How to fund an extension with a construction loan

A construction loan for an extension works by releasing funds progressively as each stage of your build is completed, rather than giving you the full amount upfront.

If you're planning to extend your Hamilton home, whether that's adding a second storey to a weatherboard near Beaumont Street or pushing out into the backyard of a cottage in the heritage precinct, you'll need a different type of finance than a standard home loan. Most banks and lenders won't hand over a lump sum for work that hasn't been done yet. Instead, they'll release funds in stages as your builder hits certain milestones, which protects both you and the lender from risk.

The structure can feel unfamiliar if you've only dealt with traditional mortgages before, but once you understand how the drawdown schedule aligns with your building contract, it becomes straightforward.

What makes a construction loan different from refinancing

A construction loan is tied to the progress of your build, not the purchase of a finished property. You only pay interest on the amount drawn down at each stage, rather than the full loan amount from day one. This means if your extension is funded in five progress payments over four months, your interest costs will gradually increase as more funds are released.

Refinancing your existing mortgage to release equity might cover the cost of an extension, but it won't be structured around your building timeline. You'd receive the full amount at settlement and start paying interest on it immediately, even if your builder won't need the first payment for weeks. For smaller projects where timing isn't critical, that might be fine. For anything over a few months, a construction loan typically makes more financial sense.

How the progressive drawdown actually works

Your builder will submit a progress claim after completing each stage, such as slab down, frame up, lockup, fixing, and practical completion. The lender will arrange a progress inspection, usually through a third-party valuer, to confirm the work has been done to the claimed stage. Once approved, the funds are released directly to the builder or to you, depending on how your contract is structured.

Most lenders charge a Progressive Drawing Fee for each inspection, typically between $300 and $500 per drawdown. That cost adds up across five or six stages, so factor it into your budget alongside council approval fees and any engineer or certifier costs.

Consider a homeowner extending a single-level home in Hamilton to add a second bedroom and ensuite. The fixed price building contract is set at $120,000, broken into five progress payments. After the slab is poured, the builder claims the first payment of $24,000. The lender inspects, approves, and releases the funds. At that point, the homeowner is only paying interest on $24,000, not the full loan amount. After the frame goes up, another $24,000 is drawn, and interest is now calculated on $48,000. The process continues until practical completion, when the final payment is released and the loan converts to principal and interest repayments, or continues on interest-only if that's been arranged.

Fixed price contracts and why lenders prefer them

Lenders want certainty. A fixed price building contract gives them that by locking in the total cost before construction begins. It also protects you from cost blowouts, which is why most banks won't approve a construction loan without one. Cost plus contracts, where you pay for materials and labour as they're invoiced, are harder to get finance for because the final cost isn't known upfront.

If you're using a registered builder, they'll typically provide a fixed price contract as standard. If you're planning to owner-build or use separate sub-contractors like plumbers and electricians, you'll need to demonstrate a detailed breakdown of costs and show you have the experience to manage the project. Most mainstream lenders won't touch owner builder finance without a strong case, and even then, they'll often cap the loan-to-value ratio lower than they would for a registered builder.

Council approval and timing requirements

Your development application needs to be approved before a lender will formally approve your construction loan. Some lenders will give you conditional approval while the DA is still with council, but they won't release any funds until you have stamped plans and can show that building can legally commence.

Once your loan is approved, most lenders require you to commence building within a set period from the disclosure date, usually six to twelve months. If your builder can't start within that window, your approval may lapse and you'll need to reapply. In Hamilton, where established homes often sit on larger blocks with heritage overlays or flood considerations, council approval can take longer than expected. Plan for that delay and make sure your builder's schedule aligns with your finance approval timeline.

What happens after the final drawdown

Once the final progress payment is made and practical completion is signed off, your construction loan converts to a standard home loan. If you've been on interest-only repayments during the build, you'll typically switch to principal and interest at this point, unless you've arranged to continue on interest-only for a set period.

Your repayments will increase once the full loan amount is active, so make sure you've budgeted for that shift. The loan amount will now include the original balance on your home plus the full cost of the extension, and your repayments will reflect that combined total. If you've used equity in your existing property to fund the deposit and costs, your overall borrowing capacity will determine how much you can comfortably repay without strain.

Using equity to fund the deposit and costs

Most construction loans require a deposit, typically around 10% to 20% of the total project cost, plus enough to cover upfront costs like council fees, engineer reports, and the first round of lender fees. If you've owned your Hamilton home for a few years and it's increased in value, you can often access that equity without needing to sell or use cash savings.

Equity is the difference between what your home is worth and what you owe on it. If your home is valued at $650,000 and you owe $400,000, you have $250,000 in equity. Lenders will typically let you borrow against up to 80% of your home's value without needing to pay lenders mortgage insurance, which means you could access around $120,000 of that equity to fund your extension deposit and costs. The exact amount depends on your income, existing commitments, and the lender's assessment of your situation.

Call one of our team or book an appointment at a time that works for you. We'll walk through your current position, confirm what your equity can cover, and structure the loan so the drawdown schedule matches your building contract without leaving you short at any stage.

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