Unlock the secrets to construction finance for duplexes

Construction finance for a duplex development works differently to a standard home loan.

You're borrowing against a completed asset that doesn't yet exist, which means lenders assess both the land value and the end value of the project. The loan is released progressively as the build advances, and you'll only pay interest on what's been drawn down so far. For oncology pharmacists considering a duplex build, whether as an investment or a live-in-one-rent-one strategy, understanding how the drawdown structure works and what lenders require at application stage will determine whether the project stacks up financially before you commit to council plans.

How Construction Loans Differ from Standard Mortgages

A construction loan releases funds in stages tied to building milestones rather than as a lump sum at settlement. Lenders assess your application based on the combined land value and the estimated end value of the completed duplex, which means you'll need a detailed cost breakdown from a registered builder before approval. You only pay interest on the amount drawn down at each stage, not the full loan amount, which reduces your repayment burden during the build. Once construction is complete, the loan typically converts to a standard principal and interest or interest-only mortgage without requiring a new application.

What Lenders Assess at Application

Lenders want to see a fixed price building contract from a registered builder, council approval for the development, and confirmation that the land is suitable for the proposed build. Your borrowing capacity is assessed on your current income, not projected rental income from the completed duplex, which means your salary as an oncology pharmacist will carry the application. Most lenders require a deposit of at least 10% of the total project cost, though some will accept higher loan-to-value ratios if you're using equity from an existing property. The valuation is based on 'as if complete' value, meaning the lender's valuer estimates what the finished duplex will be worth, not just the vacant land.

Consider a scenario where you've found suitable land and engaged a builder for a duplex project with a total cost of around $850,000, including land, construction, and associated fees. The lender orders an 'as if complete' valuation that comes back at $920,000. Your application is assessed on the $850,000 project cost, and with a 15% deposit of $127,500, you're borrowing $722,500. Because you're earning a full-time salary and have no other investment debt, your income comfortably services the interest-only repayments during construction. The fixed price building contract removes cost uncertainty, and council approval is already in place, so the lender can assess the risk accurately.

How the Progressive Drawdown Schedule Works

Funds are released at specific stages of construction, typically slab down, frame up, lockup, fixing, and completion. Each drawdown requires a progress inspection by the lender's valuer or a third-party inspector to confirm the stage has been reached. The builder submits an invoice for that stage, the inspection is completed, and the lender releases funds directly to the builder or into your nominated account depending on the contract structure. Between drawdowns, you're charged interest only on the amount already released, which keeps repayments lower during the build period compared to borrowing the full amount upfront.

If the first drawdown is $150,000 for slab and early framing, your interest repayment for that month is calculated on $150,000, not the full $722,500 loan amount. As each subsequent stage is completed and drawn, your interest repayment increases incrementally. This structure means your repayments grow over the course of the build, so budgeting for the increasing cost is important if you're still covering rent or a mortgage on another property during construction.

Fixed Price Contracts and Cost Control

Most lenders will only approve construction finance against a fixed price building contract, which protects both you and the lender from cost blowouts. A cost plus contract, where you're billed for actual costs plus a builder's margin, introduces uncertainty that makes lenders uncomfortable. The fixed price contract should specify exactly what's included in the build, from site preparation through to landscaping and driveways, so there's no ambiguity at drawdown stage about whether a cost falls within the contract or is a variation.

Variations during construction can affect your funding if they push the total project cost above what the lender approved. If you decide mid-build to upgrade finishes or add features that weren't in the original contract, you'll need to cover those costs from your own funds unless you apply for a loan increase, which requires a new valuation and credit assessment. Keeping variations minimal protects your contingency buffer and avoids funding gaps during the build.

Land and Construction Package Versus Separate Contracts

Some developers offer a combined land and construction package, where you purchase the land and contract the builder in a single transaction. This can simplify the process, but you'll still need separate settlement for the land and progressive drawdown for the construction. If you're purchasing land separately and engaging your own builder, you'll settle on the land first, then activate the construction loan once council approval and the building contract are in place. Both approaches work for construction finance, but the separate path gives you more control over builder selection and design.

