Nestled amongst the charming streets of Yarraville, one of Melbourne’s vibrant, inner-city neighbourhoods, the heritage facade of this weatherboard cottage is emblematic of the historical context of the area. The perimeter of the dwelling is characterised by a graceful eucalyptus tree growing on the edge of the home’s recent addition – a gentle reminder of the importance of biodiversity in our urban environments.

This address is about to be transformed into a contemporary family home that aims to reduce operational embodied carbon by employing passive house principles, as well as showcase how early engagement with suppliers can lead to more sustainable outcomes.

The owners of the dwelling, Ed Bond and Harriet Oswald, are a structural engineer and architect duo who purchased the home for its structural integrity and the ability to entertain and house visitors from overseas. Originally from the UK, Ed’s extensive career spans commercial, residential and infrastructure projects across England, Dubai and Victoria. Ed is now a Principal at the Melbourne headquarters of Robert Bird Group, a globally renowned engineering consulting group. This endeavour gives him the ability to create something personal and considered, while working on megaprojects across the globe.

“I’m quite passionate about sustainability, and reducing the monetary impact of the build,” says Ed.

“So the project gave me an opportunity to explore how to do that, while embracing the freedom to design something I liked.”

Bond says that an architecture of sufficiency was of high priority, optimising space while remaining environmentally conscious.

“At the moment, Australia has the largest houses, pro rata, in the world,” he says. “There is a lot of space wastage so it was crucial for us to optimise the floor plan as a starting point, and really consider how much space we needed based on the home’s purpose.”

The environmental resolve underpinning the project was further augmented by the visit to a passive house, during the couple’s time in New Zealand. “It was in the middle of winter, and they were walking around in shorts and t-shirts,” Bond recalls affectionately.

“They also had very compelling data in terms of how little energy the home was using. That really shifted our focus when it came to our own build.”

Initially, the duo intended on stripping the home back to its bones in order to improve the thermal envelope, given the lack of insulation and potential of leaks. That turned out to be cost-prohibitive.

“We've modified our approach, which actually worked really well in an adaptive reuse,” Ed says.

“We’ve kept the plaster board and as much of the original house, built out and really improved that envelope with minimal disruption, which has allowed us to lock all the existing embodied carbon in.”

Driven by the importance of sustainable outcomes, Ed is not only hoping to reduce operational embodied carbon through passive house principles embedded in the thermal envelope, but also lower upfront greenhouse gas emissions. In order to help achieve that, he’s turned to Holcim, one of Australia’s leading suppliers of low-carbon concrete. Holcim’s low-carbon product, ECOPact, has been designed to offer up to 70 percent lower CO2 emissions compared to the Australian National Life Cycle Inventory Database benchmark (AusLCI).

While delivering a lower percentage of CO2 emissions, the ECOPact range can be used in a variety of structural components, such as foundations, columns, walls or driveways. It can also be handled, pumped and finished like conventional concrete.

Ed was familiar with Holcim’s low-carbon offering, and discovered more through CPD sessions at the Robert Bird Group Melbourne office.

“It seemed like a natural choice for what we were trying to achieve with our build,” he recalls.

From there, Bond was intrigued by the solutions the low-carbon product offered.

“I essentially asked them (Holcim) for the lowest embodied carbon concrete,” he says.

“The concrete slab is on the ground, and will be supported by piles in some locations. It has to perform its job in terms of bonding appropriately with the ground, but it's not suspended, which means it's not going to be working harder under its own weight. So I've considered what the structural performance requirements are, while keeping an open mind.”

The process – defined by robust engagement between Ed, Sushant Mane, Holcim’s Technical Manager in Victoria, and Dylan Viviers, Holcim’s National Specifications Manager – is aimed at designing a specific concrete that will push the boundaries of low-carbon concrete as well as have a percentage of recycled materials.

“The technology is the same as ECOPact, with the aim to push the CO2 reduction further,” explains Viviers. “This can be achieved through the reduction of the cement component, introduction of industrial recycling by-products and using different admixture technologies to ensure that all the performance characteristics are still met. In addition, instead of targeting a 28-day strength, we’re looking at a 56-day strength. Really, it’s about working really closely with Ed as the engineer.”

The development of the bespoke ECOPact mix has been made possible through early engagement between the homeowner and the concrete supplier. It allowed them to negate over-specification of compressive strength – and assume a progressive philosophy in embracing new techniques.

“The hope is the project can be used to demonstrate to the residential sector and beyond that low carbon outcomes can be achieved by embracing broader communication channels across industry,” Ed explains.

“More often than not, late engagement means that things don't happen. Especially in the sustainability space, where, if you're attempting to try something different, you need to have all parties involved from the start. In this case, everyone is on board, understands the material and how to work with it, as well as what it means to the project.

“The more future-forward thinking is incorporated in the early stages of the design inception process, the better and more enduring the final outcome is going to be. And, to me, that really is at the heart of sustainability – for it not to be an afterthought, but to be at the forefront of the design from the get-go. And that means engaging suppliers like Holcim.”

Ed adds that, in his experience, the industry works in silos too much. And that, he points out, can get in the way of maintaining an open mind and holistic mindset.

“It’s crucial for me to be competent in my own discipline as a structural engineer, especially when it comes to embodied carbon,” he explains. “But having that holistic mindset and being able to look beyond your scope, interfacing with different disciplines, is how you unlock more benefits for a project. And I'm a big believer in this multidisciplinary kind of thinking, which definitely applied to this project. Interconnecting all the different parties – from designers and engineers to contractors and suppliers – is key. As well as that early engagement.”

He adds that it's been a great experience of engagement between himself and Holcim, exploring how they can get to a really low, hopefully market-leading, embodied carbon outcome, particularly in the context of residential typology.

Just down the road from Ed’s plot, a robust hospital is undergoing a makeover, and is also using Holcim’s ECOPact. For Dylan, this is an important demonstration of the fact that the sustainable solutions aren’t there just for the multi-million dollar huge infrastructure projects. “They are there for the smaller-scale projects, for the homeowners and renovators, too,” he says.

Naturally, the embodied carbon is only one of the components of sustainable construction. “It's good to push towards the lowest possible carbon outcome, but it's not a complete picture,” Ed points out. “For instance, we've added embodied carbon for some of the piling we are going to do in order to retain this beautiful eucalyptus tree growing right on the edge of the property helping to protect the biodiversity.”

“Often, the approach is that biodiversity is removed, generating a less diverse landscape, and I think that's a big problem in the industry. We want to demonstrate that it's okay to take on these more challenging projects – and show how one can go about resolving some of these challenges.”

Holcim’s willingness to connect with architects, designers, engineers and homeowners early in the process – to both educate on the possibilities of their low-carbon products, as well as explore new avenues that can help create bespoke and better solutions – can certainly help address some of these issues.

Both Holcim and their client hope that the project will set a new standard for holistic, considered and environmentally-focused construction across the residential sector, proving the catalyst for more attainable, collaborative and inclusive sustainable construction for all.