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Lofty ambitions: 25 King goes up down under

Words:
Stephen Cousins

A tower in Brisbane by architects Bates Smart is a lesson in engineered timber construction and off-site fabrication

Bates Smart’s 25 King, Brisbane, Australia, is hybrid in form - a timber tower with a ground floor concrete frame.
Bates Smart’s 25 King, Brisbane, Australia, is hybrid in form - a timber tower with a ground floor concrete frame. Credit: Tom Roe

Australia’s tallest timber building, a 45-metre high office in Brisbane, was built in just 15 months using an off-site manufactured structure of glulam and cross-laminated timber (CLT).

The  ground plus nine-storeys tower, known as 25 King, was designed by Australian practice Bates Smart for Lendlease. It forms part of the AU$2.9 billion RNA Showgrounds redevelopment site near Brisbane's central business district. The structure is actually a hybrid: a concrete frame on the ground floor provides support for nine floors of 100 per cent engineered timber offices above.

The office floors are set out on a six metre by eight metre grid of exposed glulam columns, with diagonal members used for cross bracing, infilled with CLT walls and flooring. (The 45m refers to the nine floors of timber structure only.)

A colonnade of exposed glulam v-columns at ground level acts as bracing and transfers loads from the timber grid to the concrete structure. The colonnade provides shaded space for cafes and restaurants.

The timber frame is open to view through the glass facade, while the use of CLT ceiling soffits has eradicated the need for a suspended ceiling system and created a warm interior aesthetic with softer acoustics.

There were key structural and on-site benefits to using engineered timber for the project. A focus on pre-construction design and off-site fabrication significantly shortened the construction programme and minimised waste, with all openings required for services set out prior to manufacture.

Basil Richardson, studio director at Bates Smart, told RIBAJ: 'The construction programme was significantly reduced by the speed and efficiency of the timber assembly and the reduction in overall building weight enabled smaller concrete footing sizes. The entire frame was installed by a team of six to eight workers and weatherproofing was quicker because the facade was erected just one floor behind the frame.'

  • Office floors are set out on a six metre by eight metre grid of exposed glulam columns at Bates Smart’s 25 King timber tower, Brisbane, Australia.
    Office floors are set out on a six metre by eight metre grid of exposed glulam columns at Bates Smart’s 25 King timber tower, Brisbane, Australia. Credit: Tom Roe
  • Diagonal members used for cross bracing on Bates Smart’s 25 King timber tower, Brisbane, Australia.
    Diagonal members used for cross bracing on Bates Smart’s 25 King timber tower, Brisbane, Australia. Credit: Tom Roe
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When asked if there were any drawbacks to building so high in timber, he added: 'Ten storeys is a comfortable height for mass timber structures where there are efficiencies in the structural system.'

The circa 6,270m3 of engineered timber used on the project was all responsibly sourced and cut embodied carbon by 74 per cent compared to an equivalent conventional reinforced concrete building, mainly thanks to the CO2 sequestered in the wood.

25 King is expected to achieve a 6 star rating under the Green Star sustainability rating system, a 5 star rating under the National Australian Built Environment Rating System and a WELL Platinum rating.

Other sustainable features include rainwater harvesting, energy efficient lighting, optimised air-conditioning and a green wall in the entrance lobby.

The world’s tallest timber tower is the 18-storey Brock Commons student residence at the University of British Columbia in Canada. There are plans in Europe to go even higher: the HoHo Tower in Vienna will rise to 24 storeys (84 metres) when it completes in the next few months.  

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