How to design a plumbing system

Written by ben wakeling | 13/05/2017
How to design a plumbing system
Plumbing systems are required to provide and remove water. (plumbing image by Inger Anne Hulbækdal from

When building your new home from scratch, or extending your existing house, you will need to design a plumbing system that will provide hot and cold water to all kitchens and bathrooms, as well as remove waste water safely and efficiently. Traditionally, copper pipes were used for plumbing systems, but today many supply pipes are made out of plastic or polybutylene, with drainage pipes often made out of white PVC.

Obtain a copy of your house plans, or make a drawing to scale of your existing home if you are making renovations.

Before working out the position of items such as toilets, baths and showers, check your latest building code, as it may stipulate that they must be a certain distance apart. Ensure that your designs show both a hot and cold feed to the items that require it. Use this plan to work out where each plumbed appliance will be located, such as your dishwasher, sinks, toilets and washing machine.

Calculate each item's requirements for ventilation, which will allow for the removal of toxic gases caused by waste and sewage. The build-up of gases can transfer bacteria and alter the air pressure in the pipes, resulting in a problematic system. Again, consult your local building code for requirements regarding this. The size of the vent stack depends on the number of items you are installing, but it should not be less than 1 1/4-inch in diameter.

Mark out the waste drainage pipes on your design. This takes dirty water and other sanitary waste away from your property and empties it into the public drainage system. Ensure that the pipes intersect with your ventilation system.

Measure your finished drawing to determine the exact length of pipework you require, as well as additional fittings such as 90-degree elbows.


Take great care when designing a plumbing system, as it can be costly to alter once installed.

Tips and warnings

  • Take great care when designing a plumbing system, as it can be costly to alter once installed.

Things you need

  • Building code
  • House plan drawings

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