Plumbing System Design for Multiple, Multi-Story Dwellings

Designing plumbing systems for multiple dwellings and multi-story housing units requires careful attention to factors that are substantially more complicated than those for single-story dwellings. The following overview of some of these important factors can help you understand the what needs to be considered when designing a plumbing system for multi-story dwellings.

Definitions

Multiple dwellings refer to structures that house more than one individual or family in separate units. These types of dwellings can be apartment buildings, hotels, military barracks buildings, tenements, boarding schools, nursing homes and other locations where multiple people live in relatively close proximity to each other. Multi-story dwellings are structures with more than one floor, but in the context of plumbing, a multi-story building is one that can’t be fully and adequately served by the municipal water supply because the pressure is too limited. Multi-story buildings also require drainage, sewage and venting systems that can accommodate many people living in a generally vertical arrangement.

Increasing Water Pressure for Multi-Story Buildings

In multi-story buildings, water pressure will often need to be increased to ensure that water is reaching the upper levels of the structure. This can be accomplished in several different ways:

• Installation of booster pumps: A series of staged pumps or variable-speed pumps can be installed to provide increased pressure for water drawn from the municipal water supply or from gravity storage tanks. These pumps supplement pressures from existing water supply sources.
• Using a gravity-based roof tank: Water is pumped from a ground-level or basement-level storage tank into a roof tank that attains adequate water pressures through gravity.
• Use of hydro-pneumatic storage tanks: Water is pumped from municipal supply lines or gravity storage tanks into hydro-pneumatic storage tanks that use internal air pressures to increase the water supply line pressure.

Avoidance of Cross-Contamination

Multi-occupancy, multi-story buildings must have plumbing system designs that prevent the possibility of cross-contamination of drinking water from one dwelling to another. Carelessness or unsanitary behavior from one resident or tenant should not affect the water quality of any other tenant. This is also true if the building houses commercial facilities, as well as residential units.

Installation of Control Valves

Multi-dwelling units should have control valves installed to control water supplies to each individual unit. This will help with preventing cross contamination. It will also ensure that water supplies to separate units can be shut off during maintenance or repairs without affecting the water supply to other dwellings. Control valves also give building managers and owners the option to stop water flow to unoccupied units. In cold weather, for example, this could reduce the chance of pipes freezing in vacant units.

Sewage and Waste Systems

Waste disposal, sewage systems and drainage must be designed to accommodate a larger and more consistent flow of greywater and human waste. These systems can be designed and implemented using multiple principles, including:

One-pipe systems, in which all solid waste and waste water from all units are directed to a single common pipe stack that carries material to the municipal waste system or other underground drains. All branches are ventilated to sustain proper air pressures. One-pipe systems are commonly used if there’s a risk of frost or freeze damage to the pipes, or where the building plumbing system is especially large and complex.

Two-pipe systems, in which solid waste and greywater are handled by separate pipe installations. Two-pipe systems are generally discharged into gullies or other geographical features.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection, and Alarm Systems in Mechanical, Commercial, and Residential settings. For more information on plumbing system design for multiple occupancy, multi-story dwellings, and to view projects we’ve worked on, visit our website!