⚠️ The truth: Most homeowners spend 15–25% more than their builder’s quote. On a $600K build, that’s $90K–$150K in “extras” you didn’t budget for.
Your builder hands you a quote for $600,000. You nod, sign the contract, and think that’s the number. It won’t be. Not even close. These are the 15 costs that land outside that quote, and what you should actually be budgeting.
The 15 Hidden Costs
1. Site Costs ($10,000 – $60,000+)
Every builder’s quote has a line item called “site costs allowance,” usually somewhere between $15K and $25K. Sounds generous until you find out your block is sitting on reactive clay or has a 2-metre fall across the rear. Actual site costs regularly blow past the allowance by 2-3x. Always get a soil test before signing a contract. The $1,000 you spend on that test could save you $30,000 in surprises.
2. Landscaping ($10,000 – $80,000+)
On handover day, you get a house surrounded by a sea of mud. Turf, garden beds, paths, retaining walls, irrigation, outdoor lighting? All on you. People lie to themselves about this one. Budget $15K–$30K minimum for a basic front and back yard, and that’s before anyone mentions a deck or pergola.
3. Fencing ($5,000 – $20,000)
Check your contract carefully. Most include one side of boundary fencing, and some include none at all. A full Colorbond fence around a standard 500sqm block runs $8K–$15K. Go timber and you’re paying more again.
4. Driveway and Crossover ($3,000 – $15,000)
Your builder probably includes the driveway from the garage to your property boundary. The crossover, though, which is the section from the boundary to the road? Usually excluded. And council has opinions about crossover specs, so you can’t just pour whatever you like.
5. Blinds and Curtains ($3,000 – $15,000)
Almost never included. You move in and every window is bare. Roller blinds for a 4-bedroom home start around $3K. Plantation shutters or motorised blinds? You’re looking at $15K+. It’s one of those costs that feels small until you count the windows.
6. Air Conditioning ($5,000 – $20,000)
Read the fine print. Some builders include ducted heating but not cooling. Others throw in split systems for the bedrooms and call it done. If you want full ducted reverse-cycle through a 250sqm home, that’s $10K–$18K out of your own pocket.
7. Connection Fees ($5,000 – $15,000)
Water, gas, electricity, NBN. Each one has a separate fee, a separate application, and takes its own sweet time. Sewer alone can run $3K–$8K depending on how far you are from the main. Not glamorous. Still needs paying for.
8. Council Permits ($5,000 – $15,000)
Planning permit (if you need one): $1K–$5K. Building permit: $2K–$5K. Then there are inspection fees, bond fees, and in some council areas, a “damage deposit” because the trucks chew up the nature strip. It adds up.
See your real build cost — including the extras
Our calculator accounts for site costs, connections, and the hidden extras most estimates miss.
9. Architect/Designer Fees ($15,000 – $60,000)
Going custom? An architect or building designer charges 3–8% of the build cost. On a $600K build, that’s $18K–$48K before a single brick is laid. Volume builder plans dodge this cost, but you get a house that looks like every third one on the street.
10. Soil Test and Survey ($2,000 – $5,000)
You can’t skip these. Soil test: $500–$1,500. Feature and level survey: $500–$1,500. Engineering assessment: $500–$2,000. They’re not optional, and the builder won’t start without them.
11. Upgraded Inclusions ($10,000 – $50,000+)
This gets everyone. Your builder’s “standard inclusions” mean laminate benchtops, basic tapware, and builder-grade tiles. You walk through the display home and fall in love with the stone benchtops, the matte black fixtures, the herringbone splashback. That’s all upgrade pricing. And once you start upgrading one thing, you end up upgrading everything because the standard stuff looks cheap next to it.
12. Window Furnishings ($1,000 – $5,000)
Flyscreens, security screens, window tinting. Builders leave these out more often than you’d think. Security screens alone can run a couple of thousand for a full house.
