Measuring carbon - a small practice perspective

Introduction

Structure Workshop is a small engineering design practice with a ?exible and collaborative approach based on technical excellence, material innovation and low-carbon outcomes. In response to the climate emergency, and as a signatory to the Structural Engineers Declare initiative, the practice has committed to minimising upfront carbon and maximising material utilisation in its structural designs, as well as encouraging retro?t and reuse wherever the opportunity arises. A key part of this commitment has been to integrate embodied carbon calculations into standard design procedures.

The impetus to measure carbon resulted from an ambition to have a better understanding of the environmental impact of our structural solutions. At the time, no structure-orientated carbon tools had been made freely available, but the IStructE publication How to calculate embodied carbon [1] and the University of Bath’s Inventory of Carbon and Energy (ICE) database [2] had made it possible for a small practice to develop a simple tool in house.

We took on this challenge and developed our own carbon calculator (Figure 1): an Excel spreadsheet that automates the calculation of embodied carbon to practical completion and to end of life, including modules A, B, C and D.

In addition to referencing the ICE data, the tool can be customised to include additional materials and environmental product declarations (EPDs). Our ambition is for the whole project team to use the tool and coordinate outcomes. To this end it also includes RICS elemental standards for cost analysis.

While it makes sense to prepare for a future where embodied carbon is either taxed or regulated, the immediate bene?t in quantifying carbon is to inform our thinking today. Once familiar with the tool and the concepts, it is a quick and simple task to calculate the embodied carbon for a project.

At Structure Workshop, ‘doing the maths’ has completely changed our preconceptions of what good design is, with the result that carbon e?ciency is now considered to be as signi?cant as cost or structural e?ciency. Consequently, the early consideration of carbon has become inseparable from the normal design process.

It is important to acknowledge that we still have a mixed order book: some projects that perform well in terms of carbon, and some that do not. Having access to the numbers, however, has created a practice culture of continuous improvement. The data encourages us to design out high-carbon materials where possible; and where unavoidable to try and maximise their impact and utilisation, durability, and performance.

Potential to reduce carbon

The following three case studies illustrate projects where the measurement of carbon has improved or informed our design approach. These serve to illustrate the hierarchy of build less, build clever, build e?ciently.

Build less/Reuse: Yorkton Workshops retrofit, London (with Cassion Castle Architects )

The original intention was to demolish and rebuild a series of dilapidated workshops in Hackney, north London (Figure 2). However, our willingness to survey and address widespread defects in the fabric unlocked the possibility of retention for the client. In the end, it was possible to save almost all the existing structure. This both retained the character and history of the building, and generated a huge saving in upfront carbon through reuse.

The repair of defective structures demands an understanding of the fabric and a familiarity with typical defects associated with di?erent types of construction. Many small practices cut their teeth altering and extending existing properties at a domestic scale, which places us in an ideal position to in? uence a process such as this. Where previously the decision to retain or demolish existing structure was generally based on cost, the consideration of carbon is set to become more common in the future.

At Yorkton Workshops, the structure included two bays of Victorian construction, two bays of late 1980s steel construction and a central bay of makeshift in?ll. Brick repairs, enhanced restraint, and a ring beam stabilised the old stock brick walls, and a back analysis of the steel frame allowed us to increase the utilisation of the steel frame (Figure 3).

The central bay was judged beyond repair, but its demolition and rebuild provided an opportunity to recon?gure the entrance and circulation, making the plan more e?cient. The use of visual concrete in this location was considered acceptable due to the overall carbon savings made elsewhere. In its use, the carbon was minimised using ground, granulated blast-furnace slag (GGBS), and the material was expressed, maximising its impact, and providing the building with a strong contemporary identity.

For Yorkton Workshops, the total calculated upfront embodied carbon(modules A1–A5) was 74kgCO2e/m2 (Figure 4), compared with approx. 220kgCO2e/m2 for an equivalent new-build scheme using a steel frame with timber ?oors and concrete slab. This demonstrates the huge saving in carbon that can be achieved by prioritising retro?t over new build.

The project won both the Workplace under 2000m2 award and the overall Retro?t of the Year award in the Architects’ Journal Retro?t Awards 2021.

Build clever: Quarry House, Stoke-on-Trent (with Studio Bark)

Quarry House is a new house on the site of a disused quarry which is being designed to be net zero carbon over its lifetime, as well as demountable by hand and removed without trace after 50 years. The superstructure will be constructed using U-build, a self-build construction system that Structure Workshop has developed in collaboration with Studio Bark over several years (Figure 5). The U-build system uses zero-added-formaldehyde plywood, CNC cut to form boxes which can be bolted together to form orthogonal structures. At end of life, the boxes can be dissembled (?at-packed if necessary) and reused, according to circular economy principles. The typical upfront embodied carbon of the system is approx. 60kgCO2e/m2.

