Many companies can claim to have “strength and integrity” and never have to prove it. When you’re an engineer, however, there can be no question. Every project delivered must meet expectations – and over the many decades that follow completion.
With stronger sustainability targets seeing developers promise ever lower emissions, engineers are tasked with finding solutions that require less in materials and the embodied carbon they contain. The weight of those ambitions often fall on the engineer – their job is getting harder. But also a lot more satisfying.
In Sydney, global engineering consultancy BG&E shows it can be done.
Quay Quarter Tower leads major embodied carbon savings
BG&E is providing structural and construction engineering and materials testing services for its client AMP Capital on the 49-storey Quay Quarter Tower project, where around two-thirds of the existing structure has been retained and total floorspace almost doubled in a kind of “knitting” procedure to blend old and new.
Most importantly, reuse of materials has resulted in a carbon saving of more than 7500 tonnes.
Even though codes utilised at the time the Circular Quay landmark was constructed did not have any consideration for durability and design life, BG&E buildings lead NSW Vince Betro says rejuvenation and sustainability opportunities were highlighted by engineering studies. The latest techniques were used to test and assess the existing structural condition, validating existing materials and strengthening solutions could extend the structure’s life by another 50 years.
“There is a huge saving in embodied carbon by using the existing structure,” Betro says.
“We were able to demonstrate, with a lot of testing and re-analysis, that we could certify that whole building, including the existing structure, for another 50 or 60 years’ of life.”
To extend a building’s lifetime by 50 years by retaining a large portion of its existing structure was probably well beyond the imagination of the structural engineers who worked on the AMP Capital tower and others like it 40 or so years ago.
The expectations of today’s tenants, however, are vastly different. First, it has been efficient solutions that have promised much lower operating costs and much more pleasant environments in which to work, shop and live.
Alongside has been the rising demands from investors for their property portfolios to have ever stronger environmental social and governance (ESG) outcomes.
A chance to improve on the original is rare, and great for sustainability
A rebuild offers the chance to keep the essentials that still work well and improve on the original solution. A new build is something else. Today’s buildings are very different to last century’s stock. The use of post-tensioned concrete, with far lower embodied energy and carbon, allows for reductions in slab thicknesses and beam depths compared with reinforced concrete used in the old days.
“It translates to a lighter structure, which means smaller columns and lighter foundations,” Betro says.
The use of fly ash and ground blast furnace slag in concrete can see cement content cut by up to 25 per cent, he says, and aggregates such as blue metal can be partly replaced with “recycled” crushed concrete.
Modular construction techniques, where parts of floorplates, walls, entire bathrooms, for example, are built offsite can also see sharp drops in material used and in particular the usually huge quantities of materials wasted in on-site construction.
“We’re seeing a big trend in modular construction,” Betro says. “It’s all done in a factory, so there is quality control and much less wastage which translates to lower embodied carbon in the finished product.”
At Quay Quarter Tower the original 216 metre tall AMP building acts like a sundial at the northern end of the Sydney CBD. If it were pulled down for a rebuild, changes to regulations around overshadowing would have seen a much lower building approved, in consideration to the nearby Botanic Gardens.
The solution devised by BG&E was a refurbishment where larger floorplates have been oriented so that shading is no different than before.
Lavender Bay refurb of office to resi retains building fabric with clever redesign
Across Sydney Harbour at Blue, Lavender Bay, BG&E’s work to reconfigure a commercial building for residential use is a clear saving in embodied carbon. What made it possible is moving the concrete core from the perimeter of the building to the centre, to suit a residential layout.
When indoors, office workers want to see across a floorplan, but residents like to look out.
It’s timely work too.
At present property owners are casting fresh eyes over their portfolios and wondering if they might be left with a bunch of addresses no-one wants. They’ve seen office workers during Covid become increasingly picky about where they work and most will not be easily persuaded to go back to a second rate office.
Their bosses by contrast know that a first class office will not only be better at attracting talented staff in the war for talent but that premium rent in a fully upgraded or highly-rated Green Star building will be balanced by much lower utilities bills.
“As engineers, we want to play our part,” Betro says. “A project like Quay Quarter Tower will leave a legacy; it’s pushing the boundaries.
“We are also responding to what our clients are looking for. They want to work, live and play in buildings and structures that are sustainable, that are contributing to reducing carbon.”
Much of the built stock in our cities is destined to be reimagined. Any building conversion in this enlightened age will have to take a barebones approach to embedded carbon and emissions.