When Do I Need a Retaining Wall?
Why and how to make use of retaining walls on your property.
A retaining wall has one primary purpose: to retain. To put it simply, retaining in this context means supporting soil laterally so that it can be kept at two different levels on either side. Such walls can be made out of wood, brick, stone, and just about anything else you’d make a wall from, and they are very useful in landscaping to differentiate and level various parts of a lawn or garden.
Are retaining walls a want or a need? The answer is a mixed one: Often, they are necessary in order to achieve things that you may want to do with your property. Read on to find out when a retaining wall should be used and how to go about it.
Angle of repose
The “angle of repose” of the soil in the area you are working with is the major consideration for whether a retaining wall will be required. This refers to the natural slope of the spoil, which will depend on the type of soil in question, and whether there is vegetation holding it in place. If you would like to make changes that will create a steeper slope than what is naturally occurring—i.e flattening out a section of lawn which in turn means that another section has less space in which to fall—then a retaining wall is needed.
A good retaining wall will hold soil back against its tendency to move downhill and achieve its natural angle of repose. The more soil being held back, the stronger the wall will need to be!
Why build a wall?
There are many reasons a property owner might want to change the natural angle of repose of their land. It can create flatter surfaces on either side of the wall, which is fantastic for lawns, patios, and more stable vegetable or flower gardens. Retaining walls can be used to keep soil back from driveways or away from walls and basements to reduce dampness. They can also create walkable pathways.
Retaining walls can also prevent soil erosion. When land is flattened above or below the retaining wall (or on both sides), runoff is reduced. This means less soil is eroded.
Rules and recommendations for retaining walls
Once you have determined that a retaining wall must be built, the legalities are the next matter of concern. Additionally, if you are undertaking a large project it may pay to consult with an engineer to ensure your plans can be fulfilled safely. You should also check the title document for your property to discover whether there are any restrictions surrounding earthworks—particularly if your property is steeply sloped or near a natural feature like a river or cliff. If you are planning to build your wall from wood, a very common material for retaining walls on residential properties, you should ensure good drainage so that water does not sit in the soil being retained and cause the structure to rot.
Generally, building consent is not required for retaining walls which retain less than one and a half metres (in depth) of ground, if it is not also supporting any additional load. For example, if the retained soil will support a driveway or the ground slopes steeply above the retaining wall, consent is required. If the fall is more than one metre, a safety barrier should also be constructed.
Retaining walls are an extremely useful tool in any landscaper’s arsenal. To be effective in their goals, they should be constructed well—and this is especially important for any wall that is sizeable or supports a significant load of soil. If you’d like help to get your retaining right, contact the Maintain Your Property team. We are experienced in planning, constructing, and maintaining strong and effective retaining walls, and would love to chat with Wellington property owners about this and any other maintenance services for commercial and residential properties.