A standardised approach to self-build is not new and was pioneered in the UK by Walter Segal in the 1970s, with several of these timber-framed houses still to be found in south London. These are instructive to an engineer for their minimal material use, the simplicity of their detailing, and their approach to performance. The houses are well loved and have survived 50 years despite their rather ?exible construction and being founded on simple paving slab foundations. Notwithstanding their obvious success, they would clearly not comply with building regulations or the timber code today.

Inspired by this precedent and in an e?ort to eradicate concrete from the project, we compared a series of alternative suspended ?oor and foundation systems for Quarry House (Figure 6). Unsurprisingly, the solution with the highest upfront carbon was one of the most conventional: a steel-and-concrete suspended ?oor on mass concrete pads. The solution with the lowest upfront carbon was less conventional and uncodi?ed: a timber suspended ?oor on pads constructed out of old tyres ?lled with crushed stone.

As part of the study, we also rated how predictable we estimated the long-term performance of each solution to be, to allow the client to make an informed decision about their ambitions for net zero carbon against compromises that might be required to get there. The upfront embodied carbon for the ?nal structure is shown in Figure 7.

As engineers, we shoulder the risk of structural performance no matter the brief, and in a litigious world this typically results in high-carbon solutions (solid lumps of concrete in the ground tend to be both cheap and predictable). Historic structures such as the Segal self-build houses and the Victorian terrace (shallow footings combined with lime mortar) can be inspirational in this regard, and it seems there is merit in exploring ways to incorporate less conservative solutions, where appropriate, and to include and engage our clients in the decision-making process.

Build efficiently: Millom Ironworks warehouse, Cumbria (with IDK Architects for As If By Magic)

This example concerns one of several buildings forming part of a masterplan for the Millom Ironworks site in Cumbria. The warehouse has the rather fabulous brief of housing Europe’s largest collection of Airstream caravans and Gypsy vardos.

A competitive price and programme had been obtained to build a 16m span steel portal frame. When Structure Workshop o?ered to conduct a carbon study of alternative framing systems, we were pleasantly surprised that the idea was well received. Having developed the capability to calculate carbon and having promoted the thinking to the design team, we had created an opportunity to reduce carbon that had not existed before, along with an instruction to carry out the work.

The steel portal is a highly successful vernacular. Clear spanning, it is ?exible in use, cheap to build, quick to erect and robust. However, as a steel structure, it does not perform well in terms of carbon and the search for a competitive low-carbon alternative generated a lot of interest in the design o?ce. We developed various steel and timber solutions and carried out a detailed carbon assessment of each (Figure 8). Individual solutions were rated not only for carbon, but also for scalability, functionality utility, and aesthetics to obtain a balanced view.

A hybrid glulam-and-steel portal frame emerged as our recommended solution. This was not the solution with the lowest upfront carbon, but nevertheless halved the environmental impact while retaining many of the advantages of the traditional portal frame. The reasoning was that it is better to present a signi?cant saving in carbon that is adopted (and possibly repeated), than to present an ultra-low solution that is not.

In the event, the client, As If By Magic, having been presented with the numbers, was more ambitious. Given a clear opportunity to save carbon, it unhesitatingly instructed us to develop the three-pinned timber truss solution, i.e. the best performing in terms of carbon (Figure 9).

This project is still in design, but in considering the entire structure it is sobering to note the high carbon associated with the proposed concrete ground-bearing slab. Here we are faced with the common problem of how to avoid devaluing the advantages of a low-carbon superstructure by founding it on a high-carbon substructure.

Conclusions

Calculating carbon does not produce low-carbon solutions, but it does provide an awareness of the impact of our decisions, and it provides us with the means to improve.

What is surprising and gratifying is how our approach to design has been energised by measuring carbon, and how the activity has changed our preconceptions of what good design is. It is now di?cult to imagine not doing this as a normal part of the design process.

For us as a practice, the important step was simply to start calculating the embodied carbon in our structures. The positive e?ects seem to naturally follow.

Get the calculator

To request a free copy of the Structure Workshop Carbon Calculator, email [email protected].

References

[1] Gibbons O.P. and Orr J.J. (2020) How to calculate embodied carbon, London: IStructE Ltd

[2] Circular Ecology (2019) Inventory of Carbon and Energy (ICE database), V3.0 [Online] Available at: https://circularecology.com/embodied-carbon-footprint-database.html (Accessed: July 2021)