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How to: Retaining walls
In this second instalment of our focus on retaining walls, Nick Liefting explains the conditions under which Retaining Walls are exempt from building consent.
Consent for retaining walls
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Retaining walls that do not require a building consent under the Building Act 2004 are as follows:
Retaining walls up to 1.5 metres depth of ground:
The Building Act 2004, Schedule 1, Exemption 20 allows you to build a retaining wall (which is any wall constructed to retain or support the surrounding ground) without needing to get a building consent as long as it does not retain more than 1.5 metres (vertically) of ground and it includes ground water drainage in relation to retaining walls.
This exemption does not apply to retaining walls that are subject to any additional load or surcharge such as:
• vehicle driveways • parking spaces • swimming pools • buildings • other retaining walls • sloping ground above the top of the retaining wall If the ground above the top of the retaining wall is only gently sloping, this may not be considered as ‘surcharge’. To determine the impact of the sloping ground and its pressure on the stability of the proposed retaining wall, you may wish to seek professional advice, for example, from a Chartered Professional Engineer. Examples:
What is exempt?
1. A builder plans to reconstruct an earthquake-damaged timber retaining wall that is less than 1.5 metres high.
There is no surcharge on the retaining wall, so a consent is not needed. 2. A motel owner decides to terrace the motel’s uphill sloping section by building three, 1.2 metre high concrete crib retaining walls to create three level platforms, each of which will be planted. As there will be sufficient horizontal separation between each of the retaining walls so that no surcharge load will be imposed on a lower wall, no building consent will be needed.
What needs consent?
1. An owner wishes to form a level platform for a garden below a neighbour’s driveway. To do this, she intends to construct a 1.2 metre high retaining wall.
As the proposed retaining wall is subject to a surcharge from the neighbour’s vehicle driveway, it will require a building consent.
2. A retaining wall ranges in height from 900 millimetres to 1.8 metres. The part of the retaining wall that exceeds the maximum allowable height of 1.5 metres will require a building consent.
3. Retaining walls with surcharge regardless of height.
Retaining walls up to 3 metres depth of ground
The Building Act 2004, Schedule 1, Exemption 41 exempts retaining walls designed or reviewed by a Chartered Professional Engineer of up to 3 metres and in a rural zone, as long as they are not too close from the boundary or existing buildings. This exemption recognises that in low density rural zones such as farms, the consequences of failure of any retaining wall are less likely to cause injury than they would be in higher density urban environments. The additional requirement for a Chartered Professional Engineer to be involved also helps to make sure that retaining walls covered under this exemption are less likely to fail.
Examples:
What is exempt?
1. Constructing a retaining wall on a rural property that is 2.5 metres high, 3 metres away from an existing dwelling, and is designed by a Chartered
Professional Engineer. 2. A farmer decides to rebuild an earthquake-damaged retaining wall on their rural property that is 3 metres high and located 6 metres away from a legal boundary. The wall design has been reviewed by a Chartered
Professional Engineer.
What needs consent?
1. Constructing a retaining wall on a rural property with a height of 3 metres, 1 metre away from an existing dwelling and designed by a Chartered
Professional Engineer. A building consent is required because the wall is closer to the dwelling than its own height. 2. Constructing a retaining wall on a rural property that is 3 metres high and 5 metres away from the property boundary which has been designed by an engineer, but not a Chartered
Professional Engineer. Though the retaining wall is not located closer to a legal boundary than its own height, a building consent is required as the wall has not been designed or reviewed by a Chartered Professional
Engineer.
Article provided by:
Nick Liefting Nick Liefting Contractors Ltd nlcontractors.co.nz
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