Why you don't get your renovation money back

A renovation adds value by winding back the effective age of the parts of the house you actually touch. That is the whole mechanism. It is also why a cosmetic refit cannot return a house to new — most of what a house costs to build is not cosmetic, and you are not renewing it.

The 63% you cannot renovate

Split the cost of rebuilding a house into 29 elements, each with its own working life — framing and slab run 70–90 years, a kitchen or a floor covering runs 15–18. Grouped, they read like this:

Group	Share of dwelling cost	Typical life
Structural core — slab, frame, roof structure	23.6%	70–90 yrs
Exterior envelope — facade, roof covering, windows, doors	22.8%	25–80 yrs
Wet areas — kitchen, bathroom, ensuite, laundry	18.1%	18–22 yrs
Services — plumbing, wiring, HVAC, hot water, appliances	16.2%	10–45 yrs
Interior finishes, by room — bedrooms, living, dining, hallway, study	13.7%	15–18 yrs
Interior linings — ceilings, internal doors	5.5%	35–45 yrs

26 components, grouped, as a share of what it costs to rebuild the DWELLING — each decays toward its own floor value on its own service life, not a straight line to zero. The garage, landscaping and driveway are real assets too, but they sit outside this figure entirely: they are priced and depreciated against their own replacement cost, not the house's.

A standard cosmetic renovation replaces the wet areas, refreshes the rest of the interior, and repaints the ceilings and swaps the internal doors while it is at it — kitchen, bathrooms, floors, paint, ceilings, doors. That reaches 37% of the dwelling's cost base: wet areas, interior finishes and interior linings together. The structural core, the envelope and the services — 63% — are exactly as old on the day you finish as they were on the day you started.

What nine and a half years is worth

Each component depreciates on its own curve, geometrically, toward a residual floor rather than to zero — a wiring circuit at the end of its 30-year life is written down further than a slab at the end of its 90-year one. Run the refit above — wet areas, interior finishes and linings — on a house whose envelope would cost $606,000 to rebuild today:

Spend $216,579 on that scope and you have created $175,194 of value. That is an 81% recovery — inside the 57–80% range everyone quotes, once ceilings and doors are added to the wet areas and finishes and priced at what that actually costs. The difference is that this number came from somewhere. Change the age, the scope or the build rate and it moves, in a direction you can predict.

It also shows you the lever. The recovery rate is not a property of kitchens. It is a property of how much effective age your scope actually resets, on a house of that age. Renovating a 40-year-old house recovers more than renovating a 10-year-old one, for identical work, because there is more age to buy back.

Why an underpriced scope does not buy the reset

Ticking “rewire the house” does not renew the wiring — spending what it costs to renew the wiring does. Where the money allocated to a component falls short of its share of replacement cost, the effective age only comes back proportionally. This is the arithmetic that stops a cheap scope producing a recovery rate above 100%, which is what naive percentage models cheerfully report.

The median fallacy

The most common mistake in a renovation feasibility is testing the finished value against the suburb median.

Half of all sales in a suburb are above the median. That is what a median is. A renovated house — by construction — belongs in the upper half. Testing it against the middle number tells you almost nothing, and it will talk you out of work that was fine.

The right ceiling is the distribution of renovated comparable sales for the finished configuration: the same bed and bath count, in that suburb, actually renovated. Then apply a hard stop near the top of that distribution rather than the middle of it. Pushing a finished property past what the best houses of its configuration achieve is the point where the last dollars stop coming back — and those last dollars are the ones you spend on the fittings you liked in the showroom.

What a lender will credit you with

If you are funding the work, your own view of the finished value is not the operative number. A lender sizes against an as-if-complete valuation, and a common conservative test credits only about 70% of what you spend as value created, taking the lower of that and the valuer's figure.

On the example above, a lender's 70% test credits $151,605 of the $216,579 spent — still under the $175,194 this model finds, though closer than it looks at a lighter scope. The two are independent measures and are not meant to agree: DRC prices the physical asset, and a lender's haircut exists precisely so a facility does not depend on one quantity surveyor's number being right for every project. When they diverge, the lender's figure is what the facility is sized against, not the model's.

GST, if you are selling

A renovation you keep has no GST consequence. A renovation you sell might, and the threshold is not about how much you spent.

GST bites on a sale where the work amounts to a substantial renovation — broadly, where most of the building has been removed or replaced, affecting the building as a whole, not just a cosmetic refresh of the rooms buyers look at. A new kitchen, new bathrooms and new floors is almost never substantial. Taking the house back to its frame usually is.

Where it applies, the margin scheme can reduce what is payable on the sale, which is why a project that fails on a full-GST assumption sometimes works under it. Input tax credits on the renovation spend are real, too — but they show up as a lower cost figure, not as a refund on top of what this calculator already treats as the cost of the work. The definition is the ATO's and it is fact-specific: this is the one input on the page worth taking to your accountant rather than settling from a calculator.