13. Letterbox, Clothesline, TV Antenna ($500 – $2,000)
Individually small. Collectively annoying. Your builder might throw in a letterbox but forget the clothesline and TV antenna point. You don’t notice these are missing until you’re standing in your new house with a basket of wet laundry and nowhere to hang it.
14. Temporary Accommodation ($15,000 – $40,000)
Doing a knockdown rebuild? You need somewhere to live while your old house becomes your new house. That’s 10–22 months of rent. At $400/week, you’re looking at $17K–$36K, and that’s before you factor in storage for your furniture.
15. Interest During Construction ($10,000 – $25,000)
Nobody thinks about this one. If you have a construction loan, you’re paying interest on every progressive drawdown during the 12–18 month build. That interest adds up to $10K–$25K, and somehow it never makes it into anyone’s spreadsheet until after the fact.
Total Hidden Costs: What to Actually Budget
| Category | Minimum | Typical | Maximum |
|---|---|---|---|
| Site costs (above allowance) | $0 | $15,000 | $40,000+ |
| Landscaping | $10,000 | $25,000 | $80,000+ |
| Fencing | $5,000 | $10,000 | $20,000 |
| Driveway/crossover | $3,000 | $6,000 | $15,000 |
| Blinds | $3,000 | $6,000 | $15,000 |
| A/C (if not included) | $5,000 | $12,000 | $20,000 |
| Connections | $5,000 | $8,000 | $15,000 |
| Permits | $3,000 | $7,000 | $15,000 |
| Upgraded inclusions | $0 | $15,000 | $50,000+ |
| Other (letterbox, screens, etc.) | $1,000 | $3,000 | $5,000 |
| Total hidden costs | $35,000 | $107,000 | $275,000+ |
The real number: Add 20–25% to your builder’s quote for the true move-in-ready cost. On a $600K build, budget $720K–$750K total.
Upgraded inclusions add $10K–$50K+
The display home finishes aren't the standard ones
How to Protect Yourself
- Get a fixed-price contract with a detailed inclusions list
- Get a soil test before signing — don’t rely on the builder’s site cost “allowance”
- Ask for the upgrade price list upfront — know what the display home extras cost
- Budget separately for landscaping, fencing, blinds, and connections
- Include a 10% contingency beyond the hidden costs
- Read the contract exclusions page — this is where the hidden costs live
Frequently Asked Questions
How much should I budget on top of my builder’s quote?
Roughly 20–25% on top of whatever the builder quoted. That covers site costs, landscaping, fencing, connections, permits, blinds, and the upgraded inclusions you’ll inevitably want. So a $600,000 build? Budget $720,000–$750,000 to actually move in and live there. Got slope, rock, or reactive clay on your block? Budget even more for site works.
Are hidden costs included in a fixed-price building contract?
Short answer: no. A fixed-price contract locks in the build itself, but landscaping, fencing, blinds, driveway crossovers, A/C upgrades, and utility connections are almost always excluded. Flip to the “exclusions” section of your contract. That page is where the real costs are hiding. Before you sign anything, ask for a full inclusions schedule and read it line by line.
What is the biggest hidden cost when building a home?
Site costs, hands down. They can blow out by $10,000 to $60,000+ above what your builder allowed for. Reactive clay soil, which is everywhere in Melbourne’s west, means deeper footings, retaining walls, and more earthworks than anyone expected. Sloping blocks are just as bad. Get an independent soil test before signing. Cheapest insurance you’ll ever buy against a budget blowout.
Can I reduce hidden costs by choosing a volume builder?
You can, but there’s a trade-off. Volume builders have lower base prices because their standard inclusions are budget-grade. Walk through the display home, fall in love with it, then find out those finishes cost $15,000–$50,000 extra. A custom builder might quote higher upfront but actually include the things you want. The only number that matters is the total move-in cost. Compare that, not the contract price.
Costs based on Q1 2026 Australian market data.
Related Guides
- Cost to Build in Melbourne — Full cost breakdown
- Cost to Build in Sydney — Sydney costs
- Build vs Buy — Compare the true costs
- Construction Loan vs Home Loan — Finance explained
