Extensions are the most common work we draft, and the most consistently underestimated. On paper they look like a smaller version of a new house. In practice they're a different discipline, because you don't control the starting conditions — you inherit them.
Before a single line of the new work gets drawn, the existing building has to be measured and documented as it actually stands. Not as the original plans claim, and not as the owner remembers.
Houses get altered. Walls move, levels shift, a previous addition gets built off something that was never designed to carry it. Paper records — where they exist at all — are frequently wrong. We've lost count of the sets we've been handed where the recorded and actual dimensions differ by enough to matter.
Where the plans and the building disagree, the building wins. Drafting an addition onto assumed conditions is the most reliable way we know to manufacture site variations — and site variations are priced by the person holding the hammer, not by you.
A heritage overlay doesn't mean you can't extend. It usually means the street presentation is protected and the work happens behind it — a rear addition, set back, secondary in form, often deliberately contemporary rather than mock-period.
What it does mean is a planning permit, a heritage response, and a design conversation that starts with the constraint rather than discovering it. See town planning drawings for how that submission is assembled.
The most technically demanding version of this work. The existing structure has to carry a load it was never designed for, which means engineering early rather than late. Overlooking of neighbours becomes assessable. Overshadowing becomes assessable. And access — how material gets in, how the house stays weatherproof during the build — becomes a real constraint that ought to shape the documentation.
This is where a construction background earns its fee. We detail with sequence and access in mind, because we've done the version where nobody did.
Related: working drawings, residential building design, and projects we've delivered — including a California Bungalow reworked in Bentleigh.
Often not — many extensions are as-of-right and go straight to a building permit. What triggers a planning permit is the zone and any overlay on the land. A heritage overlay almost always does. So can a significant landscape or vegetation overlay, or building close to a boundary in some zones.
Check your address on the planning property report before you assume either way.
Because you inherit decisions. A new build starts from a level, empty site with known conditions. An extension has to connect to footings you can't see, floor levels that aren't level, walls that aren't straight, and a roof that was framed to a logic nobody wrote down.
Good documentation doesn't remove that cost, but it moves the discovery from the site to the drawing board, where it is far cheaper.
Yes, and it is not optional. We measure and draw the existing building as it actually is, not as the original plans claim. Old houses have been altered, and paper records are frequently wrong.
Drafting an addition onto an assumed set of existing conditions is the single most reliable way to generate site variations.
We can use them as a reference, and we can redraw a paper or scanned set into CAD. But we verify against the building. Where the plans and the building disagree, the building wins.
Each stage answers a different question, for a different assessor.
The construction set your builder prices and builds from.
View service → — DraftingThe set council assesses against the planning scheme and ResCode.
View service → — DraftingDocumentation your building surveyor assesses against the NCC.
View service → — DraftingMulti-dwelling work where Clause 55 decides the yield.
View service → — DraftingFabrication drawings — detailed in-house, not outsourced.
View service → — OverviewThe full picture: permits, drawing sets, consultants, timeframes and fees.
Back to drafting →Site address, sketch, brief, or just a question — we'll respond within one business day.