Stormwater drainage plan for new home builds

by | Mar 14, 2023 | Advice & inspiration, Building basics & regulations, Building tips

Australia is world-renowned for its sunny weather, but any local will tell you that when it rains here, it pours! How your property handles stormwater runoff will play a vital role in protecting your house, block of land and other property. It’s an essential part of the development process so today we’re talking all about stormwater plans for new home builds. A well-designed drainage system could solve many problems during the next rainy season, so it’s worth the effort.

Drainage for Stormwater has the following benefits:

  • Protects water quality
  • Reduces flooding risks
  • Prevent water damage to properties and the overall environment
  • Avoid soil erosion and water pooling on site
  • Protects beaches, rivers, lakes and other natural areas from contaminants.

What is the Australian standard for stormwater drainage systems?

Stormwater Drainage Approval will be based on the guidelines set out in the National Construction Code (NCC), the AS/NZS 3500.3, Australian Standards and your local council’s guidelines. There is a lot covered in these documents, and it’ll vary from area to area. However, we can discuss some of the terms in more depth.

AEP (Annual Exceedance Probability)

This is a term you may come across which refers to the likelihood of flooding or excessive rainfall. For example, with flooding, an AEP of 5% over a hundred-year period suggests a major flood would happen once every 20 years. Weather is unpredictable and these numbers aren’t lore, however, they do help determine the odds of your area flooding and the requirements your drainage will need to meet.

Drainage Pipe Size

The standard size for stormwater pipes is 9o mm, however, they’re also available in 100mm. This offers 20% more capacity but also demands a higher price. Is it worth it? Only if you have a higher-than-average water flow (for example, if you live on a large rural property). Getting too hung up on the size of the pipe can lead to negating that there are other important factors, like the angle of the pipe and the location of your drainage system.

Components of a Stormwater Drainage system

Almost every property, whether it’s a house, a warehouse or an entire office block, will require some sort of site drainage to deal with rainwater on site. Most components often found in drainage systems include:

  • Gutters
  • Hard surfaces
  • Soft Landscaping
  • Grated inlets
  • Rain gardens
  • Underground storage tanks
  • Above-ground storage basins

Who is responsible for drainage planning?

Property owners are responsible for maintaining gutters, pipes, downpipes, pits and any other components on their own land. Anything outside their property, or any easement, is the responsibility of the council or local government.

How does stormwater drainage work?

A stormwater drainage system is designed to collect stormwater runoff from your property. A system of pipes carefully designed and strategically installed around your compound to catch water from the roof and ground when it rains.

The three main goals of a drainage system are:

  • Slowing down water flow and buildup to reduce the odds of flooding and erosion problems.
  • Reduce costs of cleaning and unblocking stormwater drains.
  • Retain water for tanks and filtration systems.

Drainage should be designed to achieve the best result for not just your property, but neighbouring properties as well (flooding your neighbour’s property is a big no-no).

Why is the drainage for stormwater so important?

In nature, stormwater runoff is absorbed by plants, grass and soil. Manmade structures like roads, driveways, parking lots and walkways, however, are all hard surfaces that will gather water unless there is some sort of drainage option. Excess water build-up can cause an array of problems for the environment, people and buildings. Water build-up can gather a wide range of unpleasant things from debris, rubbish, oil and more. If this pollution gets into the river or anywhere that supplies drinking water, this is a problem. Enough water build-up leads to flooding, erosion and structural damage to buildings.

Stormwater drains are designed to help combat these issues. Obviously, in severe weather events, stormwater drains won’t be able to handle the heavy rain, but in most cases, it will make a huge difference.

Who designs stormwater drainage systems?

Stormwater drains should be designed by stormwater engineers or qualified stormwater drainage experts. Councils will usually require plans for stormwater drains with every new building, both commercial and residential. This is to ensure that new stormwater drains will meet all codes and regulations and can handle all your requirements.

Stormwater drain design considerations

When it comes to designing your perfect stormwater drainage system, you’ll need to take into account the following:

  • Size you require for your needs.
  • Topography of the land – this will outline the contours of the land and provide an idea of the property’s natural drainage.
  • Your system should try to conform to the land’s natural drainage patterns.
  • Product Material – various materials can be used to build stormwater drainage systems, each with different levels
  • Most council regulations will require you to minimise the number of discharge points
  • A stormwater system and a sewerage system are two completely different things. This should always be the case and you should never connect the two.

Our tips to help ensure your new home build is compliant with Australian stormwater drainage standards

  • Remember there will be changes coming into effect with the National Construction Code 2022.
  • Take a contour survey to help better understand your land.
  • Make sure your contractors have an idea of the history of flooding in your area.
  • Maintain upkeep once your drainage has been completed.

Talk with a building broker for more help

For further information on how we can help you with your next build, get in touch for a free consultation today. Whether you’re looking to find your perfect builder or need help during your building process. Get in touch with us today to have a chat about your next build.

Book your free, impartial consultation today!


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Building a Home

Knockdown Rebuild

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Building a Home

Knockdown Rebuild

Home designs

Advice & inspiration