How construction finance works for extensions
A construction loan for an extension works differently to a standard mortgage. The lender releases funds in stages as your builder completes defined milestones, and you only pay interest on what has been drawn down so far. This structure protects both you and the lender, but it requires detailed documentation upfront and coordination with your builder throughout the project.
In Victoria, most lenders require council approval before they will assess your application. That means you need to have submitted a development application and received planning approval before applying for finance. The construction loan application also requires a signed fixed price building contract with a registered builder, a detailed cost breakdown, and evidence that your builder holds appropriate insurance.
The progressive drawdown structure
Funds are released according to a progress payment schedule, typically in five or six stages. The first drawdown often occurs at slab or base stage, followed by frame stage, lock-up, fixing, and completion. Before each payment, the lender arranges a progress inspection to confirm that the work claimed has actually been completed to the required standard. Once the inspector approves the stage, the funds are released directly to your builder.
This progressive drawdown means you are not paying interest on the full loan amount from day one. Consider an ADF member in Geelong extending their home with a $150,000 build. If the first stage drawdown is $30,000, they are charged interest only on that amount until the next stage is completed and the next payment is made. Over a six-month build, this can make a measurable difference to the total interest paid compared to drawing the full amount upfront.
Most lenders also charge a progressive drawing fee each time funds are released. This fee typically ranges from $150 to $300 per drawdown, so over five stages you might pay $750 to $1,500 in total. Factor this into your budget when calculating the total cost of your extension.
What lenders require before approval
Lenders assess construction loan applications more thoroughly than standard home loan applications. They want to see that your project is viable, that your builder is credible, and that you have enough equity or deposit to cover cost overruns.
You will need council plans that match your development application, a fixed price building contract that specifies the scope of work and payment schedule, proof that your builder is registered and insured, and a detailed cost breakdown from your builder. The lender will also require a valuation that includes the estimated value of your property once the extension is complete. If that end valuation does not support the loan amount you are requesting, you may need to reduce the scope of the project or contribute more of your own funds.
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How your existing equity affects borrowing capacity
If you own your home outright or have paid down a portion of your mortgage, you can use that equity to fund your extension. The lender calculates how much you can borrow based on the projected value of your property after the extension is complete, not its current value.
As an example, an ADF member in Ballarat owns a home with no mortgage remaining. The property is currently valued in the mid-range for the area. They want to add a second storey with two bedrooms and a bathroom. The build cost is quoted at $180,000. Once complete, the valuation estimates the property will be worth significantly more. The lender assesses the loan against the completed value, and because the member has full equity in the existing property, they can borrow the full build cost without needing to access their savings. Repayments begin once the extension is finished and the loan converts to a standard principal and interest mortgage.
This approach works well if you have built up equity over time, but if you still owe a substantial amount on your existing mortgage, your borrowing capacity will be limited. The lender will consider your total debt position, not just the equity available for the extension. If you are close to your borrowing limit, you may need to contribute savings or reduce the scope of the build.
Interest-only repayments during construction
During the construction period, most lenders offer interest-only repayment options. You pay interest only on the amount drawn down so far, and once the build is complete, the loan typically converts to principal and interest repayments over the remaining term.
This structure keeps your repayments lower during the build, which is helpful if you are also paying rent elsewhere or covering other temporary costs while the work is underway. However, once the loan converts, your repayments will increase because you are now paying down the principal as well as the interest. Plan for that increase before you commit to the project.
The role of Defence Home Ownership Assistance Scheme benefits
If you are an ADF member who has not yet used your Defence Home Ownership Assistance Scheme subsidy, you cannot typically apply it to a construction loan during the build phase. The subsidy is designed to reduce mortgage repayments on a standard home loan, not on interest-only construction finance. However, once your construction loan converts to a principal and interest home loan, the subsidy can apply if you meet the eligibility criteria.
Some ADF members in Victoria choose to fund their extension using a standard equity release loan instead of a construction loan. This approach involves borrowing the full amount upfront and paying it to the builder in stages yourself. It avoids progressive drawing fees and allows the subsidy to apply immediately, but it also means you are paying interest on the full loan amount from day one. Whether this makes sense depends on the size of your build, how quickly it will be completed, and whether the progressive drawing fees outweigh the additional interest cost.
Fixed price contracts and cost overruns
A fixed price building contract locks in the total cost of your extension, provided the scope of work does not change. If you decide halfway through the build that you want to upgrade the kitchen or add another window, those variations will increase the price, and you will need to cover the additional cost yourself unless you arranged a buffer in your original loan amount.
Most brokers recommend borrowing slightly more than the quoted build cost to cover variations, unforeseen site conditions, or minor changes during construction. If you borrow exactly the amount quoted and the project runs over budget, you will either need to find additional funds or negotiate a reduced scope with your builder. A buffer of five to ten percent is common, but check with your lender how much flexibility they allow and whether they will approve a loan amount above the fixed contract price.
Builder insurance and registration requirements
In Victoria, any builder working on a project over a certain value must be registered and must provide domestic building insurance. This insurance protects you if the builder becomes insolvent or fails to complete the work. Lenders will not approve a construction loan unless the builder holds this insurance and provides proof of registration.
Before signing a contract, confirm that your builder is registered with the Victorian Building Authority and that they can provide a certificate of insurance that covers the full contract value. If they cannot, the lender will not proceed, and you will need to find another builder. This requirement exists to protect both you and the lender, and it is not negotiable.
When the loan converts to a standard mortgage
Once the final inspection is completed and the extension is signed off, your construction loan converts to a standard principal and interest mortgage. The conversion usually happens automatically, and your repayments adjust to reflect the full loan amount over the agreed term.
At this point, you can also consider whether to refinance into a different loan product. If interest rates have shifted since you started the build, or if you want to access features like an offset account or redraw facility, conversion is the right time to review your options. Some lenders offer home loan refinancing with benefits specific to ADF members, including waived application fees or reduced rates, so it is worth comparing what is available before you settle into the converted loan.
Call one of our team or book an appointment at a time that works for you. We work with lenders across Australia who understand how construction finance applies to extension projects, and we can help you structure a loan that fits your equity position, build timeline, and repayment capacity.
Frequently Asked Questions
How does a construction loan work for a home extension?
A construction loan releases funds in stages as your builder completes defined milestones, and you only pay interest on the amount drawn down so far. The lender requires council approval, a fixed price building contract, and a progress inspection before each payment is made.
Can I use equity in my current home to fund an extension?
You can use equity in your current home to fund an extension, and the lender will assess your borrowing capacity based on the projected value of your property once the extension is complete. If you still owe a substantial amount on your existing mortgage, your borrowing capacity will be limited.
What happens if my extension project goes over budget?
If your extension goes over budget due to variations or unforeseen costs, you will need to cover the additional expense yourself unless you arranged a buffer in your original loan amount. Most brokers recommend borrowing five to ten percent more than the quoted build cost to cover potential overruns.
Do I pay interest on the full loan amount during construction?
You only pay interest on the amount drawn down so far during construction, not on the full loan amount. Most lenders offer interest-only repayments during the build, which convert to principal and interest repayments once the extension is complete.
What builder documentation do lenders require in Victoria?
Lenders require a fixed price building contract, proof that your builder is registered with the Victorian Building Authority, and evidence of domestic building insurance. They also require council plans that match your development application and a detailed cost breakdown from your builder.
