This was no facelift, but open-heart surgery on one of the world's busiest theatres and the most watched building in Australia – with every architect in the country looking over your shoulder, none closer than the eminent members of the Opera House's own Design Advisory Panel.

Completed in 1973, by 2012 the Concert Hall was facing end-of-life theatre machinery, a poor reputation for acoustics, and mobility issues that left some areas impossible for wheelchair users. The entire building – Jørn Utzon’s visionary architectural design and Peter Hall’s complex interiors and glass walls – is World Heritage listed; nothing could be touched in any way that showed. ARM’s repair and modernisation of the acoustics, staging and accessibility make it look like nothing has changed when what really took place was enormous.

Into an already jam-packed heritage structure, the renewal has made the venue more efficient, more equitable, and more democratic, while complementing the architectural brilliance of Utzon and Hall.

The result is a venue that turns from orchestral to amplified mode in a matter of hours, stages more shows with more diverse programming, and is finally, fully accessible. 

To realise ARM’s designs, 174 tonnes of new structural steel (equal to more than 100 cars) were installed, including 44 tonnes of hot pink steel to mark the difference between primary and secondary steel; 720 tonnes of new reinforced concrete placed; and 300 kilometres of cable laid. The stage was completely rebuilt with automated risers – the Sydney Symphony's horseshoe layout now deploys at the touch of a button. An invisible but operationally critical flying system was fitted to safely handle the demands of contemporary production.

Eighteen fushia-toned, petal-shaped acoustic reflectors above the stage make what clarinettist Chris Tingay says is the biggest change in 24 years playing here. Richly modelled timber panel box fronts add warmth and intricacy to the acoustic experience. Automated drapes flip the hall from acoustic to amplified mode – the Sydney Symphony one afternoon, a contemporary performance the next – with a speed and flexibility the building never had before. A new passageway and lift give wheelchair users independent access to the Northern Foyer and its harbour views for the first time.

We came to this project from Hamer Hall and the Shrine of Remembrance – two redevelopments that demanded the same discipline: understand the original authors, work in conversation with them, leave no scars.