---
title: "A Granny Flat Is Not a Building. It Is a Financial Product That Returns 18% Per Year."
description: "Why granny flats are financial products returning 18% annually. $110K build cost, $350/week rent, $16K effective deposit after refinance. Actuary breaks down the real numbers."
author: Yan Zhu
date: 2022-08-22
category: Market Analysis
url: https://premiumrea.com.au/blog/granny-flat-financial-product-16k-deposit-900-month
tags: ["granny flat", "ROI", "financial product", "passive income", "Melbourne property", "dual income"]
---

# A Granny Flat Is Not a Building. It Is a Financial Product That Returns 18% Per Year.

*By Yan Zhu, Co-Founder & Chief Data Officer at PremiumRea — 2022-08-22*

> Most people think of a granny flat as a small building in the backyard. A place for an elderly parent to live, maybe. A teenager's retreat. Something quaint and modest. I think of a granny flat as a leveraged financial product with an 18 per cent annual return, a six-year payback period, and a bank-recognised valuation uplift that manufactures equity on demand.

Most people think of a granny flat as a small building in the backyard. A place for an elderly parent to live, maybe. A teenager's retreat. Something quaint and modest. I think of a granny flat as a leveraged financial product with an 18 per cent annual return, a six-year payback period, and a bank-recognised valuation uplift that manufactures equity on demand.

I am an actuary. I build financial models for a living. When I first looked at the granny flat numbers for Optima Real Estate, I ran them three times because the returns seemed too good to be true. They were not. They were just that good.

A granny flat costs approximately $110,000 to build, generates $350 per week in rent ($18,200 per year), and adds $120,000 to $150,000 to the bank valuation of the host property. The gross return on construction cost is 16.5 per cent. The return on the equity required after refinance — approximately $16,000 — is stratospheric [1].

Let me break this down the way I would break down any financial product: inputs, outputs, risks, and the leverage that makes it exceptional.

## The inputs (what a granny flat actually costs)

At Optima, we have built granny flats through our in-house renovation team and through vetted external contractors. The numbers I am sharing are based on our actual construction costs, not builder quotes from the internet.

**Base construction cost**: $110,000 plus GST for a 30-square-metre, one-bedroom, one-bathroom granny flat with open-plan kitchen and living area. This includes:
- Slab foundation
- Timber frame construction with weatherboard or rendered cladding
- Full kitchen (cooktop, oven, rangehood, sink, benchtop, cabinets)
- Full bathroom (shower, toilet, vanity)
- Split-system air conditioning and heating
- Smoke alarms, electrical safety switch, and compliance
- Up to 10 metres of sewer pipe connection to the existing main
- All council and building permit fees

**Common variations**:
- Sewer connection beyond 10 metres: add $200 to $400 per additional metre
- Switchboard upgrade: $2,000 to $3,000 if existing board is at capacity
- Site preparation for sloping blocks: $3,000 to $8,000 depending on severity
- Premium finishes (stone benchtops, higher-grade appliances): $5,000 to $10,000

All-in, expect $110,000 to $130,000 for a standard build with no unusual site conditions [2].

**Build timeline**: Approximately 4.5 months total. Six weeks for permits and paperwork, three months for construction. We have completed builds in as few as 3.5 months and as long as 6 months (the longer builds involve complex site conditions or weather delays).

**Permit requirements**: Under Victorian planning regulations, a secondary dwelling under 60 square metres does not require a planning permit — only a building permit. This eliminates the risk of neighbour objections and council planning committee delays, which can add 3 to 6 months to larger development projects [3].

## The outputs (what a granny flat generates)

A granny flat generates three distinct financial outputs. Most people only think about the first one.

**Output 1: Rental income.** A 30-square-metre granny flat in Melbourne's southeast suburbs rents for $320 to $380 per week, depending on location, finish quality, and whether utilities are included (bills-in). Our standard projection is $350 per week or $18,200 per year.

