Knock Down Rebuild Finance: When the Old House Still Has a Mortgage
Self-employed and knocking down your home? How the existing mortgage, construction loan, approvals and One Doc take-out fit together.
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Knock Down Rebuild · Existing Mortgage · One Doc Take-Out
What happens to the mortgage when the house that secures it comes down, and how self-employed owners move from the existing loan to a construction loan and then a One Doc or low doc take-out.
Quick Answer
If you run your own business and want to knock down and rebuild your home, the existing mortgage is usually restructured into a construction loan secured on the land, then refinanced at completion into a home loan sized for the finished house. Self-employed borrowers can often use a One Doc home loan or low doc income evidence for that take-out, subject to lender policy.
Also called: knockdown rebuild loan, knock down and rebuild finance, demolish and rebuild loan. Same thing: a construction loan on land you already own, with an old house to clear first.
How do you finance a knock down rebuild when the old house still has a mortgage?
You finance a knock down rebuild by moving the existing home loan into a construction loan secured on your land, drawing that loan down in stages as the new home goes up, then refinancing into an ordinary home loan once the build is finished. That three-step crossover is the whole job. Most of the friction sits at the first step, because the house that secured the loan is about to disappear.
Some owners stay with their current lender and have the loan restructured into a construction facility. Others move to a new lender who pays out the old debt and folds it into the construction limit on day one. Either way, the old loan has to be dealt with before the excavator arrives, not after. The table below shows how the security and the payments shift at each stage.
| Stage | What the lender holds | What gets paid | Who to ask |
|---|---|---|---|
| Before demolition | The existing house and land, under your current home loan | Your normal repayments, while the existing loan is restructured or refinanced into a construction facility | Your broker and your current lender |
| Demolition and site work | The land only, now valued without a house on it | Demolition, asbestos removal and site preparation, where the lender funds them under the approved contract (lender policy decides) | Your builder, demolition contractor and certifier |
| Build stages | The land plus the partly built home | The builder's progress claims, paid as staged drawdowns once each stage is checked | Your builder and the lender's valuer or inspector |
| Practical completion | The land plus the finished home | The final claim, once practical completion is reached and the final certificate issues | Your builder and certifier |
| Take-out or refinance | The finished home, revalued | The construction loan converts or is refinanced into a standard home loan, often a One Doc or low doc loan for self-employed borrowers | Your broker and accountant |
For a self-employed owner, the first and last rows need the most preparation: the restructure before demolition and the income evidence for the take-out. The broader rules on building a home while self-employed sit in our self-employed construction loan guide. This insight stays on what is different when there is an old house, and an old mortgage, in the way.
What happens to your existing home loan when the house is demolished?
Your existing home loan has to be restructured before demolition, because no lender wants a loan secured on a house that will soon be rubble. Once the house comes down, land value carries the loan until the new home exists, and the loan to value ratio is measured against the land alone.
That is where some files stall. A loan that sat comfortably against a house and land can look stretched against land value only, especially in suburbs where the old house carried a large share of the value. Lenders typically want the existing debt to fit inside their limit for vacant land before they approve the construction facility, and that limit differs from lender to lender.
Where this commonly lands is a single construction facility with two parts: the existing debt rolled in at settlement of the new loan, and the build cost drawn as the home goes up. Interest on the rolled-in portion starts straight away; interest on the build portion grows with each drawdown.
What if the land alone does not cover the existing loan?
If the land alone does not cover the existing loan comfortably, the usual options are to pay the balance down before you start, offer another property as additional security, or contribute more cash to the build so the final loan is smaller. Demolishing before the restructure is settled is the one step to avoid: most mortgage terms require the lender's consent before the security is altered, and a lender that finds out after the fact has little reason to be flexible.
How is a knock down rebuild valued: the land now and the home at the end?
A knock down rebuild is valued twice: once on the land as it stands, and once as if the new home were already built. The lender sizes the construction loan against an as if complete valuation on land plus the new home (the method differs between valuers) and checks separately that the land value covers the debt in the early stages, before much of the house exists.
