An extension site cut in Melbourne is not a greenfield pad with the fences taken down. You are digging beside a house that has to stay, often with a side path under a metre wide, and the engineer’s pier schedule does not leave much room for a bucket that wandered.
How an extension dig differs from a new build
A new house on an open block is a bulk cut and a line of trucks. An extension is a strip of ground beside a wall, under an eave, sometimes with a downpipe, a gas meter and a 900 mm side path. Machine size drops. On many Caroline Springs, Sunshine and inner-west renovations that means a 3–5 tonne mini excavator, not the machine we would use on a Melton estate lot.
The spoil has nowhere to sit. Every bucket has to move toward the street or into a truck staged out the front. That is why the hourly production looks poor if you compare it with a greenfield cut of the same cubic metres. You are paying for care and for double-handling, not for a lack of effort.
Read the tight access guide if the side gate is the constraint. The extension is the same problem with an existing footing you are not allowed to scar.
Piers, beams and the footing you must not undermine
Rear extensions often arrive as a beam line with bored piers, commonly on the order of 450 mm diameter at the spacing on the engineer’s sketch, not at a spacing we invent. We dig those holes to the depth and diameter on the plan and we stop if the hole collapses, hits water, or finds rock before the design toe.
The existing slab or strip footing is the hold point. Cutting “a bit wider so the machine fits” can undermine it. If the drawing is ambiguous about the offset, we ask before we continue. A phone call is cheaper than an engineer’s inspection of a footing you have just unloaded.
The longer explanation of collapse, water and rock in pier holes is on the bored pier page. Extension quotes should say whether pier holes are included or counted as an extra, because a “cut only” price that discovers twenty piers on the day is not a cut only.
A sequence that protects the house
A workable order is: protect surfaces and downpipes, strip what has to go, cut the extension footprint to the level, dig the pier or strip footing lines, let the plumber trench if that is in the same visit, then stop for the inspection the builder wants before any concrete. Rain on an open pier hole in reactive clay is a collapsed hole. Program the pour with that in mind.
Services already in the ground — stormwater from the existing house, a sewer branch, garden irrigation — are easy to break because they were laid for a yard, not for a machine. The locate and the plumber’s sketch matter as much as on a new build. See Dial Before You Dig notes for the habit, and still get the owner’s private pipes marked. Those do not show on every asset plan.
Heritage overlays and tight inner-suburban sites add steps that a Melton estate will not. We do not list council fees here. If your surveyor has a condition, send the condition. We follow that, not a generic suburban assumption.
Getting the clay out without wrecking the path
Spoil from a small extension is not a day’s worth of truck-and-dog. It is still clay that cannot stay on the lawn you mean to keep, or on the neighbour’s side path. Buckets, a mini tipper, or a larger truck at the kerb are all normal. The method belongs in the quote because it changes the hours.
Our soil removal and truck work pages cover ordinary cartage. On an extension, ask specifically where the truck stands and whether the council expects a permit for that standing. We will include it when we are pricing it. We will not assume the nature strip is a loading dock.
Rock and old concrete paths are the extras that blow a small budget. A buried path under the lawn is common. Price a rock and concrete allowance the same way as a full site cut that hits rock, scaled to the volume, not ignored because the job looks domestic.
What to send with the extension plans
The structural drawing, not just the floor plan. A photo down the side path with a tape in the frame. Overhead wires and the eave height if the machine has to pass under them. Where the spoil can go. Whether the existing floor level is the benchmark the new cut must hit.
Small rear extensions often land in a guide range of $2,500–$7,000 for the cut, pier holes and spoil away when access is ordinary and rock stays away. Double-storey rear builds with deeper strips sit higher. That range is from the work we see. It is not your price until we have the PDF.
Call 0414 011 405 or send the plans through the quote form. If the house is being demolished rather than extended, that is a different page — the full cut after a knockdown — and it should not be priced as an extension.
FAQ
Why do extension digs cost more per cubic metre?
Less room, a smaller machine, and spoil that often has to be carried to the street. The published guide range on small rear extensions is often $2,500–$7,000 for cut, pier holes and spoil away, with rock or a buried path on top. The range is a guide from jobs we see, not a quote for your plan.
How close can you dig to the existing footing?
As close as the structural drawings allow, and no closer. Undermining the existing footing to ‘make the bucket fit’ is the expensive mistake. We stop at hold points the builder or engineer has marked.
Do you need the building permit papers?
The earthworks usually sit under the building permit for the extension. Send the footing plan. If you are unsure what the council has already asked for, read the permit notes and ask your building surveyor rather than assuming a vacant-lot rule applies.
Can pier holes be in the same visit as the cut?
Yes when the schedule, the access and the spoil plan are in the one quote. Water, collapse and rock before design depth are the reasons a pier visit sometimes splits from the bulk cut. The pier note covers those stops.