Re: Cleaing Costs for Skyscapers?
At the ground floor, the pressure is at equilibrium, so people can come and go freely. Within a few floors or so, the differential is not significant enough, so windows there theoretically can be opened, though they usually remain closed for reasons of climate control. As you climb up, the building's interior is set up to limit air egress back down to the ground (the mostly likely candidates are the elevator shafts, stairwells in really tall buildings tend to be clustered, limited to so many floors at a time), allowing the air pressure to be maintainable despite the altitude.
PS. Don't take my word for it. Ask the MythBusters, who confirmed the Toronto skyscraper incident. The pressure differential at 1000ft is just over 1/2psi, but note the size of those skyscraper windows. 1/2psi times thousands of square inches equals quite a few pounds of ultimate force on those windows.