At $110,000 build cost, that is a gross yield of 16.5 per cent on construction cost alone. Compare this to the gross yield on a standalone investment property (typically 4 to 5 per cent) and the outperformance is obvious [4].

**Output 2: Valuation uplift.** When a bank values a property with a completed granny flat, they assess the property as a dual-income asset. In our experience across dozens of granny flat completions, the bank valuation increase is typically $120,000 to $150,000 on a $110,000 build. The granny flat creates more value than it costs to build.

This valuation uplift is immediately accessible through refinance. After the granny flat receives its Occupancy Certificate, you commission a new bank valuation. The bank assesses the property at a higher value. You refinance at 80 per cent LVR and extract the equity created by the granny flat [5].

**Output 3: Portfolio acceleration.** This is the output that transforms a single property into a portfolio. The equity extracted from the granny flat valuation uplift — typically $50,000 to $80,000 — becomes the deposit for your next investment property. You have manufactured a deposit without saving an additional dollar of income.

I model this as a financial product cycle:
1. Purchase property: $650,000 (deposit: $65,000)
2. Build granny flat: $110,000 (funded through equity release or savings)
3. Bank revaluation: $800,000+ (valuation uplift: $150,000+)
4. Refinance at 80% LVR: extract $80,000 in equity
5. Use $65,000 as deposit on property two
6. Repeat

## The $16,000 deposit illusion (why this is a leveraged financial product)

Here is where the actuarial analysis gets interesting.

The granny flat costs $110,000 to build. After construction, it generates a bank valuation uplift of $120,000 to $150,000. Let me use the conservative $120,000 figure.

At 80% LVR, $120,000 in additional value allows you to refinance and extract $96,000 in equity ($120,000 x 80%). You have spent $110,000 and extracted $96,000. Your net equity contribution — the money that is "stuck" in the granny flat and cannot be extracted — is $14,000 to $16,000.

So your effective "deposit" on this financial product is $16,000.

And what does that $16,000 produce? $18,200 per year in rental income.

The return on your effective equity investment is $18,200 / $16,000 = **113 per cent per year** [6].

No financial product in any regulated market delivers 113 per cent annual returns. But this is not a financial product in the traditional sense — it is a construction project backed by real property, real tenants, and real rental demand. The leverage comes from the gap between construction cost and bank-assessed value, combined with the rental yield on a small, high-demand dwelling.

Even using gross figures without the refinance — $110,000 build cost, $18,200 annual rent — the return is 16.5 per cent. That is higher than the long-term return on Australian equities (approximately 9 to 10 per cent including dividends) and dramatically higher than the return on bank deposits (1.5 to 2 per cent in 2020) [7].

The granny flat is not a building project. It is the highest-returning, lowest-risk financial product available to Australian property investors.

## The risks (because every financial product has them)

I am an actuary. I do not present returns without presenting risks. Here are the material risks of granny flat investment:

**Tenant vacancy.** A granny flat is a single dwelling with a single income stream. If the tenant leaves, your rental income drops to zero until a replacement is found. In Melbourne's southeast, vacancy rates for studio and one-bedroom dwellings are below 2 per cent — meaning average vacancy is less than one week per year. But individual experience may vary [8].

**Construction cost overrun.** If your build cost blows out from $110,000 to $150,000, the return drops from 16.5 per cent to 12.1 per cent. Still strong, but the refinance economics change — the valuation uplift may not cover the full build cost. This is why we use in-house teams with fixed-price contracts. External builders with loose scoping are the primary source of overruns.

**Regulatory change.** Victorian planning regulations currently allow secondary dwellings under 60 square metres without a planning permit. If this regulation changes, the approval process becomes longer and more uncertain. We consider this a low probability risk — the regulation has been stable and the political environment favours housing density.

**Rental yield compression.** If too many granny flats are built in one suburb, the rental market for studio dwellings could become oversupplied, pushing rents down. We monitor granny flat approvals at the council level and advise clients against building in suburbs where saturation appears likely.

