Understanding Embodied Carbon Part 3: A Balance of Sustainability, Practicality and Design

Is larch cladding better than zinc? Should we be installing Solar PV on our new projects? As architects, we need to be considering all factors when it comes to improving the embodied carbon impact of our projects – but how far should we go?

For the next stage of our Understanding Embodied Carbon series, we are taking a look into our RIBA award winning project, The Garden Room at Cwm Barn, and analysing what worked well, but also what lessons we have learnt for improving the embodied carbon impact of our future projects.

Designed to integrate sustainability and functionality for a family space and located in a rural landscape, The Garden Room combines aesthetic appeal with an environmentally conscious approach. With a total embodied carbon of 614kgCO₂/m² GIA (below the RIBA 2030 standard), the Garden Room showcases the challenges and decisions that come with balancing sustainability in material selection with design choices.

Embodied Carbon in Focus

Embodied carbon measures the greenhouse gas emissions associated with the production, transport, and assembly of building materials. As the urgency to address climate change increases, reducing embodied carbon has become a key objective for architects and builders. Read more about embodied carbon in architecture in our previous blog, Understanding Embodied Carbon, here.

Key Features of The Garden Room's Sustainability Strategy

The building was designed using fabric-first principles, using a high-performance twin stud wall system, built off site by local contractor Firth Construction. The airtight and vapour breathable panels were fully filled with recycled newspaper insulation. As a result of this approach, the project betters the RIBA 2030 Climate Challenge target for energy in use and achieved an impressive airtightness result.

We used a combination of materials, selected not just for their aesthetic qualities and durability, but also their contribution to long term sustainability. The choice of materials of course, has a direct impact on the embodied carbon impact of the project.

Cladding

The structure features zinc as the primary external cladding material. Zinc was chosen for its durability and low-maintenance qualities – a key aspect of the client’s brief. However, the use of larch as an alternative would have reduced the embodied carbon by an additional 32 kg CO₂e/m² GIA. This difference is relatively modest and would likely be cancelled out over the lifetime of the building if the timber cladding was not properly maintained and had to be replaced. For this reason, Zinc was deemed to be the most appropriate cladding material in this case.

Photovoltaic (PV) Panels and Their Impact

Part of The Garden Room's specification was the inclusion of photovoltaic (PV) panels, which help generate renewable energy on-site for the main house as well as The Garden Room. Despite their operational benefits in terms of reducing reliance on grid electricity, PV panels are known to have an impact on embodied carbon due to the energy-intensive processes involved in their manufacturing.

Landscape photograph of The Garden Room from an elevated position so you can see the Solar PV panles on the roof, and the entire building in its setting

If PV panels had been omitted from the design, the embodied carbon calculation would have improved by a notable 104 kg CO₂e/m² GIA. This finding emphasises the importance of the "fabric first" approach, where reducing the operational energy demand of the building envelope itself (through insulation, airtightness, and passive design) can offer more sustainable benefits than relying on renewable technologies that carry their own carbon burden.

It's important to consider these elements in a holistic way and acknowledge the broader benefits PV panels provide. While they contribute to embodied carbon during production, PV panels generate clean, renewable energy throughout the building’s lifespan, significantly reducing operational carbon emissions. Additionally, PV panels can help future-proof the building against rising energy costs and reduce dependency on external energy sources, contributing to energy security and long-term sustainability. Therefore, while PV panels increase embodied carbon, they offer considerable long-term environmental and economic benefits that should not be overlooked.

Embodied Carbon Results

The final embodied carbon calculation for The Garden Room stands at 614 kg CO₂/m² GIA, compared to the RIBA 2030 target of 625 kg CO2e/m2 GIA, which reflects our careful consideration of materials, energy systems, and construction processes. While some aspects of the design could have been adjusted for even greater reductions, such as the exclusion of PV panels or using more timber cladding, the project showcases the complex decision-making involved in balancing sustainable goals with design intent and practicalities.

We can learn from The Garden Room how small design changes can make a significant difference to the overall embodied carbon of a building. By evaluating material options like zinc versus larch and considering the impact of PV panels, sustainability is about more than just operational energy savings—it's about considering the full lifecycle of the building materials and systems. This project underscores the importance of a fabric first approach while highlighting the trade-offs that are sometimes necessary in the quest for a low-carbon future.

Ultimately, The Garden Room stands as a thoughtful and sustainable design, pushing forward the conversation of embodied carbon in architecture.

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Building Stronger Communities Through the Southside Project