How to Finance a Granny Flat: Loans, Equity & Funding Options

TL;DR: Most Australians finance a granny flat by tapping into their home equity (via a top-up, refinance or line of credit), which offers the lowest interest rates and simplest approval process. Construction loans are the next best option, releasing funds in stages as the build progresses. Personal loans work for smaller projects under $50,000 but carry higher interest rates. The key number is your LVR (Loan-to-Value Ratio) — you generally need at least 20% equity in your property to borrow without paying Lenders Mortgage Insurance. Commonwealth Bank is currently the most progressive of the Big Four for granny flat and prefab lending.

Key takeaways

• Home equity is the cheapest way to finance a granny flat, with variable rates from 5.8% to 6.5% (as of early 2026). You need sufficient equity: banks typically lend up to 80% of your property value minus your existing mortgage.
• Construction loans release funds in stages tied to build milestones. They require a licensed builder, a fixed-price contract, and council-approved plans.
• Personal loans suit small builds (under $50,000) but come with higher rates (7-14%) and shorter terms (5-7 years).
• CBA is leading the Big Four in granny flat lending, offering up to 60% of contract value during off-site prefab construction (80% for accredited manufacturers).
• A granny flat can add 20-30% to your property value and generate $200-$600/week in rental income, making the financing cost worthwhile for many homeowners.
• Use the grannyflatcost.com calculator to estimate your build cost, then work backwards to determine how much you need to borrow.

Financing options compared

Here is how the main financing pathways stack up for a typical granny flat build of $150,000-$250,000.

Option	Interest rate (indicative)	Loan term	Best for	Key requirement
Home equity top-up	5.8-6.5%	Up to 30 years	Most homeowners with equity	Sufficient equity (LVR below 80%)
Refinance	5.8-6.5%	Up to 30 years	Homeowners wanting a better rate	Willingness to switch lenders
Construction loan	6.0-7.0%	Up to 30 years	New builds with licensed builder	Fixed-price contract + approved plans
Line of credit	6.0-7.0%	Ongoing	Flexible drawdown needs	Property equity as security
Personal loan (secured)	7-10%	5-7 years	Smaller builds under $50k	Property or asset as security
Personal loan (unsecured)	9-14%	3-7 years	Very small projects, no equity	Good credit history

Option 1: Home equity (top-up or refinance)

This is the most common and cost-effective way to finance a granny flat. If your property has increased in value since you purchased it, or you have paid down a significant portion of your mortgage, you likely have usable equity.

How it works

Banks generally lend up to 80% of your property’s current value. The difference between that figure and your existing mortgage balance is your available equity.

Example:

• Property value: $800,000
• Existing mortgage: $450,000
• Maximum borrowing (80% LVR): $640,000
• Available equity: $640,000 - $450,000 = $190,000

In this example, you could borrow up to $190,000 for a granny flat without triggering Lenders Mortgage Insurance (LMI).

Top-up vs refinance

A top-up is the simpler option — you ask your current lender to increase your existing loan, no new application, no switching costs. The catch is you stay on your current interest rate, which may not be the best available.

Refinancing moves your entire mortgage (plus the granny flat funding) to a new lender offering a better rate or terms. More work, but it can save thousands in interest over the loan term if the rate difference is meaningful.

Pros

• Lowest interest rate of any financing option
• Longest repayment term (up to 30 years) keeps monthly repayments manageable
• Simple process if you have sufficient equity
• Interest may be tax-deductible if the granny flat is rented out (consult your accountant)

Cons

• Increases your total mortgage debt and extends your repayment period
• Requires a property valuation (typically $300-$600)
• If property values fall, you may not have enough equity
• The granny flat itself does not count toward your equity until it is built and the property is revalued

Option 2: Construction loan

A construction loan is designed specifically for building projects. Instead of receiving the full loan amount upfront, funds are released progressively at key construction stages (called “progress draws”).

How it works

1. You engage a licensed builder who provides a fixed-price building contract.
2. You apply for a construction loan with council-approved plans and the building contract.
3. The bank orders an “as if complete” valuation — estimating your property’s value with the finished granny flat.
4. Once approved, funds are released at agreed milestones (slab, frame, lock-up, fit-out, completion).
5. During construction, you typically pay interest only on the amount drawn down, not the full loan.