For duplex developments, council approval is often the longest part of the timeline, not the build itself. Lenders typically require you to commence building within a set period from the loan disclosure date, often six to twelve months, so it's worth securing development application approval before you finalise finance. If council approval drags out and you can't start the build within the lender's timeframe, you may need to reapply or extend the approval period, which can delay the project.

Interest-Only Repayment Options During Construction

Most construction loans allow interest-only repayments during the build, which keeps your monthly cost lower while funds are being progressively drawn. Once construction is complete and the loan converts to a standard mortgage, you can choose to continue with interest-only if you're treating the duplex as an investment, or switch to principal and interest repayments if you're planning to live in one half. Interest-only repayments can be structured for up to five years in some cases, depending on the lender and your circumstances.

If you're planning to retain the duplex as an investment property after completion, the interest-only structure during construction rolls naturally into an ongoing investment loan strategy. If you're planning to occupy one half, switching to principal and interest repayments post-construction reduces the loan balance over time and builds equity faster, which can be useful if you're planning further development or property purchases down the line.

Progressive Drawing Fees and Inspection Costs

Lenders charge a progressive drawing fee each time funds are released, typically between $150 and $400 per drawdown depending on the lender. Over a five-stage build, that's an additional cost of up to $2,000 that sits outside the construction contract. Some lenders also charge for progress inspections, while others include a set number of inspections in the loan package. These fees are usually deducted from the drawdown amount or charged to your loan account, so you don't need to pay them upfront, but they do add to the total project cost.

Budgeting for these fees at the outset, along with council approval costs, planning fees, and any consultant charges for soil tests or engineering reports, gives you a more accurate picture of total project cost. Underestimating the non-construction costs is a common issue that can leave you short at settlement if your contingency buffer is too thin.

When Owner Builder Finance Applies

If you're planning to manage the build yourself as an owner builder rather than engaging a registered builder, your finance options narrow significantly. Most mainstream lenders won't provide construction finance for owner builder projects because the risk of cost blowout or incomplete work is higher without a licensed builder's warranty. Specialist lenders do offer owner builder finance, but the rates are typically higher and the loan-to-value ratio is lower, often capped at 70% to 80% of project cost. For oncology pharmacists with demanding clinical schedules, acting as owner builder on a duplex development is generally not practical, but it's worth knowing the distinction if you're comparing options.

How Equity from Existing Property Can Fund Your Deposit

If you already own property, you can use equity to cover the deposit and associated costs for the duplex development without selling or needing cash savings. Equity release works by refinancing your existing property to access the difference between its current value and what you owe, which can then be used as a deposit for the construction project. Lenders will assess your total debt position across both properties, so your income needs to service the combined loan amounts, but this approach lets you start the build without liquidating other assets.

In our experience, using equity from a well-performing property to fund a duplex development is a common strategy for pharmacists looking to expand their portfolio without waiting years to save a cash deposit. The key is ensuring your income can service the interest on both loans during construction, and that the completed duplex will either generate rental income or reduce your overall housing cost if you plan to occupy one half.

Links Between Construction Finance and Broader Investment Strategy

If the duplex is your first investment property, understanding how construction finance fits within a longer-term portfolio plan is worth considering before you commit. Building your first investment property using construction finance gives you a new asset at current replacement cost, which can offer better value than buying established property in some markets, but it also locks you into a build timeline and requires active project management. If you're planning to expand your property portfolio over time, starting with a duplex development can accelerate equity growth if the end value exceeds total project cost, but it also concentrates risk in a single project rather than spreading it across multiple properties.

Call one of our team or book an appointment at a time that works for you. We'll walk through your duplex project in detail, confirm what lenders will assess at application, and structure the construction drawdown to match your build timeline and cash flow.

Frequently Asked Questions