The valuer works from your plans, specifications and fixed-price building contract. A contract with vague allowances or a long list of provisional sums makes that job harder, and lenders usually want the contract to look like one they would accept on any build. Our guide to building contracts a lender will accept covers what they look for.
The valuation question that slows a knockdown rebuild most often is the gap between the build cost and what comparable finished homes in the street sell for. If the end value comes in under land plus contract price, the difference has to come from your own funds or the loan amount drops. The self-employed construction loan guide covers valuation shortfalls in general; the point here is that an expensive custom home on a modest street can value below cost. Your valuation is the number every later stage hangs from.
Can a One Doc or low doc loan fund a knock down rebuild for a self-employed borrower?
A One Doc or low doc loan can fund a knock down rebuild for a self-employed borrower, most often as the take-out loan at completion and, where a lender allows it, for the construction stage as well. Low doc construction lending is narrower than low doc lending on a finished home, and lenders typically hold it to a lower loan to value ratio, set by each lender's own policy.
A One Doc home loan assesses income on one primary document instead of full tax returns and financials. Depending on the lender, that can be BAS statements, business bank statements or an accountant letter confirming your income. For a rebuild, the same document usually has to carry two jobs: servicing the construction loan while you also pay rent, and supporting the take-out once the home is finished.
The cleaner path is often a full doc or alt doc construction facility, then a refinance to a One Doc home loan on the finished home. The take-out logic is the same as the one in our post on refinancing a finished owner-build with One Doc, and if business cash is tied up in the build, the One Doc mid-build capital post covers how lenders read it. Before you sign a building contract, check eligibility on the income evidence you actually have.
Which approvals have to be in place before demolition and the first drawdown?
Approval for the new home has to be in place before demolition and before a lender releases the first drawdown, and in most states the demolition needs its own approval or consent as well. The rules sit with your state and council, so treat the summary below as a map, not a checklist, and confirm the detail with your builder or certifier.
- New South Wales. The NSW Planning Portal's knockdown rebuild guidance is plain: no demolition until the new home is approved. Demolition itself is approved through a development application or a complying development certificate.
- Victoria. At the time of writing, a demolition permit needs a council report and consent where more than half the building's volume is demolished or the street facade is affected.
- Queensland. In Brisbane, building approval from a certifier is required before demolition. At the time of writing, Queensland requires a Class A licensed removalist for friable asbestos and at least a Class B licence to remove more than 10 square metres of non-friable asbestos.
Lenders generally fund demolition only when it sits inside the approved building contract or an approved quote, and only once the construction facility has settled. The usual order runs like this:
- Plans and contract. Final plans, specifications and a signed building contract.
- Approval for the new home. Development approval, a complying development certificate or a building permit, depending on the state.
- Demolition approval or consent. Through council or a certifier, with any asbestos survey the approval calls for.
- Construction loan settles. The existing loan is restructured or paid out and the facility is in place.
- Site cleared. Utilities disconnected, asbestos removed by a licensed contractor, house demolished, any council bond lodged.
- First drawdown. The builder's first progress claim, checked against the contract.
Where do you live, and who pays the rent, while you rebuild?
You live somewhere else while you rebuild, and rent sits outside the loan, so the lender assesses whether you can pay rent and construction loan interest at the same time. That double cost is the servicing test that catches more self-employed rebuilds than the valuation does.
Construction loans are usually interest only during the build, and the interest bill rises as each stage is drawn. Add rent, and your outgoings are at their highest in the last months of the build, which is also when delays are most likely. Lenders typically want to see income that covers both with room to spare, assessed on the same evidence they will use for the take-out.
A knockdown rebuild also carries costs that a build on vacant land does not. Check which of these sit inside your building contract and which you are paying yourself:
- Demolition and site clearing. Sometimes in the builder's contract, often a separate quote.
- Asbestos survey and removal. Common in older homes, and priced only after inspection.
