What is Subsoil Drainage?

A subsoil drain is a drainage system that is used to remove excess water from the ground or soil around a building.

If you have a section of land that gets heavily saturated or flooded when it rains, subsoil drainage can help move the excess water and increase water flow so that surface water can properly drain through.

Most homes already have some sort of drainage system in place, yet older homes may not have sufficient drainage. If they have earthenware field tiles, these may be damaged from age and years of ground movement.

Homes built on an uneven landscape that has varying contours or levels may also need additional subsoil drainage.

A subsoil drain is also sometimes referred to as a French drain. This name, however, drain does not come from France. The term French drain comes from a man named Henry French. He was a farmer in Massachusetts, USA who promoted the technique in an 1859 book about farm drainage.

What is the Purpose of Subsoil Drainage?

Subsoil drainage is used for a variety of purposes. The most common ones are:

  1. Subsoil drainage is used to clear or drain boggy lawns – a problem often seen in land sections prone to flooding or where there isn’t sufficient natural drainage or run-off.
  2. Subsoil drainage is useful to help prevent water damage to a property. If you notice mould or discolouration around the base of your property or the pilling, or there is stagnating water that isn’t draining away properly, then you probably need to install subsoil drainage.
  3. Subsoil drainage is always needed around retaining walls. If you are having a retaining wall erected on your property, it’s essential to have adequate drainage to ensure the integrity of the retaining wall.

What are the Benefits of a Subsoil Drain?

Using subsoil drainage to control water and run-off around your property brings a number of benefits:

  • Subsoil drainage helps to minimise or reduce structural damage to your property
  • Ground stability is enhanced, minimising the likelihood of damage to your building foundations or pilling
  • Retaining walls and landscaping withstand the effects of weather and last longer
  • Excess water entering the landscape and/or building is greatly decreased
  • Subsoil drainage can help reduce the salinity (salt content) of your soil
  • The soil is better aerated and is healthier for your plants and grass
  • By creating better drainage, a subsoil drain can help improve the quality of your fruit, vegetables, flowers and plants

How Does a Subsoil Drain Design Look?

There are a few different types of subsoil drainage. The most common one consists of slotted or perforated pipes. These are covered by a geotextile material which prevents soil and debris from getting into the pipes. This is then placed in the ground around the base of a building or wherever there is insufficient drainage.

There are other types of subsoil drainage, including:

  • Subsurface pipes
  • Interceptor drains
  • Mole drainage
  • Groundwater pumps

The qualified team at Sumich Plumbing & Drainage can determine which type of subsoil drainage is best suited for your land and property.

How To Install Subsoil Drainage?

It’s important to have an experienced certified drainlayer install subsoil drainage for you. We are well-informed about the regulations regarding where and how subsoil drainage can be discharged.

For example, subsoil drainage must discharge into a cesspit or holding pit to clean out any debris before overflowing into an approved point of discharge. This can include:

  • Existing stormwater system
  • Pumped chamber
  • Curb discharge
  • Soak holes

When we design and install a subsoil drainage system for you, we’ll look at factors such as the land area, average rainfall and the type of soil.

We also take into account whether the subsoil drainage system needs to work around a retaining wall, veggie garden, tennis court, swimming pool, or any other elements that may affect the efficiency of the drainage system.

Because subsoil drainage is vitally important for the structural components of your property and the natural elements of the land, we strongly advise using a professional drainlayer to install your subsoil drainage.


How Much Water Can Subsoil Drainage Handle?

The short answer is … as much as it needs to.

There is no one-size-fits-all approach when it comes to subsoil drainage. We will assess your property, the features of the ground and soil, the average rainfall in your area, the age and condition of your current drainage system, and any other factors that may affect your drainage.

This allows us to determine the drainage capacity that you need. We look at run-off in litres per minute, the size of the pipes and channels, and the size and shape of the discharge points.

Will a Subsoil Drain Prevent Water in a Basement?

Subsoil drainage is one of the best ways to prevent water from entering your basement, the lower levels of your home, and any storage space you have under your house.

We see subsoil drainage as a very effective form of drainage on sections where a house sits on a slope and there is access to the space underneath the house.

Subsoil drainage improves drainage of rainwater from the ground so that it is not accumulating against the in-ground walls, pooling around the base of the property, or seeping into the foundations.

As more and more New Zealand homes are being built with basements, it’s important that you have proper subsoil drainage installed.

If you’re building a new home, renovating, or have any concerns at all about the water drainage from your property, give the friendly team at Sumich Plumbing & Drainage a call.

We can help determine which type of subsoil drainage is best suited for your land and property.