Adaptability versus optimisation: a balance in the design of sustainable steel-framed building structures

In pursuit of a sustainable built environment, the construction sector faces a difficult decision: should building structures be optimised to minimise immediate carbon emissions or designed with reserve capacity for future adaptation? Optimisation reduces upfront impact but risks premature obsolescence, potentially leading to greater whole-life emissions. Design for adaptability aims to avoid such a fate. This thesis investigates where the balance lies for steel-framed buildings.

Through parametric structural design and embodied carbon assessment, this research quantifies the upfront environmental impacts of adaptability and the long-term consequences of optimisation across four key design parameters: imposed load capacity, vibration limits, storey height and structural grid arrangement. A clear hierarchy emerges – vibration capacity and grid layout incur the highest upfront premiums, while storey height and load capacity require more modest investments. These costs compound when strategies are simultaneously applied.

The initial designs were reassessed for two future scenarios: vertical extension and change of use. Adaptability proves valuable for vertical extensions only when future requirements can be accurately predicted; significant uncertainty potentially wastes the carbon investment. For changes of use, the optimal approach depends on which performance criteria changes – vibration-governed conversions favour adaptability, while load-governed scenarios typically favour upfront optimisation and future strengthening.

Incorporating time-value of carbon analysis reveals that the timing of adaptation plays an important role in the balance between adaptability and optimisation. Temporal tipping points establish a year of adaptation, beyond which the discounting of future carbon savings no longer justifies the upfront investment, promoting a design for future strengthening approach.

The thesis concludes that the preferable strategy of informed adaptability is governed by three critical thresholds: the nature, likelihood and timing of adaptation. A hierarchical decision-making framework guides practitioners through these considerations, supported by quantified evidence and analytical methods for evaluating time-value of carbon trade-offs in structural design.