Financing an extension through a construction loan involves progressive drawdown tied to building milestones rather than a single upfront settlement.
The lender releases funds in instalments as your registered builder completes stages like base, frame, lock-up, and fixing, with each release requiring a progress inspection before approval. You pay interest only on the amount drawn down at each stage, not the full loan amount, which reduces early repayment costs during the build period. Understanding how this differs from a standard home loan helps avoid delays, unexpected costs, and approval issues during the project.
Construction Loans Release Funds in Stages
A construction loan for an extension provides funds through a progressive drawdown schedule aligned with your building contract milestones. The lender holds the approved loan amount and releases it as your builder reaches agreed stages, typically base, frame, lock-up, fixing, and practical completion. Before each release, the lender arranges a progress inspection to confirm the work matches the claim, then transfers funds directly to the builder or into your account depending on the contract structure.
This differs from renovation finance using a standard home loan, where you receive the full amount at settlement and manage payments yourself. With construction loans, the lender controls the flow of funds to reduce risk, which adds approval steps but protects both you and the lender from incomplete work or cost blowouts.
Interest Accrues Only on Drawn Amounts
During the construction period, you pay interest only on the funds released to date, not the full approved loan amount. If your extension is approved for $150,000 and the first draw is $30,000 for the base stage, your interest charges apply only to that $30,000 until the next stage is completed and funds are released. Most lenders offer interest-only repayment options during construction, which keeps costs lower while the work is underway.
Once the extension reaches practical completion, the loan typically converts to principal and interest repayments based on the full drawn amount. Lenders charge a Progressive Drawing Fee for each inspection and release, usually between $200 and $400 per drawdown, so a five-stage build will add around $1,000 to $2,000 in fees to the total project cost.
Fixed Price Building Contracts Are Required
Most lenders will only approve construction finance for extensions when you have a fixed price building contract with a registered builder. The contract must specify the total cost, itemised Progress Payment Schedule, and completion timeframe, giving the lender certainty over the project scope and cost. Cost plus contracts, where the builder charges actual costs plus a margin, are rarely accepted because the final price remains variable and increases lender risk.
You will also need council approval and stamped plans before the loan application can proceed. The lender reviews the contract, plans, and builder's credentials as part of the assessment, so delays in securing council plans or choosing a builder will delay your finance approval. If you are acting as an owner builder, approval becomes more difficult and often requires a larger deposit or additional equity in the property.
Avoid Assuming Your Current Lender Will Approve the Extension
Your existing home loan lender may not offer construction finance or may impose stricter criteria for extensions than a new lender would. Some lenders do not provide progressive drawdown facilities at all, while others limit them to full new home construction rather than renovations or extensions. If your current lender does not support construction loans, you will need to refinance to a lender that does, or take out a separate construction facility and manage two loans during the build.
Consider a homeowner with $400,000 owing on their mortgage who wants to add a $120,000 extension. Their current lender may not offer construction finance, so they refinance the full $520,000 to a lender that provides a construction to permanent loan. The new loan includes a $120,000 construction component with progressive drawdown and a $400,000 standard component, both converting to a single ongoing home loan once the build is complete. This avoids split facilities and simplifies repayments after practical completion.
Building Must Commence Within a Set Period
Most construction loan approvals require you to commence building within a set period from the Disclosure Date, usually three to six months. If the build does not start within that window, the approval may lapse and require resubmission, particularly if your financial circumstances or the property valuation have changed. Delays in securing a builder, finalising council approval, or resolving site issues can push the start date beyond the allowable period and force a new application.
Once construction begins, lenders also expect the project to reach practical completion within the timeframe stated in the building contract, typically six to twelve months for an extension. If the build runs over schedule, you may need to request an extension of the interest-only period or provide updated documentation to the lender. Builders who miss deadlines or subcontractors who delay stages can create additional costs and complicate drawdown timing, so choosing a registered builder with a solid record reduces these risks.
Equity in the Property Affects Approval
Lenders assess your application based on the combined value of your existing property plus the completed extension, not the current value alone. If your home is worth $600,000 and the extension will add $120,000 in value, the lender uses $720,000 as the security value when calculating your loan-to-value ratio. You will need sufficient equity in the property to support the total loan amount, plus the ability to service the higher repayments once the loan converts to principal and interest.
If your equity is tight, the lender may require a higher deposit, restrict the loan amount, or decline the application altogether. This is common when the extension cost is high relative to the current property value, or when your existing mortgage is close to the property's current worth. In these cases, you may need to contribute cash savings to the project or reduce the scope of the extension to fit within the lender's risk appetite.
Call one of our team or book an appointment at a time that works for you to discuss how a construction loan can be structured for your extension project.
Frequently Asked Questions
Do I pay interest on the full loan amount during construction?
No, you only pay interest on the amount drawn down at each stage. If $30,000 has been released for the base stage, interest applies only to that amount until the next drawdown occurs.
Can I use my current lender for a construction loan on an extension?
Not always. Some lenders do not offer progressive drawdown facilities or restrict them to new builds rather than extensions. You may need to refinance to a lender that provides construction finance.
What happens if my builder delays the project?
If the build runs over schedule, you may need to extend the interest-only period or provide updated documentation. Delays can also affect drawdown timing and increase holding costs during construction.
Do I need a fixed price building contract for approval?
Yes, most lenders require a fixed price contract with a registered builder and an itemised progress payment schedule. Cost plus contracts are rarely accepted due to variable final costs.
How long do I have to start construction after loan approval?
Most lenders require you to commence building within three to six months from the Disclosure Date. If the build does not start within that period, the approval may lapse and require resubmission.
