O'Donnell and Tuomey's transformation of Letterfrack Industrial School was the Irish entry at this year's Venice Biennale, which opened last Friday, writes Frank McDonald, Environment Editor

Exhibiting architecture has never been easy. Showing it on a world stage, such as the Venice Biennale, represents an even bigger challenge; it simply can't be done effectively by pinning drawings to a wall and placing a model of the project out front.

You also have to get with the theme, which this year's curator, Swiss-born architect Prof Kurt Forster, designated as metamorphosis, trendily shortened to "Metamorph". So what better project to represent Ireland than O'Donnell and Tuomey's transformation of Letterfrack Industrial School?

The partly-realised plan to turn it into a furniture college was chosen by Shane O'Toole, Irish commissioner for this year's biennale, because he was struck by the fact that "some buildings have savage histories that can leave a place in need of a kind of architectural exorcism, a project of redemption".

As he explains in the catalogue, the industrial school was built by the Christian Brothers as part of a nation-wide programme of penal reform, a place to incarcerate errant children from the slums. The harshness and cruelty of this regime became "one of the social scandals of modern Irish society", he says. But the people of Letterfrack were now "re-imagining their village and the institution at its heart" to secure a future in the new millennium. And through the community-owned Connemara West rural development company, this once notorious place is now home to Letterfrack Furniture College.

It also houses a local radio station, a library for both villagers and students and a farmers' co-operative. Students lodge with local families, bringing new life into the area. Meanwhile, O'Donnell and Tuomey's work is transforming the site by adding new buildings, which seem almost bent to the wind.

The next phase, as O'Toole says, should see the "forbidding symmetry" of the old building erased by removing the mean-looking porch, relocating the entrance to one of the gables and lowering the window cills to let people look out, while the exercise yard to the rear becomes an "academic garden".

All of this, as well as Letterfrack's grim institutional history, is represented by the Irish Pavilion at this year's Venice Biennale, which was opened last Friday with a stunning performance by artist and writer Gerard Mannix Flynn, who spent 18 months of his life in Letterfrack. Nobody who was there will easily forget it.

Located within one of the long buildings of the Arsenale, it is more installation than pavilion. A timber-framed structure representing the new machine room is topped by a vast colour photograph showing Letterfrack in its context, with a "Scary House" to one side and a modern settle bench on the other.

Sheila O'Donnell and John Tuomey's first joint project was another Irish Pavilion, at the 1990 "11 Cities, 11 Nations" exhibition in the northern Dutch city of Leeuwarden. Ironically, too, it was designed to house 12 paintings by Brian Maguire on the theme of isolation and institution, loneliness and prison.

In 1994, when they were preparing to be interviewed for the Letterfrack project, John Tuomey bumped into Mannix Flynn and talked at length with him - in the Long Hall pub on South Great George's Street - about "the presence of the past, the need for radical change, the motivation for art and architecture".

Sheila O'Donnell recalls encountering the old industrial school on childhood holidays in Connemara and says it "left an indelible image on the mind's eye". Even in 1994, more than 20 years after it closed, they still found themselves dealing with "a building which oppressively embodied the spirit of its past".

So there was huge excitement locally when the timber frame went up in Letterfrack, a still roofless "dinosaur skeleton", as John Tuomey calls it, placed on a concrete platform. It was "most definitely the largest structure that had been built west of the Twelve Bens since the pier in Roundstone".

Now, with the first phase completed and the project becalmed by lack of further Government funding, participation in the 2004 Biennale is a vehicle to see it through. "Venice offers us a chance almost to complete the Letterfrack project, before completing it in Letterfrack," O'Donnell says in the catalogue.

They were in Venice in 1980 when Aldo Rossi's iconic Teatro del Mondo was towed in and tied up in front of the Dogana, opposite Piazza San Marco, and even saw Rossi himself entering it.

"We were architecture tourists, if you like, saw this little pageant going on. So we know what happens at Venice."

Tuomey says something of their installation at the 2004 biennale "retains the kind of unfinished, but all-possible, feeling that a bone structure gives you" and that those who visit the exhibition will get some sense of the potential of the project to structure the community. "That matters a lot to us."

Being in Venice matters a lot, too. As a showcase for architecture from all over the world, it is unrivalled.

The amount of stuff on show is simply staggering, with all the big names represented either in the various national pavilions in the nearby Giardini or in themed exhibitions at the Arsenale.

Two other Irish projects are also featured - Heneghan Peng's winning scheme for the Carlisle Pier in Dún Laoghaire and the proposed Centre for the Performing Arts in the Grand Canal Docks area, by Studio Daniel Libeskind. The former is in a special category for "hyper-projects", the latter in "concert halls".

Ireland has now been represented at three successive international architectural exhibitions in Venice - by Tom de Paor's peat briquette pavilion in 2000, Bucholz McEvoy's Limerick County Hall (2002) and now Letterfrack "Transformation of an Institution" by O'Donnell and Tuomey.

This year's has been the most ambitious. It could not have been realised with State funding alone - €25,000 each from the Arts Council and the Cultural Relations Committee - so developer Terry Devey stepped in with major sponsorship because he saw it as "a story that the world had to hear".

That it is told so well in such a place reflects enormous credit on everyone involved. One Italian veteran of the Venice Biennale was so moved and inspired by the Irish pavilion that he told everyone it was the one to see. So even though it didn't win the Golden Lion award, it has certainly made a big impression.

• The catalogue Transformation of an Institution: The Furniture College, Letterfrack/O'Donnell + Tuomey Architects is published by Gandon Editions. Another book on their work, Archaeology of the Air, by Kester Rattenbury, was published last week by Navado Press, Trieste