Extensions & additions
Rear, side and second storey additions across Sydney — structural work, not an addition bolted on. The difficulty sits in the footings, the roof junction and the drainage, and that is where the price sits too.
What it actually is
An extension is often described as extra space bolted onto a house. It is not. It is footings, a roof that has to meet an existing one, drainage that has to find a fall it did not need before, and a junction between old fabric and new. The difficulty and the cost sit in those four things — not in the square metres.
Licence 297590c · HIA member 1220336 · structural work · Sydney only
Three kinds
Which one a house can take is decided by the block, the existing structure and the planning pathway — usually in that order.
The most common, and usually the most worthwhile. Opens the back of the house to the garden and the northern light, and moves the living spaces to where the sun actually is rather than where the original plan put them.
Where the block allows width. Often the answer on a wide Federation block where going up would cost the roof line, and on corner sites where the setback is generous on one boundary.
Bedrooms, bathrooms and a retreat upstairs without leaving the street you chose. The roof comes off, so the house is exposed and staged weather-tight in sequence. Existing footings and wall structure are checked by an engineer before anything is priced.
The junction
Every extension has a seam. You can match the original and make the join invisible, or step away from it deliberately and let the new work read as new. Both are defensible. Pretending there is no seam is not.
Ridge and gutter levels rarely align — flashings are formed, not bought
A step between old and new is a decision, never an accident
Matched face brick weathers differently — sometimes contrast ages better
Existing gutters and downpipes may not carry the additional catchment
How it runs
One lead builder from first walkthrough to handover, inclusions and exclusions on paper before a tool comes off the truck, and a stated reporting cadence while it runs. The full sequence is set out on its own page.
Recent work
Rear and second storey additions across the Eastern Suburbs, North Shore, Northern Beaches and the Hills.
Questions
The planning questions come up on every extension. Short answers below — but the pathway is decided by your specific lot, so confirm it before you rely on it.
Almost always. The question is which pathway: a Development Application assessed by council on its merits, or a Complying Development Certificate issued under the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 — the Codes SEPP. Which one is available depends on the land, the zoning and the design.
A DA is a merit assessment by council, with neighbour notification, and takes as long as the assessment takes. A CDC is a combined planning and construction approval for work that meets every standard in the Codes SEPP — because it is a compliance check rather than a judgement, it can be determined by a council or a registered certifier in as little as 20 days. One variation from the standards and the project is back on the DA pathway.
Often not, in the suburbs we work in. Complying development is generally not available on land containing a heritage item or listed on the State Heritage Register, or on land within a heritage conservation area. It is also excluded on environmentally sensitive land, land affected by coastal erosion, and foreshore area within the foreshore building line. That covers a good deal of the Eastern Suburbs and parts of the Northern Beaches.
Four to eight months on site for most, depending on how much structure moves and whether the roof is opened up. Approvals sit in front of that and vary by pathway and by council.
Sometimes, for a rear extension where the existing house can be sealed off and the kitchen and one bathroom stay in service. For a second storey addition, usually not — the roof comes off. We tell you which it is at scope stage rather than after the contract is signed.
Often. A new storey adds load the existing footings were not designed to carry. Whether they need underpinning or supplementing is a structural engineer's call from a site inspection, and sometimes a soil test. Worth establishing early, because it changes both the program and the price.
Ridge and gutter levels rarely align, flashings have to be formed rather than bought off a shelf, and the existing gutters and downpipes may not carry the additional catchment. It is detailed at drawing stage. Extensions that look wrong from the street are almost always wrong at this junction.
Planning summary current at August 2026 · pathways and standards change, and vary by council and land zoning · confirm with your council or a registered certifier before relying on it
Start
Tell us what the house should become. We'll tell you honestly what it takes.
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