How Extension Digs Differ From New Builds
New house: open block, bulk cut, trucks in and out. Extension: protect the existing slab, hand-dig near stormwater, maybe pier holes at 450 mm diameter every 1.2 m along the new beam line. Machine size drops to 3–5 tonne mini excavators on Caroline Springs and Sunshine renovations where the side path is tight.
What Extension Earthworks Cost in 2026
Small rear extensions often land $2,500–$7,000 for cut, pier holes and spoil away — less volume than a full house pad, but slower work per cubic metre. Double-storey rear builds with deep strip footings sit higher. Rock, asbestos sheeting buried in old fill, or cutting through an old concrete path adds lines to the quote.
Build Sequence Matters
Typical order: strip topsoil → cut extension footprint → pier holes → plumber trenches → inspection → pour. If you cut too wide and undermine the existing footing, you've created an engineer's nightmare. We work from the structural drawings and stop for hold points when the builder asks.
On extensions, the expensive mistake is gouging too close to the existing footing — slow and careful beats fast and wrong.
Permits for Renovation Earthworks
Still usually under the building permit for the extension. Same rule as new builds — see our Melbourne permit notes if you're unsure. Heritage overlays in inner suburbs add steps; greenfield Melton/Wyndham jobs rarely do.
Quote Checklist for Your Extension
- Structural / footing plan PDF
- Side access width and overhead height
- Where spoil can go (usually off site)
- Whether pier holes are counted separately or bundled