Planning a home renovation: budgeting before the walls come off

What the job involves

Renovation budgets are best sanity-checked per square metre of the space you're actually touching. Cosmetic work — paint, flooring, lighting, a joinery update — sits at the bottom of the range. A full internal renovation with a new kitchen and bathrooms in the existing footprint lands in the middle. Anything structural — moving or removing walls, extending — sits at the top.

The two biggest cost jumps are wet areas and walls. Kitchens and bathrooms concentrate plumbing, electrical and waterproofing into small spaces, so each one adds a dense block of trades and cost. Moving or removing a structural wall brings engineers, steel and council approval into the picture. Older homes add their own surprises — old wiring, dodgy plumbing, asbestos, out-of-level floors — that only appear once work starts.

A renovation is a coordinated build, not a single trade. A builder or project manager sequences the plumbers, electricians, plasterers, tilers and painters so the job flows, and that coordination is part of what you're paying for.

How the cost works

A cosmetic refresh across the main living areas sits at the bottom of the range, a full internal renovation with new wet areas lands in the middle, and a major structural reconfiguration or extension reaches the top. The estimate on this page adjusts for area, scope and finish level, so treat any figure as a starting envelope — every renovation is genuinely different.

The square metres you touch and how deeply you touch them set the baseline, but finish level swings the same layout dramatically: fixtures, joinery and material selections can move an identical floor plan by a large margin. The rule that saves the most grief is holding back a ten to twenty per cent contingency, because older homes almost always reveal something once they're opened up, and a budget with no slack turns every surprise into a crisis.

Choosing and verifying a builder

Residential building work over a threshold value requires a licensed builder in every state, though the threshold and licence class differ — so check your state's building authority and verify the builder's licence and ABN before signing. For contracts above a set value, home warranty (builder's warranty) insurance is also mandatory in most states, and it protects you if the builder can't finish; confirm it's in place for your contract value.

Beyond the paperwork, lock your selections — tiles, tapware, appliances — before the build starts, because late changes are the most expensive kind. Ask how variations are priced and documented, and choose a builder who gives you an itemised, staged quote rather than a single lump sum, so you can see what you're paying for and track it as the job runs.

Mistakes to avoid

Renovation regrets are usually about no contingency, late decisions, or skipped licence and insurance checks.

• Running with no contingency, so the first hidden surprise blows the budget
• Not verifying the builder's licence and home warranty insurance for the contract value
• Changing selections mid-build, when late changes cost the most
• Underestimating how much each kitchen and bathroom concentrates trades and cost
• Removing a wall without engineering and approval because it 'looked non-structural'
• Accepting a single lump-sum price instead of an itemised, staged quote you can track