Is a granny flat worth building or fixing before you sell in Frankston? What it adds and what it does not
If the flat is already there and legal, spend $3,000 to $12,000 tidying it and you will get that back. If it is there and unapproved, that is the single biggest price killer on a Frankston sale, and fixing the paperwork costs $4,500 to $18,000 against a discount of $40,000 to $100,000. If it is not there at all, do not build one to sell: a $150,000 two-bedroom build typically adds $90,000 to $160,000 to the price and takes six to nine months you probably do not have. Build it to use, not to flip.
What each job costs, what it realistically returns, and a straight verdict
The verdict column is what we would tell a family member. Costs are 2026 Frankston and Mornington Peninsula figures for a 35 to 60 square metre second dwelling. Return figures are what we see reflected in negotiation and in valuations, not a promise.
| The job | What it costs | What it adds or protects at sale | Verdict |
|---|---|---|---|
| Retrospective building approval for an unapproved granny flat | $4,500 to $18,000 | Removes a $40,000 to $100,000 discount and keeps the flat inside the lender valuation | Do it |
| Assemble the permit, occupancy permit, plans and warranties into one folder | $0 to $1,200 | Stops the conveyancing delay and the late price chip. Buyers pay for certainty | Do it |
| Fix damp, mould and the drainage causing it | $2,800 to $7,500 | A damp or mould note in a building report costs $20,000 to $50,000 in negotiation | Do it |
| Repaint the interior in a neutral, clean up the wet areas, re-silicone | $1,800 to $4,200 | Photographs as a second dwelling instead of a shed. Usually returns two to three times the spend | Do it |
| Written rental appraisal for the flat from a local agent | $0 | Lets the agent advertise a real yield, which is what brings investors to the open | Do it |
| Replace worn or lifting floor covering | $2,700 to $5,400 | Modest, but stained or lifting floors read as needs work and invite a low offer | Only if the existing is stained, lifting or smells |
| Separate electricity meter for the granny flat | $1,800 to $4,500 | Matters to investor buyers, invisible to owner-occupiers | Only if the agent is targeting investors |
| Tidy the surrounds: mulch, edging, pressure wash, prune | $600 to $1,400 | Best dollar-for-dollar spend on the whole property for photography | Do it |
| New kitchen in the granny flat | $12,000 to $28,000 | Rarely returns the spend. Buyers price a second dwelling on legality and rentability | Skip it |
| Stone benchtops and premium tapware | $4,000 to $9,000 | No measurable effect on the granny flat component of the price | Skip it |
| Full landscaping scheme around the flat | $8,000 to $20,000 | The $900 tidy-up version captures most of the visual benefit | Skip it |
| Building a brand new granny flat purely to sell | $95,000 to $220,000 | Adds $90,000 to $160,000 and takes 6 to 9 months including approvals | Skip it unless you were building anyway |
| Converting the garage to a flat without a permit before the sale | $18,000 to $45,000 | Reduces value, creates disclosure liability and can trigger council enforcement | Skip it |
Indicative 2026 Frankston and Peninsula figures. Your agent knows your street better than any table: use both.
What buyers and building inspectors actually notice
A buyer walks from the back door to the granny flat door in about fifteen seconds and forms most of their opinion in that walk. What lands: whether the path is a proper path or a line of pavers on dirt, whether the flat looks like a designed dwelling or a shed with a window, whether the door opens without dragging, whether it smells musty, and whether there is obvious separation from the main house. Almost nobody opens a cupboard. Almost everybody sniffs.
The building inspector is different, and far more expensive to get wrong. A pre-purchase inspection carried out to the Australian standard for pre-purchase inspections covers structure, dampness, timber pest activity and safety, and the granny flat is inspected as part of the property. In Frankston, Langwarrin and Skye the findings that come up over and over are movement cracking from reactive clay soils, damp along the slab edge where garden beds have been built up over the top of it, mould in the bathroom corner of a small tightly-sealed dwelling, ponding water under a flat on stumps, and a shower that leaks into the wall frame. Closer to the bay in Seaford, Frankston beachfront and Mt Martha, add corroding fixings, rusted flashings and perished seals from salt air.
