The architects began to imagine how they could honour those values in a NZ$120 million (HK$777 million) extension and restoration of one of New Zealand's most cherished public buildings.

In partnership with Auckland-based architect firm Archimedia, they came up with a design that has just been awarded World Building of the Year.

The title, judged by a jury including Ken Tadashi Oshima of The University of Washington (chairman); Ken Yeang, formerly of Llewelyn Davies Yeang; Patrick Bellew, of Atelier Ten; Jeanne Gang, of Studio Gang Architects; and Dietmar Eberle, of Baumschlager Eberle, was awarded at the World Architect Festival in Singapore on October 4.

The project itself was won by the two firms after an international design competition in 2004. The extensive brief included restoration and adaption of existing heritage buildings; a new gallery extension that more than doubles the public exhibition space; extensive basement storage and support areas; and the redesign of adjacent areas of Albert Park.

Richard Francis-Jones, design director of FJMT, recalled feeling the weight of public scrutiny.

"It's a very sensitive site - a highly valued heritage building, with a beautiful and important park around it. There was a lot of concern about putting a new building there," he said.

"Our concept was to connect the gallery with the natural landscape, to create, through a series of beautifully crafted timber canopies, a building that was a little like a forest - transparent, open, and inviting."

This was to be realised through great skill and craft using native kauri. Challenges included naturally sourcing a precious timber that can no longer be harvested and finding enough specialist joiners who still practised traditional techniques.

But getting the scheme approved through a lengthy court process remains, in his mind, the biggest hurdle the team had to overcome.

Art galleries have a clear primary purpose - they are used to hang art. This can result in a functional, if somewhat sterile, built environment - the antithesis of what these architects had in mind. Instead, they envisaged a space that conceptually had no walls - and seemingly, little visible means of support - and this in a seismic zone, where buildings have to be earthquake-resistant.

Here technology entered the equation.

"A complex, three-dimensional double-curved roof profile was developed and tested through advanced computer- aided design techniques and physical models," Francis-Jones explained.

"The canopy design was then refined right down to the detail of fixings and actual board selection using full-size prototypes.

"The final form of these interconnected canopies transfers all the earthquake loads through its three-dimensional, truss-like forms, allowing the whole roof to balance with great lightness on finely tapering timber and steel posts."

Off site, joiners from Papakura Joinery began piecing together a series of 23 golden-hued, tree-like canopies, crafted from local kauri stock that was either recycled or forest-fallen. Individual planks were hand-planed, curved and clamped in the manner of wooden boat-building, then fitted together for a gentle, double curve. Later, the canopies would be craned on site, to rest above slender, timber-clad engineered steel columns.

Thus, the whole assembly appeared like a forest, just as the architects envisaged.

Natural light is normally a no-go in an exhibition space, but here it is abundant, with triple layers of glazing in the visually wall-free Park View Gallery embracing the views outdoors.

The idea of being so transparent is "in some ways a great irony for an art gallery", conceded Francis-Jones, but he added: "Being so open, transparent and connected with the landscape became a powerful metaphor for the project, as the landscape holds great meaning for Maori people, and projects a broader and inclusive sense of welcome.

"[From the park] you get the sense of seeing the artworks, and people moving about inside, without even having to go through the door.

"The more we can break down the threshold anxiety of going into a museum, the more people can freely be in touch with the great works that are part of New Zealand culture."

At the awards night Paul Finch, World Architect Festival programme director, remarked: "The winning project transcended category types … This is a major design achievement in a seismic zone … The resulting design is a rich complex of built ideas."

The project also won New Zealand's top prize, the 2012 NZ Institute of Architects' Architecture Medal, earning judges' praise for the building's relationship with its neighbours (in particular, Albert Park), and use of outdoor space, which "invites the public into the gallery".

Prestigious awards are one thing but, for the winning team, the real achievement came in September last year, when the gallery was reopened after a three-year makeover that was six years in the planning.

"We witnessed an instant response from the community - they felt a great sense of ownership and pride that this was their gallery," said Francis-Jones.

Architecture is like parenthood, he mused. You may nurture and guide, but you have to let your "child" grow on its own. And then you have to let it go.

For these guardians who have done their best, public acceptance is the reward.