How to Design a Plumbing System for a Building

As a homeowner, the choices you make when planning home improvement projects such as toilet upgrades or installing new bathrooms also affect plumbing design. An efficient plumbing system begins with a design that focuses on water and energy saving. In this guide, we highlight tips on how to design a plumbing system for a building.

Whether you’re doing a DIY plumbing project or working with a licensed plumber, ensure that any designs incorporated in your remodel project use short runs between various plumbing fixtures as well as state-of-the-art elements that are ecofriendly. 

Typically, a plumbing design is made up of two systems: one that supplies clean water and another that gets rid of wastewater. The drain system will comprise of vent stacks to allow drainpipes to breathe and efficiently move sewer waste through sewer pipes.

Factors to Consider When Designing a Plumbing System

Here are the factors to consider when designing a new plumbing system for a bathroom, kitchen, laundry, and other rooms that require plumbing networks:

Plumbing Codes

Typically, plumbing installation and design must adhere to the local building codes to ensure legal and safety compliance. Plumbing codes limit the number of plumbing fixtures that can be installed on a vent stack or drain system. The number of supply lines and drains that must be placed inside walls is also limited. You can check with your local building jurisdictions to get the information about the applicable codes as well as situations when they can divulge from the standard codes.

House Design

Water supply to a building is one complete system that transverses various rooms. Both the clean water supply system and the DWV (drain, waste, and vent) systems are often designed to run alongside each other to save on materials and enhance water efficiency. So, if you’re working on any home improvement project, consider grouping rooms that require plumbing fixtures close together. For example, a new bathroom should be installed adjacent to a bedroom while a laundry area should neighbor a kitchen.

Water Supply, Hot Water System and DWV

Water supply and DWV (drain, waste, and vent) systems should sit side by side inside the walls of your house. This design strategy helps to save on water and energy consumption. Ensure that your hot-water plumbing loop system continually moves hot water back to your water heater. This significantly reduces the amount of energy expended in water heating. You could also opt for a solar hot water system or a point-of-use tankless hot water unit.

Materials and Building Contractors

Opting for cheaper materials and inexperienced plumbers will likely cost you more in the end. To get the most out of your plumbing design, ensure that you only purchase the highest quality materials and hire a highly-rated contractor who comes with good recommendations. A poorly fitted joint or incorrectly sloped drain system can cost you lots of money to correct later on.

Plumbing Design Parameters

Plumbing design encompasses several parameters. Generally, the water supply system must be designed to deliver appropriate water pressure and flow. More importantly, the design should ensure that clean potable water is not contaminated by greywater from the DWV system.

A good plumbing system must also be suitable for the various temperatures (hot or cold) of the water carried. A well-designed and installed plumbing system should also be durable, minimize noise from water flow, and ensure water efficiency.

Generally, water supply systems consist of a combination of pipes, valves, and outlets. Some systems may also include storage tanks and pumps, and you must get all these parameters right to ensure that clean water is delivered at the appropriate rate and temperature and wastewater is eliminated safely, and seamlessly.

In this section, we shall cover the following plumbing design parameters:

  • Water pressure
  • Water flow rate
  • System layout
  • Mains Connection
  • Pipe materials and specifications
  • Flow rate and acceptable pipe size
  • Backflow

1-     Water pressure

If your aim is to enable building occupants to use water efficiently, then the right water pressure is important. Too low water pressure will inconvenience building owners. For example, bathtubs will take too long to fill while shower heads will have poor water flow. Too high pressure, on the other hand, will lead to excessive water use, not to mention high wear on the plumbing system.

Typically, a building in areas with mains water supply has high water pressures. If the building is not connected to a mains water system, it may exhibit low water pressure or unequal pressure systems – that means different pressure levels for cold and hot water supply.

Mains pressure systems will require pressure-reducing and pressure-limiting valves to control water pressure and temperature. This is especially critical for mains-supplied hot water systems or in cases where high pressure can burst pipes.