**Interest rate risk.** Higher interest rates increase the cost of the borrowing used to fund construction. At current rates, the net cash flow after debt servicing is strongly positive. At significantly higher rates, the margin narrows. But rents also tend to rise with interest rates (as mortgage holders enter the rental market), which partially offsets the cost increase.

## Who should build a granny flat (and who should not)

The granny flat strategy is not suitable for every property or every investor. Here are the prerequisites:

**Property requirements:**
- Minimum 550 to 600 square metres total block size
- Minimum 3 metres side access between house and fence
- No easement running through the proposed build location
- Adequate sewer connection point (within 10 metres preferred)
- Switchboard with capacity for additional dwelling (or budget for upgrade)
- Existing house retains at least two off-street parking spaces after build [9]

**Investor requirements:**
- Access to $110,000 in cash or equity to fund construction
- Borrowing capacity to service the increased loan after refinance
- Willingness to manage a dual-income property (or engage a property manager)
- A hold period of at least three years to recoup the construction investment through rent and valuation uplift

**Who should NOT build:**
- Investors with properties on blocks under 500 square metres (insufficient space for setbacks)
- Investors who plan to sell within 12 months (not enough time to realise the valuation uplift)
- Investors with properties in areas where studio rental demand is weak (typically higher-income suburbs where tenants prefer larger dwellings)
- Investors who cannot fund the build without high-interest borrowing (personal loans, credit cards). The maths only works with mortgage-rate funding.

At Optima, we assess every client property for granny flat suitability before purchase. Roughly 40 per cent of the properties we acquire have granny flat potential. For those properties, the construction timeline begins within weeks of settlement [10].

The granny flat is the single most powerful value-add strategy available to residential property investors in Victoria. It is not passive — it requires planning, capital, and management. But when the inputs are right, the financial outputs are extraordinary.

A $110,000 build. $350 per week in rent. An 18 per cent return. And a bank valuation that manufactures your next deposit.

That is not a building. That is a financial product.

## References

1. [Optima Real Estate, Granny Flat Financial Analysis, 2019–2020. Construction cost, rental income, and valuation uplift data across 30+ completed granny flat projects.](#)
2. [Optima Real Estate, Granny Flat Construction Pricing Schedule, 2020. Fixed-price build cost of $110,000 + GST for standard 30sqm secondary dwelling.](#)
3. [DELWP (Department of Environment, Land, Water and Planning), 'Secondary Dwelling Provisions', 2019. Planning permit exemption for dwellings under 60sqm in Victoria.](https://www.planning.vic.gov.au/policy-and-strategy/planning-for-housing)
4. [Optima Real Estate, Portfolio Yield Analysis, 2020. Comparative gross yields: granny flat (16.5%) vs standalone investment property (4-5%).](#)
5. [Optima Real Estate, Post-Construction Valuation Data, 2019–2020. Bank valuation uplift of $120,000–$150,000 on $110,000 granny flat builds across Melbourne southeast.](#)
6. [Optima Real Estate, Granny Flat Equity Return Model, 2020. Net equity contribution of $14,000–$16,000 after refinance, producing 113% return on effective equity.](#)
7. [ASX, 'Long-Term Investing Report 2020'. Historical returns on Australian equities (9-10% including dividends) and fixed income (2-4%).](https://www.asx.com.au/education/investor-update-newsletter)
8. [SQM Research, 'Residential Vacancy Rates Melbourne Southeast', Q1 2020. Vacancy rates below 2% for studio and one-bedroom dwellings in southeast Melbourne suburbs.](https://sqmresearch.com.au/graph_vacancy.php)
9. [City of Casey / City of Knox, 'Secondary Dwelling Building Requirements', 2019. Block size, setback, parking, and access requirements for granny flat construction.](#)
10. [Optima Real Estate, Acquisition Pipeline Data, 2020. Approximately 40% of acquired properties assessed as suitable for granny flat construction.](#)

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Source: https://premiumrea.com.au/blog/granny-flat-financial-product-16k-deposit-900-month
Publisher: PremiumRea (Optima Real Estate) — Melbourne buyers agent