Last updated October 2026
A granny flat for adult children gives your grown kids their own front door, kitchen and bathroom in your backyard, while keeping the family close. For many Melbourne families it sits between two options that no longer feel right: sharing the family home well into your child’s twenties, or watching them move into a rental across town. This guide covers why families build, how to design for independence, the agreements worth making early, the costs and the approvals involved.
This guide is general information only and is not tax, legal or financial advice. Speak with a registered tax agent and a licensed finance professional about your situation.
Key takeaways
- A granny flat for adult children gives everyone their own space on the one block.
- Design for independence with a separate entry, a full kitchen and privacy between the two homes.
- Agree on rent, bills, visitors and timeframes in writing before your child moves in.
- A turnkey G-Flat™ costs $198,000 to $265,000, depending on the finish level.
- Most Melbourne residential zones need no planning permit for a granny flat of 60m² or less, but a building permit is required.
Why families build a granny flat for adult children
Adult children are living at home for longer, and the reasons are familiar: study, starting a career, saving for a home of their own, or simply wanting to stay near family. Sharing one roof can work for a while, but it often gets harder as everyone’s routines and needs change.
Families usually build a granny flat for adult children to:
- give their child a genuine sense of independence without moving away
- get their own home, space and routines back
- help their child save while they build a career or a deposit
- keep support close at hand, whether that is a shared dinner or help with a flat tyre
- create a space that can house other family members later
It is not about making life easy for your kids. It is about giving them room to run their own household, with family a few steps away. Our article on kids who can’t move out looks at this shift in more detail.
Is it the right move for your family?
A backyard home suits some families better than others. It tends to work well when:
- your relationship with your adult child is generally good
- your child has a plan, such as saving, studying or settling into work
- everyone agrees on how the arrangement will work and roughly how long it will last
- your block has the space and access for a second dwelling
It may not be the answer if relationships are already strained, if your child needs some distance to stand on their own feet, or if your block is too small or heavily constrained. A frank family conversation is the first step, well before anyone looks at floor plans.
If your child is still in their late teens, can a granny flat be your teen’s first home? covers that earlier stage.
Designing a granny flat for adult children
Designing for a 25 year old is different from designing for an ageing parent. Young adults want a home that feels like theirs, not a spare room at the end of the garden. Good design is what makes the arrangement feel like independence rather than supervision.
A separate entry and clear sight lines
Your child should be able to come and go without walking through your home or past your living room windows. When you position the granny flat on the block, think about:
- which way the front door faces
- which windows look towards the main house
- a separate path from the street or side gate
- outdoor space that belongs to the granny flat, such as a deck or landing
A full kitchen and bathroom
In Victoria, a small second dwelling must include a kitchen, bathroom and toilet, so your child has everything needed to run their own household. Every G-Flat™ includes stone benchtops, soft-close cabinetry, SPC hybrid flooring and a reverse cycle split system, so the home is comfortable from day one.
Two bedrooms that adapt
Every G-Flat™ is a 60m², two bedroom home. For an adult child, the second bedroom earns its keep as:
- a home office for work from home days
- a study for university or TAFE
- a guest room for friends or a partner
- storage for hobbies, sports gear or a bike
Choosing a floor plan
All five G-Flat™ floor plans cost the same within each finish level, so you can choose the layout that suits your block and your child:
- Stella: an L-shaped plan for corner or irregular blocks
- Aurora: long and narrow for tight or side-access blocks, with a walk-in robe in bedroom one
- Lana: a balanced layout that fits most backyards
- Lana 2: adds a second bathroom, handy if your child shares with a friend or partner
- Sirius: a square plan with large 4 x 3m bedrooms and an L-shaped kitchen
See 2 bedroom granny flat designs and every G-Flat™ layout and finish explained for more on each plan.
Privacy and sound
Small details make a big difference to how both homes feel:
- leave space between the two buildings where your block allows
- avoid bedroom windows that face straight onto your outdoor living area
- use screening or planting to soften sight lines (landscaping is arranged separately)
- double-glazed windows, included in every G-Flat™, help reduce outside noise
House rules and family agreements
A granny flat solves the space problem. Clear agreements solve the relationship problem. Have these conversations before construction starts, while everyone is excited and open, rather than after a disagreement.
Money
Decide whether your child will pay rent, contribute to bills, or live there while saving towards a goal. Whatever you choose, write it down. If they pay rent, agree on the amount, how often it is paid and when it will be reviewed.
