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High-rise plumbing: roof tanks, risers & pressure

Getting water to the 20th floor takes pumps, tanks and pressure zones. Here's how it works, and why pressure and leaks behave differently in tall buildings.

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01How water reaches the top floor

City water pressure in NYC typically reaches about six stories. Above that, buildings use a house pump and roof tank (gravity feeds the floors below), or booster pumps that keep the system pressurized. Very tall buildings divide floors into pressure zones with pressure-reducing valves, so lower floors don't get too much pressure.

Pump, roof tank, risers and stackDiagram D2
  • Cold water
  • Hot water
  • Drain / waste / sewer
  • Vent
Schematic of water supply and drainage in a ten-story New York apartment building City water enters the basement. A house pump lifts water through an up-feed pipe to a roof tank. Gravity then feeds a down-feed riser that branches to each floor, so pressure is lowest on the top floors closest to the tank. In some buildings, lower floors are fed directly by street pressure. A drain stack collects waste from every floor and runs down to the building sewer, with a vent through the roof. Configurations vary; some buildings use booster pumps instead of a tank. STREET 10987654321 BASEMENT roof tank house pump lowerpressure higherpressure 12345678
  1. 1City water enters at street pressure. In NYC that is typically enough to reach about six stories
  2. 2House pump lifts water from the basement
  3. 3Up-feed line to the roof tank
  4. 4Roof tank stores water; gravity creates the pressure below
  5. 5Down-feed riser: one shutoff often serves a whole vertical line of apartments
  6. 6In some buildings, lower floors are fed directly from street pressure (dashed)
  7. 7Drain stack: shared by every apartment stacked above
  8. 8Vent through the roof

02Roof tanks

NYC's wooden and steel roof tanks are a gravity system: pressure comes from the height of the tank, so the top floors get the least. Tanks need regular cleaning and inspection, and owners are responsible for their upkeep.

03Common high-rise problems

  • Low pressure on top floors, or too much on lower floors (failing pressure-reducing valves)
  • Leaks between floors from risers, valves or unit fixtures
  • Hot water swings from mixing valves or recirculation problems
  • Building-wide shutoffs because old riser valves don't close
  • Pump failures causing outages on upper floors

04For owners and boards

  • Replace seized riser valves so lines can be isolated
  • Keep pump and tank maintenance records
  • Schedule stack jetting where kitchen stacks clog
  • Gas piping in most multifamily buildings needs periodic inspection under NYC Local Law 152

05Frequently asked questions

Why is my top-floor pressure weak?

In tank buildings, gravity pressure is lowest just below the tank. Some buildings add booster pumps for top floors.

Do all high-rises have roof tanks?

No. Many use booster pump systems instead.

Sources & review

Last reviewed . General information, not legal or engineering advice. Rules change and individual buildings differ.

  1. CooperatorNews, Water pressure in high-rises
  2. NRDC, Rooftop water tank maintenance in NYC
  3. NYC Dept. of Buildings, Periodic Gas Piping Inspections

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