On the contrary, low-pressure systems require fewer valves or controls. In such systems, pressure can be improved a bit by storing water in overhead tanks (usually in the ceiling space), allowing gravity to create water pressure. Water pressure can also be increased to sufficient levels by using a pressurizing pump. In such scenarios, it may be necessary to use pressure reducing and pressure limiting valves.

2-     Water Flow Rate

The Building Code requires that all sanitary fixtures and appliances receive adequate water supply at the right flow rate. As with water pressure, if the flow rate is too high, it will result in water being wasted. Too low flow rate, on the other hand, will mean that sanitary fixtures and appliances don’t function properly. In other words, your toilet bowls may take longer to fill, and uplush toilets may even fail to flush.

Flow rate is typically affected by:

  • Water pressure – The higher the pressure, the better the flow rate
  • Pipe diameters – The narrower the internal diameter of the pipe, the lower the flow rate
  • Water temperature – Higher temperatures tend to raise water pressure and flow rates

You can use a flow regulator to maintain constant water flow, independent of water pressure. For example, if someone is showering while the kitchen faucet is on, the flow and temperature levels will likely remain constant if a flow regulator is installed.

3-     System Layout

During the design, the layout of the plumbing system will to a large extent follow room layout. However, there are several factors to consider depending on code compliance, user comfort, and sustainability.

When planning a water supply layout, consider the following:

  • Pipe runs and lengths – Always keep pipe runs as short as possible by passing pipes close to fixtures to minimize the number of branches and unnecessary tees, elbows, and joints. Longer pipe runs and extra fixtures will increase heat loss, increase material use, and reduce flow rate.
  • Point of entry into the building – Choose an appropriate entry point in utility spaces such as laundry area or garage, and be sure to include an accessible isolation valve, pressure limiting valve, and a line strainer.
  • Water heating system – Install the water heating system centrally to reduce the length of pipe runs to various fixtures. For systems that are more than 10 meters away from the main water heater, consider installing separate point-of-use water heaters.
  • Noise prevention – Avoid laying pipes over or close to bedrooms and living areas.

4-     Mains connection

If the water supply comes from the mains supply, the utility operator is responsible for the flow rate and supply pressure to the property. The property owner will only take responsibility for the necessary pipework that brings water into the building. An isolating valve should be installed at the point of connection to allow easy maintenance and repair of water supply systems and plumbing fixtures as may be required.

5-     Pipe materials and specifications

The supply pipes used in a property must not contaminate the potable water supply. They must be suitable for the flow rate, water pressure, and temperature of the water they will be carrying. The material used as well as wall thickness will also affect the specifications of supply pipes.

Other considerations include durability, cost, ease of installation, and sustainability. The most common supply pipes for domestic properties include polybutylene (PB), copper, polyethylene (PE), cross-linked polyethylene (PEX), and polypropylene (PP-3 or PP Type 3).

Flow rate and Appropriate pipe size

The BOCA Plumbing Code (Borland Object Component Architecture) sets out the required flow rates and pipe sizes. All pipes must be properly sized to achieve the right flow rates in a plumbing system. Here are a few specifications in the code, but you can get the full details in this PDF:

  • Basin – 0.1 l/s at 45 °C
  • Bath – 0.3 l/s at 45°C
  • Sink – 0.2 l/s at 60°C (hot) and 0.2 l/s (cold)
  • Shower – 0.1 l/s at 42°C
  • Laundry tub – 0.2 l/s at 60°C (hot) and 0.2 l/s (cold)
  • Dishwasher and washing machine – 0.2 l/s


Backflow refers to the unplanned reversal of the flow of water (sometimes water and contaminants) back to the water supply system. The plumbing system must be designed to prevent water contamination from backflow.

Wrap Up

Ultimately, plumbing codes play a critical role in plumbing design and installation. These codes are not just arbitrary rules written to frustrate homeowners or contractors seeking to execute various home improvement projects. They are designed to ensure the safety of homeowners and improve water and energy efficiency in homes and commercial buildings. Be sure to follow and adhere to them in all plumbing designs and installations.

Smith Edwards

Smith Edwards is a licensed plumber and writer with over a decade of hands-on construction and home improvement experience and has been providing home improvement advice for over 12 years.

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