Partial vs full demolition: the honest decision guide

Not every demolition job is a bare block. A big share of our regional work is partial: removing a lean-to, a fire-damaged wing, a dodgy 1980s extension, or the back half of a house ahead of a renovation. Here's how the partial-vs-full decision actually works — including the cases where partial is false economy.

When partial demolition makes sense

• Renovations and extensions: removing the back rooms so a builder can extend. The most common partial job — typically $4,000–$12,000 depending on size and asbestos.
• Failed additions: sunrooms, sleep-outs and lean-tos that were never built well. Often cheap to remove and transformative for the block.
• Fire, flood or storm damage confined to one section, where insurance is funding reinstatement of that section only.
• Outbuildings: garages, sheds, dairies, bungalows — see the shed and garage guide.

What makes partial genuinely harder than full

Counter-intuitively, partial demolition is more skilled work per square metre than full demolition. The machine can't just eat the building — the cut line has to be surgical:

• Structural separation: the retained section must stay supported while shared walls, roof structure and footings are cut. That's saw and hand work, not grab work.
• Weatherproofing the cut: the exposed edge needs temporary or permanent sealing so the house you kept doesn't take water.
• Services: power, water and sewer runs usually pass through the section coming down, and must be re-routed live rather than abolished.
• Asbestos still applies: a 1960s lean-to is exactly where the fibro is. Same licensing, same process, smaller area.

This is why partial jobs price at a higher rate per square metre — and why the cheapest quote on a partial job, from someone who plans to treat it like a small full demolition, is the one that damages the house you're keeping.

Permits: yes, still

Partial demolition still needs a building permit, and Section 29A consent applies if you're taking more than half the building's volume (counted cumulatively over three years) or touching any street-facing facade. Renovators are caught by the facade rule more often than anyone expects — a front verandah counts.

When partial is false economy

• The keep-half is as bad as the go-half. If the retained section needs restumping, rewiring and reroofing, run the numbers on a knock-down-rebuild honestly — see the KDR guide. Renovating around a tired half-house is how $300k renovations happen on $450k houses.
• Staged demolitions. Taking the house down in two hired stages a year apart pays mobilisation, permits and asbestos setup twice. If the end state is a clear block, one job is almost always cheaper.
• "We'll keep the slab." Old slabs rarely match new designs, and builders routinely refuse to build on them. Keeping a slab to save $3,000 and losing it later costs more.

Protecting what stays

The retained house deserves the same care as a neighbour's property: dust sheeting over the cut, floors protected where trades pass through, a dilapidation photo record of the keep-side before work starts, and services confirmed live and safe at handover. Agree in the quote who patches the cut line to lock-up standard — leaving a renovation-ready open edge is fine if the builder is starting Monday, and a disaster if the builder is starting in spring.

A worked example: the rear-section removal

A typical renovation-enabling partial in our towns — removing a 45 sqm 1970s rear extension (fibro-lined, on stumps) from a weatherboard house ahead of a new build-out — itemises roughly: asbestos survey and licensed removal of the fibro lining $1,800; building permit and consents $1,100; structural separation, propping and cut-line weatherproofing $1,600; demolition, load-out and tipping $3,200; service re-routing by electrician and plumber $900; stump removal and rough grade of the cleared footprint $700 — about $9,300. The same floor area inside a full demolition would cost roughly half that — the premium buys the surgery that keeps your front half dry and standing.

The test an honest contractor applies

What's the end state, and what's the cheapest safe path to it? If that's a partial, we quote a partial, with the cut line, weatherproofing and re-routing itemised. If the numbers say the whole house should go, we'll show you why. Describe the job and we'll give you the straight version.