More and more Manhattan towers are being built on narrow pieces of land and as a result there is a little sway at the upper floors. According to NYT though, this is mitigated by installation of dampeners on the upper floors. Some dampeners add weight to the higher floors and some systems act as a shock absorbers. How much sway is there? The analogy used is having a wine glass and with high winds that are rare you can see the glass move. This would be what would happen without the dampeners. There isn’t a building code that requires this but all new development condos have them and it is not in anyway to make the building safe but rather for the comfort of the owners.