Full steam ahead for venue

Its roll of honour runs through the famous performances by the Rolling Stones, Jimi Hendrix, Jefferson Airplane and the Doors' only British appearance to Oh Calcutta!, Peter Brook's Tempest and Tony Richardson's Hamlet, the last two being routinely described as "legendary".

Since we all know that if you can remember that decade, you weren't there, we can only assume that "legendary" here means "something fantastic just beyond the horizon of recollection".

Now it is about to start a new phase of its life. It is reopening on 1 June as a performance space after a quarter-century in underfunded limbo, during which it has been designated a Building at Risk by English Heritage, and plans to make it a centre of black theatre or the home of the drawings collection of the Royal Institute of British Architects have foundered.

Refurbished and extended by the architects John McAslan and Partners, it will be a venue for theatre and most kinds of music.

It will allow audiences of up to 1,800 seated and 3,000 standing and, thanks to flexible seating, performances both in the round and end on.

A new wing curving round its north flank will house a 120-seat studio theatre, a cafe, bars, box office and offices.

Its Piranesian brick-vaulted basement will house Roundhouse Studios, a set of rehearsal rooms and studios, with video editing and production equipment, and the Hub, a "social and performance area".

Each year the Studios and the Hub will, says the Roundhouse, "provide opportunities for up to 10,000 young people aged between 13 and 25 to develop skills and explore their creative potential".

This ever-precarious building now looks more secure than at any time since it was first built, thanks to a 10-year effort by its chairman, Torquil Norman, whose Norman Trust bought the building in 1996, and funding from Norman, the National Lottery and other sources to pay for the (remarkably low) £29.7 million development cost.

Norman's fortune is built in part on the outrageously kitsch Polly Pocket toys for little girls; he has now amply repaid his debt to culture.

But renovation brings its challenges. In the Sixties its power must have come in part from the very perversity of mounting Shakespeare and the Stones in a place made for trains, in the fragility of this halfruin, and in the quality of the Roundhouse as a gigantic found object.

Like medieval Italians amid the hulks of ancient Rome, the excitement lay in camping, and camping it up, in the ruins of Victorian industrial civilisation.

No sane person would design a theatre this size or shape, but now sanity must play a part.

Building regulations and business plans have to be followed, and funders' requirements met.

There will be no smoke, not even of tobacco. The Roundhouse has to grow up a little, become a little more respectable. It has to be something other than it was, yet still retain the sense of possibility that made it so compelling.

In McAslan's renovation this sense of possibility remains. The dominant feeling in the still-empty building is not of perfection, but of something about to happen, of an incompleteness that will only be made complete by events and audiences.

McAslan's approach is to be simple and deferential, with plain surfaces of plaster, concrete, steel and glass. The original Roundhouse is allowed to be the star.

This incompleteness is, perhaps, more than McAslan would have wished, exaggerated by the low budget and project managers who seem to have made glazing, ducting and steel details less crisp and more basic than their architect intended.

There is artistry to the incomplete, and skill in spending little, that here is sometimes substituted by the plain clumsy.

And, if one were to be really demanding, one might ask for some subtle intimation in the new work of the theatrical quality of fantasy which, somehow, is present in the coliseum/gasometer/Pantheon hybrid that is the original engine shed.

This would not be to make the place into some rouged thespian, but to impart a feeling of the fragile, the transient, or the illusory. There is something a little too matter-of-fact about the new additions.

The big story, however, is that one of London's great spaces has been brought back to life.

It has been done in a way that makes it believable that the raucous, the beautiful and the extraordinary will again flourish within its encircling wall.

The Roundhouse opens on 1 June with Fuerzabruta, a physical theatre show from the makers of De La Guarda, which runs until 30 July. Tickets: 0870 3891846, www.roundhouse.org.uk.