- Utility disconnection and reconnection. Power, gas, water and sewer, each with its own provider.
- Temporary fencing, council bonds and storage. Small lines that add up across a long build.
- Rent and moving costs. Never inside the loan, always inside your servicing.
The general list of costs outside a building contract is in the self-employed construction loan guide, and our construction loan pack lists what a lender asks for before the facility settles. If you are thinking of running the build yourself to save money, the lending changes again; see our owner-builder construction loan guide first.
When does a knock down rebuild become a development?
A knock down rebuild becomes a development when you replace one home with two or more dwellings, and at that point the lending shifts from a home loan toward development finance. The lender starts asking what the finished dwellings are worth, whether any will be sold, and whether the project still looks like your home or like a business.
| Feature | Rebuild one home | Rebuild as two or more dwellings |
|---|---|---|
| Lending type | Residential construction loan | Moves toward development finance |
| Exit | Take-out to a One Doc or low doc home loan, subject to lender policy | Sale, refinance or both, tested on end values and any presales |
| Valuation | Land plus one finished home | Each finished dwelling; duplex valuations can fall short of cost |
| New-build tax treatment (2026-27 Budget) | Not a new build | Can count as a new build if supply increases |
A duplex on a knockdown block is the most common crossover. Our post on the duplex valuation gap covers why those valuations can disappoint, and funding two to six townhouses covers what lenders lend against once the project grows. If this is your first project of this kind, first development finance for owner-builders is a useful read on how lenders judge experience.
Tax is the other reason the line matters. The 2026-27 Budget negative gearing and capital gains tax factsheet limits the new treatment to dwellings that genuinely add to supply, and states that "Knock-down rebuilds or substantial renovations that do not increase supply will not be eligible". At the time of writing, the changes apply from 1 July 2027. In short, one home replaced with one home is not a new build, while a rebuild that replaces a house with more dwellings can be. The detailed definition may still change, so confirm your position with your accountant; our post on the new-build negative gearing change covers the timing questions.
A knock down rebuild is a crossover loan. The existing mortgage is restructured into a construction facility before demolition, the land carries the debt until the new home exists, and the build is drawn down in stages against an as if complete valuation. At completion, self-employed owners often refinance into a One Doc or low doc home loan. Approvals come before demolition, rent and interest are tested together, and once the plan becomes two or more dwellings, the file starts to look like development finance.
Key takeaway: settle the restructure of your existing loan before anyone books the excavator.Frequently Asked Questions
Whether it is cheaper to knock down and rebuild depends on the building contract, the costs that sit outside it, and how long you carry rent and construction interest at the same time. On the finance side, a rebuild keeps your land and avoids the buying costs of a new property, but it adds demolition, possible asbestos removal, rent and interest that grows with each drawdown. Our self-employed construction loan guide lists the cost lines to price before you compare options.
How long it takes to knock down and rebuild is usually measured in months, and the timeline varies with approvals and the builder. Approvals for the new home and the demolition can take as long as the build itself, and the lender will not fund demolition until both are in place. The builder's stages and the lender's staged drawdowns then set the pace of the build.
You can knock down and rebuild with an existing mortgage, but the loan has to be restructured into a construction facility before demolition, because the house securing it will no longer exist. Once the house is gone, the lender measures the loan to value ratio against the land alone. If the land does not cover the existing debt comfortably, you may need to pay it down or offer additional security first.
You finance a knock down rebuild with a construction loan secured on your land, which absorbs the existing mortgage before demolition and pays the builder in stages. At completion the construction loan converts or is refinanced into a standard home loan. Self-employed owners often use a One Doc home loan or low doc loan for that take-out, subject to lender policy.
A knock down rebuild counts as a new build for the negative gearing changes only where it adds to housing supply, according to the 2026-27 Budget factsheet. Replacing one home with one home is not a new build, while replacing a house with more dwellings can be. The detailed definition may still change, so confirm it with your accountant; our post on the new-build negative gearing change covers the timing.
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