I don't know if they planned this when they designed The Sage building but cleaning the windows is tricky. So much so, they have devised a new method.
It is similar to bungee jumping except that on the ground there is a large vat of soapy water in which the cleaners 'dip'. On the way back up they splash themselves all over the windows, like human sponges. Someone on the ground then positions a vat of clean water for them to rinse the soap off the building.
They call the new method 'Spongy-jumping' or 'Spongebobbing'.