In September 2000 the retractable membrane roof covering the court yard of the Vienna town hall was inaugurated. Giving shelter against rain and sun, the new structure with an area of 34 m ? 32 m replaces the former tents sheltering numerous events which take place here every summer. The transverse orientated steel-cables are anchored at carriages, which can be moved along tracks orientated perpendicularly to the cables. The membrane spans between the transverse ridge and valley cables, causing practically only warp stresses in the membrane. Thick walled tubes are used to weigh down the valley cables, resisting the small wind uplift forces in the courtyard and ensuring the accordion like folding process during retraction.