Two findings cost more than the rest combined. The first is timber pest activity: any mention of live termites turns a negotiation into a demolition discussion. The second is anything that reads as unlawful building work, because the buyer cannot price the risk and their conveyancer will tell them to assume the worst. Our maintenance schedule covers the inspection and drainage jobs that prevent most of these, and the drainage page covers the fix when damp is already there.
The section 32 trap, and fix versus disclose
Victoria puts a real disclosure obligation on the seller. The vendor statement, commonly called the section 32, must include particulars of building permits issued for residential building work on the land in the preceding seven years, along with notices, orders and approvals affecting the land. If you built the flat as an owner-builder and you sell within the statutory period after completion, you also have to provide a defects inspection report and the required domestic building insurance. A conveyancer will ask you directly whether the granny flat is approved, and the answer goes on the record.
That turns the fix-versus-disclose question into a fairly simple decision. Disclosing an unapproved structure does not make it safe to sell: the buyer prices in the worst case, the lender may exclude the flat from the valuation, and some buyers walk. Fixing it costs $4,500 to $18,000 in reports, plans, an engineer, a building surveyor and any rectification work the surveyor requires, and takes eight to twenty weeks. Against a discount of $40,000 to $100,000, that is the easiest decision on this page. Start it four to six months before you list, because you cannot compress a building surveyor.
For everything else, the rule is: fix what a report will call a defect, disclose what a report will call a characteristic. A hairline shrinkage crack in a slab is a characteristic. Movement cracking wide enough to put a coin in is a defect. Rust on a fence is a characteristic. Rust through a roof sheet is a defect. If it is a defect and it is under about $8,000, fix it, because a buyer will price the same item at three to five times the trade cost.
Timing: how long before the campaign
- Retrospective approval: 3 to 5 months. Start first, before anything else.
- Drainage or damp rectification: 6 to 8 weeks, because the wall has to dry before it can be repainted properly. Painting over a damp wall is visible in photos and obvious to an inspector.
- Interior repaint: 2 weeks before photography, so it can cure and stop smelling of paint.
- Cosmetic tidy, mulch, pressure wash, prune: 3 to 4 weeks out, then a light touch-up the week of the first open.
- A new granny flat build: 6 to 9 months including approvals. See the best time to build page and the build process for the real sequence.
Selling in the next six months?
We will walk the property, tell you what a building inspector will write, and price only the work that is worth doing.
Two jobs we would honestly tell you not to bother with
One: a new kitchen in the granny flat. At $12,000 to $28,000 this feels like it should move the price, and it does not. A buyer values a second dwelling on three things: is it legal, is it dry, and what does it rent for. A new kitchen changes none of them. If the existing kitchen works, clean it, replace the handles for $180, re-silicone the splashback and spend the rest on the paperwork.
Two: a full landscaping scheme around the flat. At $8,000 to $20,000 this is the classic pre-sale over-spend. Photographs reward tidiness, not design. Mulch, edging, a pressure-washed path, a pruned hedge and a $60 pot by the door do about 80 per cent of what a designed garden does in a listing photo, for around $900. Put the difference into drainage, which is invisible in photos and decisive in the building report.
A third one worth naming: solar and battery purely for the sale. It is a $8,500 to $18,500 spend that buyers appreciate but do not pay a premium for, and it is a genuinely good investment only if you are staying long enough to use it.
What we do not do
We are builders, not agents or valuers. We will not tell you what your house is worth, and we will not quote a job we do not think you should do. If you call us about a pre-sale granny flat build and you are listing in four months, we will tell you it cannot be done in time rather than take a deposit. If your flat needs $3,000 of work and an agent has told you it needs $40,000, we will put that in writing for you. Our quote comparison guide explains how to read anybody else's number, and the pricing page has the 2026 ranges for the work itself.
Get a pre-sale scope that only prices the work worth doing
Send the details and we will walk the property and email a prioritised, fixed-price list within 7 days, with the skip-it items marked as skip it.
Questions sellers ask
Does a granny flat add value to a house in Frankston?
What happens if my granny flat has no building permit when I sell?
What does a pre-purchase building inspection pick up on a granny flat?
Do I have to disclose the granny flat in the section 32?
How long before the campaign should the work be finished?
What should I not bother spending money on before selling?
Related: Victorian permit rules, renting it out instead of selling, insurance and claims, and what site costs really run to.