The plan is always the same. Buy the tired one on the good street, spend a bit, end up with the house you could never have afforded finished.
It works often enough that people keep doing it. It also fails often enough that agents have a phrase for the ones who got it wrong, and the phrase is not kind.
The difference is rarely luck. It is whether the buyer understood what they were taking on before the hammer came down, or after.
Auction day gives you no cooling off period. Everything that matters has to happen in the two or three weeks before it.
Renovation potential is not the same as renovation permission
A house can be physically easy to extend and legally very hard.
Check the planning controls on the property before you fall for it. Zone, overlays, covenants on title, easements, setback requirements, and whether the street has a heritage listing. Melbourne is full of unremarkable weatherboards sitting inside a heritage overlay where the front two rooms are effectively untouchable.
A neighbourhood character overlay can rule out the second storey you were mentally already living in. A sewer easement down the side can make the extension footprint you assumed impossible without a build-over agreement.
None of this stops the project. All of it changes the cost, and it is knowable before you bid.
Look at the structure, not the finishes
Bad kitchens are cheap to fix. Bad footings are not.
The expensive problems in older Melbourne housing tend to be the ones you cannot see from the doorway. Stumps that have moved. Reactive clay soil doing what reactive clay soil does. Rising damp. Poor subfloor ventilation. Rot in the bearers. A roof structure that will not take the load of anything above it.
Signs worth noticing on an inspection walkthrough. Doors that will not close square. Cracking above windows and at corners. Floors that slope in one direction. Fresh paint on one wall only. A smell in the hallway that nobody mentions.
None of these are conclusive. All of them are worth asking about.
Assume the services need work
Older homes carry old wiring, old plumbing and old drainage, and renovation work tends to force the issue.
If you open a wall, the wiring in that wall generally has to come up to current standards. If you connect new plumbing to old clay drainage, you may find out the hard way what condition the old drainage is in. Switchboards without safety switches need upgrading. Some houses still have rubber-insulated wiring, and no electrician is going to leave that alone.
These are not disasters. They are just costs that people budget zero for, because a light switch looks the same whether the wiring behind it is from 1960 or last year.
Ask about asbestos and lead early
Anything built or renovated before the late 1980s in Australia may contain asbestos. Eaves, sheeting, backing to wet areas, vinyl underlay, fencing. Pre-1970s paint may contain lead.
Neither is a reason to walk away. Both are a reason to budget properly, because removal is licensed work with disposal costs, and finding it mid-demolition stops the job while you organise it.
Work out the access problem
Access does not show up in a building report and it changes the price of everything.
Can a truck get in. Is there anywhere to put a skip. Can a concrete pump reach the back. Do materials have to be carried through the house or craned over it. Is there room to store anything on site, or does every delivery have to be same-day.
A tight inner-city site with no rear access can add a meaningful percentage to a build for no visible reason at all. Builders price it. Buyers rarely do.
Get independent advice before the auction, not after
Standard building and pest inspections tell you the condition of what is there. They are worth getting and they are not the same as advice about what you want to do with it.
Bringing in a building consultant Melbourne buyers can engage before they bid closes a different gap. Instead of a list of defects, you get a read on buildability. Whether the extension you have in mind is realistic on that block. Which permit path it is likely to need. What the visible defects mean for a renovation rather than for living in it as is. Which costs you have not thought of.
That advice is a few hundred dollars against a bid worth a million or more. If it changes your ceiling by even a small margin, or stops you buying the wrong house entirely, the arithmetic is not close.
Cost the renovation before you set the limit
The common failure is bidding to a number that assumed a renovation cost pulled from a television show.
Do it properly. Get a rough build cost per square metre from someone who builds in that area. Add design and documentation, permit fees, consultant fees, connections, landscaping reinstatement, and a contingency of at least fifteen percent for a house whose insides you have not seen.
Then check the finished value against comparable sales on the street, because there is a ceiling on what any street will pay, and overcapitalising on a renovation is easier than it sounds.
If purchase plus renovation exceeds what a finished house nearby sells for, the deal only works if you plan to stay a long time. Some people do. Just make it a decision rather than a discovery.
Set the limit before you go, and write it down
Auctions are designed to make you spend more than you meant to. Standing in a crowd on a Saturday morning with an agent working the room is not the moment to be doing sums.
Do the sums during the week. Write the number on your hand if you have to. Have someone with you whose job is to stop you.
The houses that turn into cautionary tales are almost never the ones with the worst structural problems. They are the ones bought thirty thousand over the limit by someone who had run out of weekends and just wanted it to be over.
Spend the money on advice before the auction. It is the cheapest part of the whole exercise and the only part where a few hundred dollars can change the outcome by six figures.