A refreshingly frank account of the trials and tribulations of opening roofs on large stadia came from the manager of the Cardiff Millennium Stadium at a conference on sports venues in Manchester last week. Geraint Evans regaled the audience with stories that must have been nightmarish at the time, but seem funny in retrospect. They partly stemmed from the fact that decisions to close the roof are generally taken the day before an event. This is not because closing the roof takes a long time (20 minutes), but because the acoustic and lighting rigs for big concerts take a long time to assemble. The result: heat fatigue.
It is not uncommon for rock audiences to be cooled down with water provided from the fire hoses in the complex. At one concert, 600 people in the upper stands had to be treated for heat fatigue.
On another occasion, as a result of a mix-up between the roof closing people and the pyrotechnic display staff, the fireworks were let off in 'open roof 'mode, when the roof was in fact shut. Result: scorch marks on the inside of the roof, and 10,000 spectators who could not see the first 15 minutes of the football game because of smoke.
To be fair, some of the problems stem from the tight budget, which provided assisted ventilation to the stadium in closed-roof mode, but certainly not air-conditioning.
Tetsu Hirata of Japanese construction and design group Takenaka made it all look simple with a wonderful video of a dozen stadia his firm has completed, all with opening roofs and air-con.
Manchester thought about it for its stadium, incidentally, but decided the £40 million cost in addition to the £110 million budget was too much. Actually, if you do the sums the payback is not too great over 10 years, assuming regular arena/concert hall use. You do have to take into account running costs, which at Cardiff are about £150,000 per annum.