Special indoor environmental problems occur when the movable roof is pulled over PARKEN in Copenhagen. If there are 40,000 spectators inside the closed stadium they produce approx. four tons of water vapour per hour. If there is a low temperature outside the stadium the textile roof may be so cold that the water vapour is condensing and rain will fall on the spectators. This problem is solved by designing a roof made of two layers of textiles which are ventilated, and by using a powerful ventilation in the spectators' area. The ventilation nozzles in this area can also be used for heating of the whole concrete structure immediately after PARKEN is covered by the movable roof.