Partial Demolition for a Rear Extension: How It Works in Balwyn and Boroondara

Walk down almost any street in Balwyn, Canterbury, Kew or Camberwell and you will see the pattern. A California bungalow, an interwar brick home or an Edwardian weatherboard with its front intact, and behind it a modern two-storey extension where the old kitchen, laundry, sleepout and lean-to used to be. That is the Boroondara renovation, and every one of them starts with a partial demolition.

Partial demolition is a different job from knocking a house down. The whole point is what you keep, and the work is planned around protecting it. This article explains how it is done, what makes it more involved than a full demolition, and what drives the price.

What usually goes and what usually stays

In a typical Boroondara rear extension the front two or four rooms, the hallway, the facade and the front section of the roof are retained. Everything behind a nominated line is removed: the old kitchen and bathroom, the rear bedrooms or sunroom, any lean-to additions, the rear roof, the back verandah and often a garage or outbuilding in the way of the new footprint. Internal walls in the retained section are sometimes removed too, to open the old rooms into the new living space, and that internal strip-out is part of the same scope.

The demolition line is set by the architect on the drawings, and agreeing exactly which walls, floors and roof sections are staying is the first conversation on any partial job.

Why heritage overlays matter here

Boroondara has extensive heritage overlays, and Balwyn, Canterbury, Kew and Camberwell are full of them. A heritage overlay does not stop you extending, but it usually means the front of the house and its street presentation are the reason the overlay exists, and the planning permit for the extension will spell out what must be retained. In practice that reinforces the partial-demolition approach: the front is protected, the rear is where the change happens.

It also means the demolition must not touch anything the permit says stays. We check the endorsed plans and the permit conditions before we start, and if there is any ambiguity about a chimney, a side wall or a verandah, we ask before we cut. Our permits and heritage approvals service covers the paperwork side, including the demolition consent that sits alongside the planning permit.

Protecting the retained house

This is the part that separates a good partial demolition from a bad one. When the rear of a house is removed, the front section is suddenly exposed at the cut line. Roof framing that was tied into the rear roof needs temporary support. Walls that relied on the rear structure for bracing need propping. Services that ran through the demolished section need to be isolated or rerouted so the retained rooms still have power, water and gas where the owner needs them.

Before demolition starts, the cut line is protected. The retained roof is weatherproofed with temporary flashing or a tarp system at the junction. Openings between the old and new sections are sealed against dust with plastic and temporary framing. Floors in the retained rooms are covered. Where the family is staying in the front of the house during the works, that sealing is the difference between a livable house and a miserable few months.

How the work is sequenced

Partial demolition is slower and more hand-driven than a full knockdown. The rear is typically stripped by hand first: fixtures, joinery, windows, doors, any salvageable timber or bricks. Then roofing and framing come down in a controlled order, working away from the retained section. Machines are used where there is room, but close to the cut line the work is done by hand with saws and bars so nothing pulls on the structure that is staying.

Asbestos is a routine part of this in Boroondara, because the rear sections being demolished are so often the 1950s to 1970s additions: fibro sheeting in laundries, eaves, bathroom linings and the backs of lean-tos. It is identified before work starts and removed under the proper controls before the general demolition. Our asbestos-aware demolition and disposal page explains how that works.

Once the rear is down, the slab or stumps are removed if the new extension needs a fresh footing, the site is cleared and levelled to the builder's requirements, and the retained house is left sealed and safe for the builder to take over.

Working around neighbours on tight blocks

Boroondara blocks are often narrow with the house close to a side boundary, and the rear of the block may only be reachable down one side. That limits machine size and sometimes means material is barrowed or conveyed out. If the demolition is close to a neighbour's building or a shared fence, a protection work notice may be required under the Building Act, and the neighbour's property is protected accordingly. Tight-access demolition is normal for us across Balwyn North, Deepdene and Kew; it just needs planning.

What drives the cost

A partial demolition is priced on the work involved rather than the size of the house, and the things that push it up are the things that make it careful: the length of the cut line that needs propping and weatherproofing, the amount of hand demolition close to the retained section, asbestos in the rear section, access to the back of the block, internal strip-out in the retained rooms, and whether the old slab and footings need to come out. Salvage can offset a little of it if there are bricks or hardwood worth recovering.

Because so much of it depends on the specific house, we quote partial demolitions from a site visit and the drawings, not over the phone. What you receive is a fixed price for a defined scope, so there are no surprises when the builder arrives.

Fitting into the build program

The builder needs the site handed over in a known state, and the demolition scope should be written to match what the builder expects: what is retained, what is removed, whether the slab is out, whether services are capped and where. We align that directly with builders and architects across Boroondara.

If you are planning a rear extension in Balwyn or anywhere across Boroondara, the demolition is worth thinking about early, at the same time as the design. It will affect what can be retained, what the permit needs to say, and how the family lives through the build. Send us the drawings when you have them and we will walk the site with you.