Guide
Fixed price or charge-up: what each one actually risks
This is not a pricing preference. It is a decision about who carries the cost of what nobody can see yet — and on a renovation, unlike a new build, there is always something nobody can see yet.
$163,752
Average declared value of an Auckland dwelling alteration consent in the year to May 2026 — $712.32m over 4,350 consents. Declared value is what was estimated at consent time. It is not what the work finally cost, and the gap between those two numbers is the subject of this page.
Stats NZ — Building consents issued — Auckland local boards, May 2026 release · May 2026
The trade
The same job, priced two ways
| Fixed price (lump sum) | Charge-up (cost plus) | |
|---|---|---|
| Who carries the unknowns | The builder | You |
| What you pay for that | A risk premium inside the price | Nothing — you keep the risk |
| Certainty of the final number | High, until a variation | Low until the job finishes |
| Incentive on efficiency | On the builder — they keep the saving | On nobody in particular |
| Where disputes come from | What was in the scope | What the hours were spent on |
| Honest when | Scope is defined and the building is known | Scope genuinely cannot be defined yet |
| Dishonest when | A tight number is quoted knowing variations will follow | Used to avoid ever committing to a number |
This table is judgement drawn from how building contracts are structured, not a published dataset. It is here to be argued with.
Source verification, this site · 30 July 2026
Why renovation is different
A new build has no history. Your house has a hundred years of it.
The reason this decision matters more on a renovation than on a new build is structural, not cultural. A new house is built in one sequence on a clear site: the unknowns are weather, ground conditions and supply. An alteration has to meet an existing building that was constructed to a different standard, has been modified by people who left no drawings, and may have been quietly wet for twenty years.
That is why the weathertightness split matters so much here. When New Zealand’s failures were costed, the estimated failure rate for monolithic and stucco cladding was 95% against 2% for weatherboard. If your house is in the first group, a fixed price given without invasive moisture investigation is not a fixed price — it is a number waiting to be revised.
It is also why "no consent needed" is rarely the good news it sounds like. Work that avoids a consent is not necessarily work that avoids surprises. Where the consent line actually falls.
BRANZ Study Report SR142, House Condition Survey 2005 · 2005
Questions people actually ask
Which is cheaper, fixed price or charge-up?
Neither, reliably. A fixed price includes a premium for carrying risk you would otherwise carry yourself; charge-up removes that premium and hands you the risk. On a well-defined job in a sound building, fixed price usually costs a little more and is worth it. On an unopened older house, a fixed price either carries a large allowance or will be renegotiated by variation — which is charge-up with extra paperwork.
What makes a variation legitimate?
Something genuinely outside the agreed scope, priced and agreed before it is done. Rotten framing found when a wall opens is legitimate. Work that was always necessary but was left out of the quote to win it is not. The defence against both is a written scope and a written variation process.
Do I need a written contract?
For residential building work at or above the Building Act threshold, a written contract is required and the builder must give you prescribed disclosure information before it is signed. Below the threshold it is still the single cheapest piece of protection available. Ask which basis the price is on — fixed, charge-up, or fixed with a schedule of allowances — and get it in the contract.
Next
Where to take this
Comparing three quotes
Six questions that force three quotes onto the same scope, plus a labour model.
The real sequence
Where a renovation programme actually loses weeks, and which stages you can protect.
What it costs
What Auckland consent declared values support, and what they do not.
Send a brief
The job first, your phone number last. One conversation.