Rooftop details

[Mr Fixit]

A question arose last year on a visit to NYC. Do any other cities have rooftop water towers? These are things that look like a N scale water tank on a O scale highrise.

The main purpose of the roof top water towers you are describing is to provide a water supply and improved water pressure.
In a lot of cases their use depends upon the age of the building and type of construction. The type you are referring to would have been either built or retro fitted to older solid brick or lower steel framed buildings built prior to WW11 as a rough guide.

All multi-storey buildings constructed today have one or more plant rooms occupying part or full floors as well as roof top areas, depending upon total height and design. Really tall multi storey 'sky scrapers' will have several plant rooms spread out over the height of the building and occupying full or part floors. Its one way of getting rid of the 'unlucky' 13th floor. While they may contain water tanks for drinking water, service uses, air conditioner use and fire service supply, they are not as visible as the roof top water towers you are talking about. Roof top plant rooms today tend to be located in fully enclosed plant rooms or screened plant rooms open to the sky. A lot of the space in a plant room is devoted to air conditioning requirements as well as electrical, data/telecommunications, and computing/server rooms. Moving air at the 'right temperature' takes up a lot of energy as well as space vertically and horizontally within a building. The 'smarter' a building is today, the more heat that is generated by the equipment and the greater the electrical power requirements.

One way to think of an occupied building is like a human body, with similar requirements for air and water to be supplied and then disposed of and power to 'do things' and to be able to communicate.

I hope that this has helped with your understanding of roof top details.

Mark