Council counts digging for underpinning as building work, and 1 vertical metre is a line in its rules

Two approvals, two decision-makers

Council's filling and excavation guideline separates two kinds of permit. Development that is assessable under the City Plan is typically assessed by Council, which the guideline calls the assessment manager for it. Assessment that is required under the Building Act is managed by building certifiers instead. The guideline adds that some development can be subject to more than one type of assessment and need multiple development permits.

Digging for underpinning sits on the building side of that division. The guideline says filling or excavation is classified as building work when it is directly related to, or incidental to, underpinning a building, and it lists underpinning works below an existing building among its examples.

Where 1 vertical metre comes in

Council's page on filling and excavation sets its line in terms of ground level. A project that aims to increase the depth and height of the ground level by up to 1 vertical metre does not need planning approval, unless the site is in a neighbourhood plan area affected by an overlay. Building approval is needed if the work involves filling or excavating more than 1 vertical metre of land to construct a building or structure.

Whether a dig under an existing house counts as constructing a building or structure for that last sentence is not something the page says. The same page warns that some neighbourhood plans and overlays change how much filling or excavation can happen without planning approval, and the pages for the seven suburbs on this site each say what the public map shows there.

Why the certifier belongs in the quote

The page tells a homeowner to contact a licensed building certifier to organise building approval. The guideline says the work of identifying the type of development and the level of assessment is usually dealt with by private building certifiers, and it recommends that a certifier or planning consultant is engaged for requests like these.

For someone comparing quotes, that becomes two questions the quote should answer: who engages the certifier and whether that cost sits inside the price, and what happens to the price if the certifier decides approval is needed after the quote was given. This site does not set prices and does not do the work; the provider an enquiry goes to answers them.

What neither document says

Neither the Council page nor the guideline gives a fee for a building certifier or a time for building approval, so this article cannot give either. They also leave open which side of the 1 vertical metre line a small dig under an existing house falls on. That is a question for a certifier who has looked at the site. The guideline does say that if filling and excavation works are minor, the work may be prescribed accepted development, meaning no development permit is required, and it does not define minor.