Subcontract Scope Gap & Back-Charges: An NZ Subbie's Guide

Steve Parker
Jul 23
9 min read

Getting back-charged for work you never priced? Here is how the subcontract scope gap in NZ creates back-charges, and the pre-tender checks that stop it.

By Steve Parker · Trueworks · NZ construction estimation · 8 min

Most back-charges are not born on site — they are written into the subcontract weeks earlier, in the grey zone between what the head contract requires and what your subcontract actually says.

What you'll learn

Where scope gaps hide in an NZ subcontract before you ever lift a tool
The four structural traps that turn a grey zone into a back-charge
The pre-tender clause check that closes the gap, and how to test a disputed back-charge

Quick answer: A subcontract scope gap is the space between what the head contract obliges the main contractor to deliver and what your subcontract actually describes you as pricing. Back-charges are born in that gap: the head contractor docks your account for work that fell in the grey zone, arguing it was "flowed down" to you. The fix is at tender, not on site — confirm which head-contract documents are actually attached, line your inclusions and exclusions up against the head scope, get a defined completion obligation, and pin down who supplies the grey-zone items. If a back-charge is disputed, it can be tested through the payment claim and schedule regime and, if needed, Construction Contracts Act 2002 adjudication, and genuine extra work should be valued as an NZS 3910 §14 variation rather than quietly absorbed.

Where the scope gap actually lives

A subcontract scope gap is not a vague feeling that you have been hard done by. It is a specific, locatable space: the difference between the obligations the head contractor owes the principal under the head contract, and the obligations you signed up to under your subcontract. When those two documents do not describe the same scope, somebody has to absorb the difference. On most Auckland jobs, the subcontractor is the one holding the parcel when the music stops.

The trouble is that you rarely see the head contract. You price off a subcontract, a set of drawings, and maybe a specification — and you assume the subcontract describes your slice cleanly. It often does not. A "flow-down" clause says you take on the head-contract obligations "as if you were the contractor", but the actual head-contract schedules, programmes, and scope matrices that define those obligations are not attached. You have agreed to obligations you have never read. That is the gap, and the back-charge is what fills it.

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The four structural traps

Four recurring features turn a grey zone into a deduction off your account. Each is fixable before you sign.

1. Flow-down with nothing attached. A flow-down clause binds you to the head-contract terms, but the operative documents — the principal's scope, the schedule of quantities, the head-contract programme — are referenced, not attached. You inherit duties whose detail you cannot see. When a dispute lands, the main contractor reads the head scope to your detriment and points at the clause.

2. No defined completion date. If your subcontract has no clear completion obligation — just "in accordance with the main contractor's programme" — your time obligation floats. A back-charge for delay, or for "acceleration" the contractor says you caused, has nothing fixed to argue against. An undefined date is an open invoice waiting to be written.

3. Short look-aheads that hide programme risk. A rolling three-week look-ahead tells you the next 21 days and nothing about the structural sequencing risk further out. It feels like a programme; it is a fortnight of comfort over a year of exposure. When the build compresses and your window collapses, the cost of working out of sequence — or standing down crews — surfaces as a back-charge rather than an extension.

4. Inclusions and exclusions that do not line up with the head scope. This is the heart of it. Your subcontract lists what you include and exclude. The head contract describes a scope the main contractor must deliver. If your exclusions carve out items the head scope plainly requires — temporary works, set-out, making good, hoisting, protection of finished work — the main contractor still owes those to the principal. Guess who gets back-charged to plug it.

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How scope creep becomes a deduction off your account

Scope creep on a subcontract is rarely a single dramatic change. It is an accumulation of small "well, that's obviously part of your trade" assertions: you set out your own work, you protect it, you clean up, you hoist your own materials, you make good after others. Individually, each sounds reasonable. Together, they are an unpriced scope that grows after the price is fixed.

The deduction usually arrives one of two ways. Either the main contractor instructs someone else to do the grey-zone work and back-charges you the cost plus their margin, or they do it with their own labour and dock you. Because variations to a fixed scope attract no competitive tension once everyone is on site, the rate you get charged is almost always higher than what you would have priced it at yourself — commonly the base cost plus 10–15 percent overhead and margin, and sometimes a good deal more. The same dynamic that lets a main contractor add 20–30 percent on a stacked variation works in reverse when the charge is coming the other way.

This is also where the line between a legitimate back-charge and an opportunistic one gets blurred. A genuine back-charge recovers a real cost the contractor incurred because you failed to do something you were clearly obliged to do — defective work you would not return to fix, rubbish you left, damage you caused. A scope-gap back-charge recovers the cost of work that was never clearly yours in the first place. The contract documents decide which is which, and that is why the documents have to be right before you sign, not after.