Progress draw schedule (typical)

Stage	Draw percentage	Cumulative
Deposit to builder	10%	10%
Slab/base complete	15%	25%
Frame complete	20%	45%
Lock-up	20%	65%
Fit-out complete	25%	90%
Practical completion	10%	100%

Pros

• You only pay interest on funds drawn, reducing costs during the build period
• Structured drawdowns align with builder progress payments
• Can be combined with your existing mortgage
• Available from most major lenders

Cons

• Requires a licensed builder and fixed-price contract (owner-builders may not qualify)
• More paperwork than a simple equity top-up
• The bank may charge a construction loan establishment fee ($500-$1,000)
• Each progress draw may require a bank inspection ($150-$300 per inspection)
• Minimum loan amounts apply (typically $20,000-$50,000 depending on lender)

Option 3: Line of credit

A line of credit (LOC) secured against your property lets you draw funds as needed up to an approved limit. You only pay interest on the amount you have actually drawn.

How it works

Your lender approves a credit limit based on your available equity. You draw funds when you need them — paying the builder, covering council fees — and repay at your own pace, as long as you meet minimum repayment requirements.

Pros

• Maximum flexibility: draw what you need, when you need it
• Interest rate is often lower than a construction loan
• No structured drawdown schedule to manage
• Can be left open for future needs

Cons

• The flexibility can lead to overspending if you are not disciplined
• Variable interest rates mean repayments can increase
• Some lenders charge annual fees for LOC facilities
• Not all lenders offer LOC products for granny flat construction

Option 4: Personal loan

For smaller granny flat projects — basic studios, kit home fit-outs, or topping up a shortfall from equity — a personal loan can fill the gap.

Secured personal loan uses your property, car or other asset as collateral. Lower interest rate (7-10%) and higher borrowing limits (up to $100,000+).

Unsecured personal loan requires no collateral. Higher interest rate (9-14%), lower limits (typically up to $50,000) and shorter terms.

Pros

• Fast approval (often within days)
• No property valuation required for unsecured loans
• Can be used for any part of the project, including owner-builder costs that banks may not cover
• Fixed repayments make budgeting straightforward

Cons

• Significantly higher interest rates than mortgage-based options
• Shorter repayment terms (3-7 years) mean higher monthly repayments
• Not cost-effective for builds over $50,000
• Interest is not tax-deductible even if the granny flat is rented out (as it is not a mortgage)

Which banks lend for granny flats?

Not all lenders treat granny flat construction equally. Here is the current landscape among the major banks.

Commonwealth Bank (CBA)

CBA is the most progressive of the Big Four for granny flat and prefab lending. As of January 2026, CBA will lend up to 60% of the total contract price during the off-site construction phase of a prefab build, and up to 80% for bank-accredited manufacturers. This matters because other banks only release funds once the prefab structure is fixed to the land.

CBA also offers standard construction loans for site-built granny flats using home equity.

Westpac, ANZ & NAB

These three currently only provide mortgage funds once the structure is permanently affixed to the land. For prefab or modular granny flats, this means you may need to fund the factory build phase yourself (or use a personal loan) before the bank releases construction loan funds.

NAB has indicated it is “considering how it can best support customers into this type of housing,” while Westpac has said there are “no planned changes” to its prefab loan structure.

Specialist and non-bank lenders

Mortgage brokers often have access to smaller lenders with more flexible granny flat policies. Some specialist lenders will fund owner-builder projects, builds on rural or irregular lots, higher LVR loans (up to 95% with LMI), and prefab builds during the factory phase.

A mortgage broker experienced in construction lending is often the best starting point for granny flat financing.

How LVR affects your borrowing

Your Loan-to-Value Ratio (LVR) is your total borrowing as a percentage of your property’s value. It is the most important number in granny flat financing.

LVR	What it means
Under 60%	Strong equity position. Best rates, easiest approval.
60-80%	Standard lending. Most banks will approve without LMI.
80-90%	LMI applies. Adds $5,000-$15,000+ to your borrowing cost.
Above 90%	Difficult to get approved. Limited lender options.

LMI: is it worth paying?

Lenders Mortgage Insurance is a one-off premium charged when your LVR exceeds 80%. On a $200,000 granny flat loan at 85% LVR, LMI could cost $5,000 to $10,000, added to your loan balance.