If your child pays rent, Victorian rental laws may apply to the arrangement, so check your obligations with Consumer Affairs Victoria. Our guide on how to legally rent out a granny flat in Victoria explains the basics.
Bills and utilities
Agree up front how electricity, water and internet will be shared. Some families split bills by an agreed share, while others install a separate electricity meter. See how to split utility bills and our guide to a separate electricity meter for a granny flat.
Privacy both ways
Set a few simple ground rules:
- knock or message before visiting, in both directions
- agree on how shared areas such as the driveway, bins and clothesline are used
- talk about partners staying over and friends visiting
- agree on reasonable quiet hours
Responsibilities
Agree who looks after cleaning, the granny flat’s outdoor area, minor repairs and reporting maintenance issues. Treating the granny flat as your child’s home, with their own responsibilities, helps them build the habits they will need when they move out.
Timeframes and reviews
Agree on a rough timeframe, such as two or three years or until a savings goal is reached, and set a date to check in. A regular review keeps the arrangement working for everyone and stops it drifting without a plan.
Granny flat for adult children: costs and finance
Every G-Flat™ is a turnkey build with a fixed price for each finish level:
| Finish level | Turnkey price |
|---|---|
| Affordable | $198,000 |
| Homestead | $208,000 |
| Signature | $238,000 |
| Luxe | $265,000 |
Prices are a guide only and depend on your site. Sites 70km or more from the Melbourne CBD attract a 12.5% regional surcharge. A free site assessment confirms the price for your block.
Each price includes the building permit and required reports, all plans, connection of services up to 10m from the main house and a 10-year structural warranty. Our guide to granny flat inclusions in Melbourne lists what comes with each finish level.
Paying for the build
Families commonly fund a granny flat through savings, equity in the family home or a construction loan. A licensed mortgage broker can explain which options suit your circumstances, and our guide on how to finance a granny flat build covers the main approaches.
Some families also agree that their adult child will contribute to the cost. If you go down this path, put the arrangement in writing and have each party get independent advice.
Tax questions to ask
Tax treatment depends on how the granny flat is used and whether rent is charged at market rates. Charging your child rent, renting to a tenant later, or treating the granny flat as part of your home can each lead to different outcomes, including for capital gains tax on your main residence. Speak with a registered tax agent before you build, and see the ATO website for general guidance.
Approvals for a granny flat for adult children
In Victoria, a granny flat is known as a small second dwelling. The key rules are:
- the floor area must be 60m² or less
- it must include a kitchen, bathroom and toilet
- it must be on the same lot as an existing home
- no planning permit is needed in most residential zones, although lots under 300m² and some overlays (such as heritage, bushfire or flood) may need one
- a building permit is required
- it cannot be subdivided or sold separately from the main home
- it cannot be connected to reticulated gas
- no extra car park is required
The Victorian Government small second dwellings page sets out the official rules, and our guide to granny flat approvals in Victoria explains the process.
Easements, covenants and trees can also affect where a granny flat can go, so your free site assessment checks these early. See what makes a block suitable for a granny flat for what we look at.
A G-Flat™ takes approximately 5 months end to end, from planning through to handover, including the building permit, approvals, construction and connection of services.
A home that adapts as your family changes
A granny flat for adult children does not have to stay that way. Family needs change over the years, and a self-contained 60m² home can change with them:
- a younger sibling may need the same start a few years later
- ageing parents may move in to be closer to family
- you may choose to downsize into it yourselves one day
- you may decide to rent it out, in which case residential tenancy laws apply
If renting becomes part of your plan, rents vary by suburb, finish and demand, and a local property manager can give you a rental appraisal. Our article on two families on one block explores these options.
Frequently asked questions
Do I need a planning permit for a granny flat for adult children?
In most Melbourne residential zones, no planning permit is needed for a small second dwelling of 60m² or less. Lots under 300m² and some overlays may need one, and a building permit is required.
Can my adult child pay me rent?
Yes, but rent can have tax and legal implications. Put the arrangement in writing and check your obligations with a registered tax agent and Consumer Affairs Victoria.
Can I sell the granny flat to my child separately?
No. A small second dwelling in Victoria cannot be subdivided or sold separately from the main home.
How long does it take to build?
A G-Flat™ takes approximately 5 months end to end, from planning through to handover.
Which floor plan suits an adult child?
Start with the plan that suits your block. Lana 2 adds a second bathroom, which works well for a child sharing with a partner or friend.
Plan a granny flat for adult children with confidence
The right granny flat for adult children starts with your block and an honest family conversation. Book your free site assessment or visit our display G-Flat™.