Scope-gap zones, the back-charge they produce, and the check that prevents it

| Scope-gap zone | Typical back-charge | Pre-tender check that prevents it | |---|---|---| | Flow-down clause with no head-contract schedules attached | Charged for an obligation buried in head scope you never saw | Ask in writing which head-contract documents are incorporated, and get the relevant scope, schedule and programme actually attached | | Temporary works, set-out, protection, hoisting | Main contractor does it and docks you "because it's your trade" | List these explicitly as included or excluded, and confirm against what the head scope assigns | | No defined completion date | Delay or acceleration charge with no fixed date to argue against | Negotiate a defined completion obligation, or sectional dates, written into the subcontract | | Short rolling look-ahead hiding sequencing risk | Out-of-sequence or stand-down cost passed to you | Ask for the full head-contract programme and the milestone dates that bind your window | | Making good and clean-up after other trades | Cleaning or remedial bill for work others damaged | Limit your make-good and clean-up to your own work, in writing | | Provisional or grey-zone supply (who supplies what) | Charged for materials each party assumed the other was supplying | Resolve every supply boundary item-by-item before pricing |

The pre-tender clause check

Closing the gap costs nothing at tender and a great deal afterwards. Before you submit a price, work through this.

Read the flow-down clause and demand the documents. If the subcontract incorporates the head contract "as if", ask in writing exactly which head-contract documents are incorporated and get them attached. A reference you cannot read is an obligation you cannot price.
Map your inclusions and exclusions against the head scope. Take your scope list and the head scope side by side. Any item the head scope requires that your exclusions push away is a gap the main contractor will close at your expense. Either price it or get it formally assigned elsewhere.
Pin down a completion obligation. Get a defined date, or sectional completion dates, into the subcontract. "Per the main contractor's programme" is not a date — it is a moving target you cannot defend a delay back-charge against.
Get the real programme, not a three-week window. Ask for the head-contract programme and the milestones that govern your access and your finish. Understand the sequencing risk before you commit, not after the build compresses.
Resolve every grey-zone supply boundary. Temporary works, set-out, hoisting, protection, making good, clean-up, consumables — for each, write down who supplies and who does it. Ambiguity here is the single richest source of back-charges.
Tie genuine extras to a variation, not absorption. Where the contractor instructs work beyond your defined scope, treat it as a variation and value it accordingly. On NZS 3910 contracts the §14 valuation hierarchy runs agreed price, then contract rates, then reasonable rates, then daywork — use it rather than swallowing the cost to keep the peace.

The same discipline you would apply to head-contract risk applies here. Running a pre-tender risk register over a subcontract surfaces these gaps in an afternoon, and the logic of catching scope gaps on multi-dwelling work carries straight across to a repetitive subcontract package where one missed exclusion multiplies across every unit.

How to test a disputed back-charge

A back-charge is not a deduction you have to accept on sight. If the contractor reduces your payment, the Construction Contracts Act 2002 still governs payment. A deduction should appear as a reason in a payment schedule responding to your payment claim, with the amount and the reason stated. If you serve a valid payment claim and the contractor fails to issue a compliant payment schedule in time, the contractor can become liable for the full claimed amount — so keep claiming properly and on time, and read every schedule line by line.

Where you genuinely disagree, the CCA gives you a fast statutory route: adjudication. It is built to resolve exactly this kind of contractual dispute quickly, and it puts the question — was this back-charge owed, and under what part of the contract — to an independent adjudicator rather than leaving it to whoever holds the cheque book. Note too that pay-when-paid clauses are void, so a contractor cannot defend a withheld payment by saying the principal has not paid them.

This is general information, not legal advice — get advice on your specific contract.

FAQ — subcontract scope gaps and back-charges in NZ

Q1: What is a subcontract scope gap? It is the space between what the head contract obliges the main contractor to deliver and what your subcontract actually describes you as pricing. When the two documents do not match, the difference has to be absorbed by someone, and back-charges are how it usually lands on the subcontractor.

Q2: Can a head contractor back-charge me for work I never priced? Only if the contract documents put that work in your scope. A legitimate back-charge recovers a real cost from something you were clearly obliged to do and did not. If the work fell in a grey zone your subcontract never assigned to you, the back-charge is contestable — which is exactly why your inclusions, exclusions and the attached head-contract documents matter so much.

Q3: What are flow-down clauses in a subcontract? A flow-down clause binds you to the head-contract terms as if you were the main contractor. The risk is that the operative head-contract schedules and scope are often referenced but not attached, so you inherit obligations you have never seen. Always ask in writing which documents are incorporated and get the relevant ones attached before you price.

Q4: How do I stop scope creep on a subcontract? Resolve the grey-zone items before you tender. Map your inclusions and exclusions against the head scope, name who supplies and does each ambiguous item — set-out, temporary works, hoisting, protection, making good, clean-up — and get a defined completion date. Most scope creep is just ambiguity that nobody nailed down at tender.

Q5: What can I do if I disagree with a back-charge in NZ? Make sure the deduction is documented in a payment schedule responding to your payment claim under the Construction Contracts Act 2002, and challenge it line by line. If you still disagree, you can take the dispute to statutory adjudication, which is designed to resolve contractual payment disputes quickly and independently. Genuine extra work should be valued as a variation under NZS 3910 §14, not absorbed.

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About Trueworks

Trueworks is built by Steve Parker — 20 years on the analytical side of NZ construction. Variation reviews, contract advisory, programme review, and AI-augmented document workflows. Trueworks is the productisation of that practice for builders: same defensible analysis, at a price and pace a NZ builder can actually use.

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steve@trueworks.co.nz · trueworks.co.nz

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