In an impressive engineering exercise, two office buildings in Brisbane were recently stitched together, maintaining much of the existing fabric while creating expansive floor plates for prospective tenants. It was challenging for the architects, Fender Katsalidis, and for the engineers Inertia Engineering. But the results will be a more sustainable product.
When you consider all the raw materials that go into a new building – and the carbon that’s emitted to produce them and transport them to site – the greenest buildings are usually the ones that are already standing.
But last century’s buildings don’t always meet the needs of today’s occupants. Modern office tenants, for example, want larger floor plates so that they can have all their employees buzzing about together on the same floor, Covid restrictions permitting.
This is the predicament Brisbane’s Midtown Centre project, owned by Ashe Morgan and DMANN Corporation, found itself in.
The inner-city site was occupied by a pair of dated office buildings, both formerly occupied by Health and Forestry, at 155 Charlotte Street and 150 Mary Street.
The project, worth around $500 million on completion according to media reports, involved turning the buildings into a single A Grade office tower.
Rather than knock down the two buildings and start again, the developers decided to merge the existing 20-storey structures entirely from top to bottom.
An additional six levels will rise from the slab on the 20th floor, making the new building 26 storeys in total, with generous 2400–2500 square metre floor plates.
The challenge to connect two existing buildings was no doubt a serious engineering feat for structural engineers, Inertia Engineering, and one that hadn’t been attempted before in Australia.
It helped that the two buildings mirrored one another so it was possible to match the two floor plates.
According to scientists involved in the project, opting for adaptive reuse rather than demolishing and rebuilding will save 37 per cent carbon emissions compared to a new build (a 11,000 tonnes carbon reduction in total), which is equivalent to running the building fully occupied carbon neutral for four years.
The builders, Hutchinson Builders, are also aiming for a minimum construction and demolition waste recycling rate of 90 per cent.
The office tower, which will be anchor tenanted by Rio Tinto and is due for completion in mid-2021, is also targeting 5 Star Green Star (Office Design and Office As Built), a 5 star NABERS Energy rating (Base Building) and Silver WELL (Core and Shell) certification.
Architect on the project, Fender Katsalidis director Mark Curzon, told The Fifth Estate that the Midtown Centre design was all about adaptive reuse.
“That’s the higher order of things, looking at existing buildings and understanding if they really need to be knocked down.”
Maintaining the historical significance of the area by modernising it was also important to the client, with the project including a restoration of the heritage-listed Charlotte Street facade.
As you might expect, a lot of analysis went into the physical act of merging the two buildings and how the services would work. The goal, Curzon says, was to create seamless continuous floorplates while maintaining the physical connection to the façade.
The existing lifts in the cores of old buildings were kept and new bathrooms for each floor hung onto the outside of the floorplates.
Instead of a centralised plant room, retaining the existing fabric lent itself to a floor-by-floor plantrooms.
Curzon, who was involved in the another floor-by-floor system that went into 100 Mount Street in North Sydney, says the underutilised building services model will be beneficial in a post pandemic environment where tenants will want to avoid cross contamination of conditioned air between floors.
The other advantage of distributed plantrooms, according to Curzon, is that it gives tenants more choice and control over how they heat and cool their workspace.
With a plant room on every level, it’s effectively a “plug and play” approach to heating and cooling that gives tenants more control over their energy use (and the look and feel – Curzon says creative might want to keep the ducts exposed to maximise roof height, for example).
With most tenants becoming more conscious of their environmental footprint, the expectation is that more choice and control over the airconditioning will prompt tenants to take off a layer of clothing instead of adjusting the temperature.
Curzon says that the refurbishment made the floor-by-floor model particularly attractive, and has also proved “incredibly successful” at 100 Mount Street, which was a new build.
Other ways the Brisbane building keeps energy use down is through a high-performance façade glazing, extensive use of terrace recesses and a faceted façade to minimise solar gain.
While the building has exceptional credentials on embodied carbon and energy efficiency, it’s not completely fossil fuel free and no announcements have been made about its carbon neutrality.
Another breathing building for Brisbane City Council
The building was also designed in line with the Brisbane City Council’s “Buildings that Breathe” guidelines for passive, subtropical design, which is gaining traction now that the council is offering incentives to developers.
In this instance, the developers were permitted to increase the floor space by opting for plenty of natural ventilation, operable windows and doors, an abundance of plants and ample outdoor space.
As such, occupants will have access to a sky garden on level 20, a landscaped garden terrace on top of the podium and “green seam” that encases the tower.
Curzon says the design are full of “mixed mode” spaces that will be the perfect climate in winter, allowing people to work and interact in non-conditioned spaces. Not only will this allow occupants to “really connect with nature”, it will also lessen the need for air-conditioning and reduce the reliance on lifts to go outside for fresh air, helping to curb energy use.
The landscaped areas across the development total in excess of 3000 metres square.