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How much does a granny flat cost?

$15,000 - $250,000

    How much does it cost to build a granny flat?

    Granny flats are becoming increasingly popular in Australia. Beyond its original purpose for aging family members, having this home extension built can provide you with a multipurpose sanctuary as a home office, guest quarters, a retreat for teenagers, au pair accommodations, and more. 

    The granny flat has become a star in Australia’s huge housing landscape. Depending on size and style, a granny flat construction costs between $80,000 and $160,000.

    What is a granny flat?

    a small granny flat in the backyard

    Traditionally used as a place for elderly family members, a granny flat is a separate living area typically on the same land as the main house. Granny flats, as opposed to home additions or renovations, are separate buildings that provide solitude and function without major disruptions to the existing home.

    It can be a perfect bolthole for anyone who needs a break from the main house. Notably, in some Australian states, these granny flats can even be rented out, giving an additional source of income.

    What is the average cost to build a granny flat in Australia? 

    The average granny flat cost can vary depending on several factors. DIY or pre-fabricated options could be more budget-friendly, with average costs ranging from $10,000 to $30,000 for a basic model, $50,000 to $150,000 for a pre-fabricated design, and upwards to $250,000 for larger flat sizes.

    For custom-built granny flats, the average costs are categorised into low-range (around $1,000 to $1,500 per square metre), mid-range (approximately $1,500 to $2,500 per square metre), and high-range (starting from $2,500 per square metre).

    Cost of building a granny flat based on location

    The cost of building a granny flat is influenced by its location. Here’s a quick rundown of the average expenses in major Australian cities:

    City Average costs
    Sydney $10,000–$200,000
    Melbourne $10,000–$200,000
    Brisbane $25,000–$250,000
    Canberra $10,000–$200,000
    Perth $25,000–$150,000
    Darwin $25,000–$150,000
    Hobart $25,000–$150,000
    Adelaide $25,000–$250,000

    Granny flat building costs per type

    The type of structure you use can change the granny flat cost breakdown dramatically.

    Types of granny flats Average Reported Costs
    Attached $20,000
    Detached $25,000–$45,000
    Conversion $8,000–$10,000
    Custom-built $30,000–$200,000
    Flat packs $25,000
    Kits $10,000–$50,000
    Prefabricated $7,500–$25,000


    Some people prefer an attached granny flat because converting a garage to a granny flat costs much less than a fully detached one. An attached granny flat can cost thousands of dollars less than a detached one. An attached granny flat can cost about $20,000.


    A detached granny flat provides privacy and separation and can generate rental income. The $25,000 to $45,000 spent to construct the granny flat can be quickly recouped, and the granny flat can make a profit for years to come.


    Converting a garage into a granny flat is easier and less expensive than building a granny flat from the ground up. The required conversion reports and certificates cost about $8,000. The conversion can be done for under $10,000.


    Custom-built granny flats plans and prices can range from $30,000 to well over $200,000 when they have quality finishes and fittings.

    Flat packs

    The fabrication and procurement of flat pack granny flat materials can reduce the cost of a 20 square metre, one bedroom, granny flat price to as little as $25,000.


    Easy-to-use granny flats kits can cost as little as $10,000. The kits come with all the materials needed to construct a 45 to 60-square-metre granny flat for between $35,000 and $50,000.


    Prefabricated granny flats have sections manufactured in advance and off-site, shipped to the site and quickly and easily assembled. Prefabricated granny flats cost about $7,500 to $25,000.

    Granny flat prices based on the number of bedrooms

    Granny flat prices can vary depending on the number of bedrooms as well as amenities and fittings. 

    Number of bedrooms Average Reported Costs
    One-bedroom $10,000–$25,000
    Two-bedroom $30,000–$200,000
    Three-bedroom $55,000–$250,000

    One-bedroom granny flat

    These standard one-bedroom granny flats cost between $10,000 and $25,000. This is ideal for visiting family members, as it provides a living space for the grandparents or a warm and welcoming guest house.

    Two-bedroom granny flat

    Two-bedroom granny flat prices vary among builders, but they typically start at a reasonable range of about $30,000 to $150,000. Opting for a two-bedroom granny flat introduces a comfortable and convenient living space should the grandparents need a separate bedroom. 

    Three-bedroom granny flat

    On average, the total cost of a three-bedroom granny flat ranges between $55,000 and $250,000. It’s important to remember that even with a three-bedroom granny flat, you’re still limited to the regulatory maximum secondary housing lot size of 60 square metres. This demands changes, most commonly a reduction in the kitchen and living room area to accommodate the third bedroom.

    Granny flat prices based on sizes

    The price of a granny flat is related to its size. A small one can cost under $10,000.

    Size Average Reported Costs
    40 square metres $40,000–$85,000
    50 square metres $40,000–$100,000
    60 square metres $50,000–$125,000

    Factors affecting the costs of building a granny flat in Australia

    newly constructed granny flat


    The geographical setting plays a significant role in determining granny flat building costs. Urban areas often incur higher expenses than rural locations due to increased demand, accessibility, and regulatory considerations specific to each region.

