’ rating, WELL Platinum and NABERS 5* certification.
Steel is an energy intensive material to produce. We have worked closely with the wider design team and fabricator to track and optimise steel usage, and are happy to confirm the structure is 60% below the UK average for embodied carbon, due mainly to the high recycled steel content.
As the use of recycled steel in structures becomes more common, we also need to incentivise decarbonising primary steel production which will have a greater impact on global carbon emissions. Our carbon savings also rely on imported steel, highlighting the status of the British steel industry.
All the steel came from the UK, Europe and Turkey
Embodied carbon of Worship Square structural steel compared to the UK average
The project includes 922t of structural steel, accounting for 592t of CO2, giving an A1-A3 average carbon rate of 0.64kgCO2e/kg. This is 60% lower than the UK steel average (currently estimated by the BCSA as 1.64kgCO2e/kg).
The UK average is a balance of lower embodied carbon imported steel made from recycled scrap and higher embodied carbon domestic steel made from iron ore. Worship Square achieves this low steel average by utilising over 90% imported steel.
Illustrating the journey for the four largest steel sources, 94% of the structural steel
Over 80% of the steel used on the project was ArcelorMittal “XCarb” produced in Spain or Luxembourg. Although only 10% of the steel used was produced in the UK, this accounted for almost 40% of the embodied carbon. The remaining steel came from a mix of mills across Europe and Turkey. Although China dominates global steel production, making more than the rest of the world combined, none was used on the structure of Worship Square. This illustrates the relatively insular nature of the European structural steel market and the prevalence of recycled structural steel.
If 10% of the steel was produced in the UK, does this mean one beam in every ten? Possibly a particular shape not produced elsewhere?
Not quite – the structural elements are built up starting with stock universal beams and columns, using additional pieces cut from plate steel to create connection fixings, stiffening plates and other alterations. It is this plate which is the high carbon UK steel, whereas the stock beams and columns themselves are all low carbon imported steel. This additional plate steel for connections is not captured in design drawings, so we typically estimate it accounts for 10% extra carbon. This analysis indicates that for Worship Square, the added carbon was 9%, so our estimate proved fair. However, it also indicates that this added plate steel is a potential high carbon blind spot we should be more aware of going forward. Where reasonable we can take steps to reduce use of plate, for example rectangular openings are less likely to require stiffeners if located in the middle third of a beam.
To further reduce the embodied carbon, the most powerful change would be replacing the UK plate steel with a lower carbon option. Low carbon plate steel is available but must currently be imported, so this step would rule out British steel on the project. The UK steel industry has been a major employer and an important cultural symbol for over a century, and transporting material internationally also has a carbon footprint, so the industry must face this difficult choice.
DRI steelmaking is currently the only way for ore to bypass the blast furnace
EAF steel was used for beams and columns, with BOF steel added for stiffener plates and end connections
High scrap content steel reduces our project carbon footprint, however since demand far outstrips scrap availability, using it does not reduce the carbon footprint of the steel industry. To decarbonise the steel sector, novel technology such as Direct Reduced Iron (DRI) must be implemented when producing steel from iron ore. This technology uses lower temperatures than the prevalent Basic Oxygen Furnace method and is powered by natural gas rather than coal, giving a 40% embodied carbon reduction. In future the process can also be powered by green hydrogen, offering a route to zero carbon steel. We are seeking to use steel formed using a DRI production route on our projects as supply begins to increase.
Read more about addressing the environmental cost of structural steel:
For Worship Square we are very happy to have been able to deliver an exceptionally low carbon structure and are grateful to BHC steel and HB Reavis for working with us to make these insights possible.
As the industry matures we hope to use more steel produced through innovative lower carbon methods both in the UK and globally.
Photography by Make Architects and Heyne Tillett Steel
