It will continue to be a rock music venue for up to 2,500 people as well as a theatre, for one thing. It will have no theatre pod dropped into it, but removable seating instead. Up on high will be a new, 400-seater music venue called "the Lid". And down below, in the previously scarcely-used undercroft, will be a "creative centre" for young people's arts, media and fashion workshops.

MacAslan's interventions and mostly transparent additions try as hard as they can to preserve the character of the great circular shed while making it work as a modern performance venue. In its way, the Roundhouse also needs to grow up. As with the Royal Exchange, everyone now knows that the place works - enough brilliant performers and directors have proved that. It is time to move up a notch. But both places will remain highly individual, highly focused, not for everyone. MacAslan quotes the director Thelma Holt, a Roundhouse pioneer in the 1960s: "the Roundhouse quickly spits out anything it doesn't like."

So the provisional becomes permanent, yet somehow the improvisational magic must remain. The Royal Exchange, I suspect, has probably got it right for today's directors and audiences. As for the Roundhouse, Holt is right: it lets you know its feelings soon enough.