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Knockdown rebuild or modular — what changes when there's a house already there

From Modular Living Australia — the independent knowledge base Last updated: 8 Oct 2026

Before a knockdown rebuild, whether the new home is modular or not, the old house has to be checked for asbestos: a home built or renovated before 1990 may contain it, and only laboratory testing by a NATA-accredited lab can confirm it.^[1][2] More than 10 m² of non-friable asbestos needs a licensed removalist and friable asbestos a Class A licence holder; in Queensland asbestos must be removed before demolition so far as reasonably practicable, and a demolition licence or council approval may also be required.^[1][3]

Almost every comparison on this site starts from an empty block. A knockdown rebuild does not. There is a house on the land, someone is probably living in it, and before any new construction can begin the old building has to be assessed, stripped, approved for demolition, demolished and carted away — with the site's services disconnected somewhere in the middle.

Those steps sit in front of the build regardless of how the new home is constructed. What changes between a conventional rebuild and a factory-built one is where they sit in the sequence, and that turns out to matter more than most people expect.

The three layers a rebuild adds §

A rebuild is not just "a new home plus demolition". It adds three distinct workstreams that a greenfield project does not have: hazardous material assessment and removal, demolition approval and licensing, and disconnection of existing services. Each has its own approvals, its own licensed trades and its own lead time, and none of them can start after the new build starts.

Asbestos — the age of the house decides §

If a home was built or renovated before 1990 it might contain asbestos. Asbestos was used in a wide range of building materials before being phased out by 1990 and banned in 2003, and it remains present in millions of Australian homes and public and commercial buildings.^[1]

You cannot tell by looking. Only scientific testing of a sample can confirm whether a material contains asbestos, the sample must be tested by a laboratory approved by the National Association of Testing Authorities, and the sample should be collected by a competent person — an occupational hygienist, a licensed asbestos removalist or a NATA-accredited laboratory. Where material is known or suspected to have been installed before 1990, the safest approach is to assume it contains asbestos.^[2]

The regulatory picture then splits by jurisdiction and by asbestos type:

Ten square metres is less than it sounds. It is roughly four sheets of asbestos cement wall sheeting, or one wall of an average-size bathroom.^[1] A mid-century fibro house is not a marginal case.

Demolition is its own approval §

Construction work requirements in the Work Health and Safety Regulation 2011 apply to demolition work generally. Where the structure contains asbestos, sections 452 and 453 require the asbestos to be removed before demolition commences so far as reasonably practicable — and if it is not removed, the duty holder must provide evidence as to why removal was not reasonably practicable. Where removal beforehand is not reasonably practicable, methods such as wet spray must be used to minimise airborne fibres during the demolition.^[3]

Two separate approvals can be in play. The person performing the demolition may require a demolition licence issued under the Regulation, and specific demolition approval may also be required from the local council.^[3]

For planning purposes, the relevant point is that this is a sequenced dependency: the hazardous material assessment feeds the removal, the removal precedes the demolition, and the demolition precedes anything you do with the vacant site. None of it compresses.

Where the construction method actually changes the outcome §

Here is the part that distinguishes a modular rebuild from a conventional one, and it is not about price.

In a conventional rebuild, the site is the factory. Demolition finishes, the block sits empty, and construction begins from that point — so the whole build duration is added to the demolition duration, and you are paying for accommodation somewhere else for all of it.

In a modular rebuild, the dwelling is manufactured off site while the demolition, asbestos removal and site preparation happen on the block. The two workstreams run in parallel rather than in series. That is the strongest structural argument for off-site construction on a knockdown rebuild, and it is a timeline argument rather than a cost-per-square-metre one. Whether it materialises depends entirely on whether your approval is in hand early enough for the factory to start — see how long does a modular home take to build and progress payments and off-site construction.

There is a financing consequence too. Overlapping the factory build with demolition means paying for factory progress on a site that currently has no house on it and soon has nothing at all. Lenders treat that differently from staged on-site construction, which is the core issue in can you get a mortgage on a modular home.

Where modular is the wrong answer for a rebuild §

Established suburbs are where knockdown rebuilds happen, and established suburbs are where modules are hardest to deliver. A narrow street, overhead power lines, mature street trees, a tight setback or no crane standing position can rule out volumetric delivery on a block that would suit a conventional builder perfectly well. The constraint is access, and it is assessed by looking at the street, not the plan. See delivery, transport and craneage.

Where volumetric access fails, panelised (flat-pack) construction sometimes still works, because the components arrive flat on a standard truck and are assembled in place.

An older house also usually means older services. Existing water, sewer, power and stormwater connections may be in the wrong position, at the wrong capacity or on the wrong side of the block for a new dwelling footprint, and an easement that the old house was built around does not disappear with the old house. See building over a sewer or easement and connecting water, power and wastewater.

The questions worth asking before you commit §

• Has a hazardous materials assessment been done, by whom, and is the laboratory NATA-accredited?^[2]
• Who holds the demolition licence and the asbestos removal licence, and which class?^[1][3]
• Is council demolition approval separate from the development approval for the new dwelling, and who lodges it?^[3]
• Is demolition inside the builder's contract, or a separate contract you hold directly?
• Does the factory build start before, during or after demolition — and what happens to the schedule if the demolition is delayed?
• Who is responsible for service disconnection and reconnection, and are the disconnection costs in the quote?

What is not covered here §

This page does not give demolition costs, asbestos removal costs, or the cost difference between a rebuild and a new build on vacant land. Those figures vary by house size, material, jurisdiction, disposal distance and site access, and no independent Australian survey of them was compiled for this page. Published builder figures would be commercial guidance rather than survey data.

It does not set out the demolition approval process for each state and territory. The requirements described above are drawn from Queensland's work health and safety regulator and national asbestos guidance; other jurisdictions administer their own demolition licensing and council approval arrangements, and those are not covered by the sources here.

It does not cover asbestos disposal requirements, air monitoring, clearance certificates, or the rules for workplaces, which carry an asbestos register obligation that private homes do not. It does not cover heritage listings or demolition controls that restrict knocking a house down at all — a real constraint in older suburbs and one to check before any of this becomes relevant. And it does not cover the tax treatment of demolishing an income-producing property, which is a matter for a registered tax agent.

References §