Whether LMI is worthwhile depends on your situation. If the granny flat will generate $300-$500/week in rent, the LMI cost is recouped within months. If it is for personal use (ageing parents, adult children), the equation is different and worth working through carefully.

Owner-builder financing challenges

If you plan to build the granny flat yourself as an owner-builder, financing is harder. Most banks require a licensed builder and a fixed-price contract for construction loans. Owner-builders provide neither.

Your options as an owner-builder are more limited. An equity top-up or refinance is the simplest route — draw funds as a lump sum against your equity, no builder contracts required. For smaller components, a personal loan can fill gaps. Many owner-builders fund a significant portion from savings to avoid lending complications altogether. Some non-bank lenders offer owner-builder construction loans with modified conditions, such as requiring an independent building inspector at each stage.

Owner-builders also face permit fees (NSW $219, VIC $110, QLD $462), no builder warranty (you warrant the work, which affects resale and insurance), and potentially higher interest rates due to perceived lender risk.

Government grants and subsidies

Direct government grants for granny flats are limited in Australia, with one notable exception.

Queensland First Home Owner Grant ($30,000)

Queensland’s FHOG of $30,000 explicitly covers granny flats or tiny homes built on a relative’s land, provided:

• The contract to build is in your (the first home buyer’s) name
• The total value (including land) is under $750,000
• It is your principal place of residence
• Contracts must be signed before 30 June 2026

This is the most significant direct grant available for granny flat construction in Australia.

Victoria: reduced approval costs

Victoria’s planning reforms mean granny flats up to 60 sqm generally no longer require a planning permit. While not a cash grant, this saves $1,500-$5,000 in planning application fees and weeks of approval time.

No federal grant

There is currently no federal-level grant specifically for granny flats. The earlier HomeBuilder grant (which excluded granny flats) ended in 2022.

Potential tax benefits

If you rent out the granny flat, you can claim depreciation, interest on the loan used for construction, and maintenance costs as tax deductions. Since 1 July 2021, certain granny flat arrangements — where an older person contributes to the build in exchange for a right to live there — are exempt from Capital Gains Tax, provided specific conditions are met. If your rental income is less than your loan interest and expenses, the loss can reduce your taxable income through negative gearing.

Consult a tax accountant for advice specific to your situation.

Cost vs value: does financing make sense?

A granny flat typically costs $150,000 to $300,000 to build. Here is how the numbers work for a common scenario.

Example: $200,000 build financed via equity top-up

Item	Amount
Build cost	$200,000
Interest rate	6.2% variable
Loan term	25 years
Monthly repayment	~$1,330
Total interest paid	~$199,000

If rented at $400/week

Item	Amount
Annual rental income	$20,800
Annual loan repayments	$15,960
Annual net cash flow (before tax/expenses)	+$4,840
Property value increase (est. 20-30%)	$160,000 - $240,000 on an $800k property

In this scenario, the granny flat pays for itself through rental income while simultaneously increasing your property value by potentially more than the build cost.

When financing does not make sense

• Your LVR is already above 80% and LMI would be significant
• You plan to sell the property within 2-3 years (not enough time to recoup costs)
• The granny flat will not be rented and you do not need the space
• Your property is in an area with poor rental demand
• You are already under financial stress from your existing mortgage

Documents you will need

Regardless of which financing option you choose, have these documents ready to speed up the process.

For all loan types

• Proof of income (2 most recent payslips, or 2 years of tax returns for self-employed)
• Existing mortgage statements
• Bank statements (3-6 months)
• Property rates notice
• Photo ID

Additional for construction loans

• Council-approved plans
• Fixed-price building contract with a licensed builder
• Builder’s licence number and insurance certificates
• Quantity surveyor report (some lenders require this)
• Evidence of council approval or CDC

Additional for equity access

• Recent property valuation or comparable sales evidence
• Details of any property improvements since purchase

Next steps

1. Estimate your build cost. Use the grannyflatcost.com calculator to get a realistic figure for your area, build type and size.
2. Calculate your available equity. Check your latest mortgage statement and get an approximate current property value from recent comparable sales.
3. Talk to a mortgage broker. A broker experienced in construction lending can compare options across multiple lenders and find the best fit for your situation.
4. Get your documents in order. Having everything ready before you apply speeds up the process significantly.
5. Get 3+ builder quotes. Lenders need a fixed-price contract for construction loans, so engaging builders early in the process is essential.