    Local labour costs

    The availability and cost of skilled labour in the specific location can impact construction expenses. Areas with higher demand for construction services may experience increased labour costs. Moreover, you’ll need to consider the number of labourers and the duration of the construction project. 

    Accessibility and site conditions

    Challenges related to the site, such as difficult terrain or limited access, can affect construction costs. Specialised equipment or additional labour may be required to address unique site conditions.

    Flat size and number of rooms

    The size and number of rooms affect costs due to increased complexity in structural elements, plumbing, electrical systems, and overall square footage.

    Design complexity

    Intricate architectural designs or unconventional layouts contribute to higher building costs. The complexity may involve custom features, non-standard shapes, or unique structural requirements that demand specialised construction techniques and materials.

    Material choices

    While the choice of materials greatly influences the aesthetic and longevity of the granny flat, material types, such as premium finishes versus standard options, impact costs. The use of high-quality, durable materials incurs higher expenses.

    Energy efficiency considerations

    Incorporating energy-efficient features, such as solar panels, energy-efficient windows, or advanced insulation, can initially raise costs but may result in long-term savings and environmental benefits.

    Other building costs

    Beyond the construction, various ancillary expenses significantly contribute to the overall cost. This encompasses permits, council fees, site preparation, and inspection fees. Each element in this breakdown incurs its own set of costs that can vary based on location and regulatory requirements.

    Additional features

    Opting for luxurious fixtures, high-end interior finishes, and upscale amenities increases the overall cost. From top-tier flooring materials to premium cabinetry and high-quality appliances, these choices contribute to the final price tag. 

    Landscaping and outdoor amenities can influence granny flat costs as well. The need for extensive site preparation, retaining walls, or additional outdoor spaces will add to the overall budget.

    Granny flat building requirements

    New South Wales has legislation concerning the size of a property for a granny flat to be built. It is called the Affordable Housing State Environment Planning Policy. The law states that properties:

    • Larger than 450 square metres
    • Having a maximum external area of 60 square metres
    • A street frontage of 12 metres or more can have a granny flat built on it.

    Remember, construction or building rules might have local nuances, so checking with your local council is advised.

    For the most current information, visit official state government planning departments, local council websites, or trusted building authorities.

    How to hire a granny flat builder

    When hiring a builder for your granny flat project, making informed decisions can significantly impact the outcome. Here are tips to guide you through the selection process:

    Seek recommendations
    Ask for recommendations from family and friends who have had positive experiences with builders. Personal references can provide valuable insights into the builder’s work ethic, reliability, and overall satisfaction.

    Consult professional associations
    Contact your local council or homeowners association to access a pool of qualified and reputable builders. These associations often have stringent membership criteria, ensuring professionalism and adherence to industry standards.

    Conduct online research
    Leverage online resources to research potential builders. Check for customer reviews, testimonials, and examples of completed projects. Online platforms can offer a broader perspective on a builder’s reputation and capabilities.

    Evaluate pricing
    Look at what family, friends, and neighbours paid for similar projects. This benchmark can help you assess the fairness of quotes provided by potential builders.

    Get multiple quotes
    Contact at least three reputable builders and request detailed quotes. Comparing these quotes not only gives you a sense of the market rate but also helps in identifying any discrepancies or potential areas of negotiation.

    Verify licensing and qualifications
    Ensure the builder is licensed, bonded, and insured. A licensed builder signifies compliance with local regulations, while bonding and insurance protect you from potential liabilities. Additionally, verify that employees hold relevant professional certifications.

    Seamless living with your new granny flat

    Starting your granny flat journey opens up a world of possibilities, from cozy one-bedroom getaways to enormous three-bedroom havens. Hiring pros for your granny flat project ensures a seamless, high-quality result. 

    Navigate the possibilities with skill and make wise decisions when designing your granny flat hideaway. Your adventure into the world of adaptable and cost-effective living begins here, where friendly expertise meets your unique vision!

    FAQs on granny flats

    Is it possible to convert a garage into a granny flat? How much would it cost?

    The price of converting a garage into a granny flat can range from $25,000 to over $100,000. That includes report and certificate fees of $8,000 in addition to construction costs.

    How long does it take to construct a granny flat?

    Building the average granny flat can take about 8 to 12 weeks. Flatpack granny flat installation can take four to eight weeks. Granny flat kits can also be assembled quickly. There are also cyclone-proof, NBN-ready, five-star energy-rated, prefabricated granny flats that can be assembled in one day. However, you must ensure they comply with Australian construction standards.

    Is it worth building a granny flat?

    Yes. Aside from its functional purpose, they also increase the value of an existing property. This also boosts rental income and increases the sale price later. Granny flats are incredibly cost-effective when compared to purchasing an investment property.


    * The cost data is based on Oneflare and third-party sources

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