Highly Commended | Tackling Embodied Carbon Within the Retrofit of Historic Structures

As urbanisation in the UK accelerates, the construction industry’s reliance on high embodied carbon materials has become a major contributor to national carbon emissions. In response, this study explores strategies toreduce embodied carbon through the sustainable retrofit of an 18th-century building located on the author’s Major Study Project (MSP) site. The goal is to extend the building’s structural lifespan by incorporating low-carbon materials, thus aligning with the UK’s national decarbonisation targets.

The built environment is responsible for approximately one-quarter of the UK’s total carbon emissions. Despite this, much of the decarbonisation focus has been on new buildings, overlooking the vast number of historical buildings. Retrofitting these existing properties is essential as it avoids the carbon-intensive processes of demolition and new construction while conserving architectural heritage. By repurposing and upgrading older structures, we can avoid waste, preserve materials, and reduce the environmental impact of extracting and manufacturing new ones. The research is also closely tied to the author’s MSP, as it seeks to implement a sustainable retrofit solution for a historical building on-site.

To accomplish this, a mixed-methods methodology was employed over three phases. The first phase involved a qualitative literature review of 15 academic sources to analyse five structural materials: glulam, cob, steel,reinforced concrete, and Guadua angustifolia Kunth (GaK). These materials were evaluated for their embodied carbon across stages of production, transport, and recyclability. From these, three lower-carbon alternatives were shortlisted: glulam, cob, and GaK.

The second phase focused on creating 3D models using Autodesk Revit. These included five structural layouts: one replicating the existing material in the building, and four using glulam, GaK, cob, and a hybridcob wall with a timber frame. These layouts were scaled and designed in context with the existing structure,ensuring their architectural and structural feasibility. Each material was modelled realistically; for example, the GaK structure included a concrete footing based on prior studies highlighting its necessity for structural support and durability. This modelling phase set the foundation for quantitative analysis in the next stage.

In phase three, simulation-based research was conducted using OneClick LCA, a Revit-compatible tool that allows for life cycle assessment of embodied carbon. The focus was on key LCA stages, A1- A3 (production),A4 (transportation), and C2-C3 (end-of-life). The existing materials in the building were excluded from calculations since they had already been produced and would not add to future embodied carbon. For materials well-documented in databases, like glulam, data was pulled from UK-based Environmental Product Declarations (EPDs). However, for less common materials such as GaK and cob, where EPDs and product information are less commonly available, alternative EPD data from similar materials were used. This includes rammed earth as a substitute for cob and preserved bamboo products for GaK due to the lack of available direct data. Adjustments were made to account for local conditions such as transport distances.

Glulam also performed well in terms of sequestration, showing -25,257.90 kg CO₂e during production. However, its significant end-of-life emissions (18,682.21 kg CO₂e) eroded its net benefit. Cob, on its own, had lower sequestration at -14,912.60 kg CO₂e and even higher end-of-life emissions than the hybrid,resulting in a positive total carbon value despite a low transportation footprint.