Most of your cost is measured by someone who wants your money.

The superstructure reinforcement — 107 tonnes, from Week 4 — has been let to a specialist subcontractor at $1,285 a tonne. That is more than your own direct cost of $1,123.40, because his price includes his profit and his risk. You paid $17,291 for the privilege of it being his problem instead of yours.

It is month nine. His fourth valuation lands on your desk.

The claim and the measure

He says he has fixed seventy-eight tonnes. At $1,285, that is $100,230, and he would like it certified.

You walk the deck with the same tonnage sheet you have used all track. Sixty-three tonnes are tied into the wall and inspected. Fifteen tonnes are cut, bent, stacked on the deck, leaning against the formwork — handled, but not built.

He is not lying. He genuinely has touched seventy-eight tonnes of steel — he has paid men to cut and bend it, and from where he stands that is progress. But “handled” is not what the contract pays for. The contract pays for reinforcement fixed in place, and that is sixty-three tonnes.

The nineteen thousand dollars between his claim and your measure is not fraud. It is the structural fact of subcontracting: his valuation is an opening position, not a statement of fact. And it arrives every month, and every month you have to knock it back to what you can measure, and every month he tries again.

This is the whole job. Last week's six methods were a private discipline. Here they are a negotiation, and the tape measure is your only weapon.

From a claim to a cheque

A subcontract certificate is not one number. It is a build-up, and every line in it is a control you either use or surrender.

Start with his application: $120,910 — the seventy-eight tonnes plus twenty-two tonnes of steel sitting on site.

Strip the overclaim. Fifteen tonnes are not in the wall. Minus $19,275. You are now valuing sixty-three tonnes, because sixty-three tonnes is what exists.

Hold the materials on site. He wants $20,680 for the twenty-two tonnes under the tarpaulin, and this is the trap that has sunk more main contractors than bad rates ever have. Pay a subcontractor for materials on site, he goes into administration next week, and the liquidator owns that steel — you paid for it and you have nothing. The only protection is a vesting certificate: legal title passes to you before you release a penny. No vesting certificate, no payment. It is not unkind. It is the difference between owning the steel and owning a receipt.

Take the retention. Five percent, held back on every certificate, released half at practical completion and half at the end of the defects period. It is your insurance against him walking away with snags unfixed. On this certificate that is $4,048.

Subtract what he has already had. He has been paid $54,934 on previous certificates. Interim valuations are cumulative — you value the whole job to date and subtract everything certified before, so an error in an early month corrects itself in the next.

He applied for $120,910. He is entitled to $21,974. Certify the application instead of the work and you have handed a subcontractor $37,957 of your project in a single month, and you will spend the rest of the job trying to claw it back from a man who has already spent it.

Three ways the package turns on you

Over-valuation is only the first of three, and it is the mildest.

The second is the materials trap you just closed. The third is the one that keeps main contractors awake: insolvency. That subcontractor is holding 107 tonnes of reinforcement that sits directly on your critical path. If he folds — and specialist subcontractors fold all the time, often because a main contractor over-certified them into a false sense of health and then stopped paying — his scope stops overnight. You cannot pour the frame without rebar. Your programme dies with his company.

So the number you watch is not his progress. It is his cash. A subcontractor who is being paid roughly what he is spending is stable. One you have front-loaded is a company with your money and no incentive, and one you have starved is a company about to collapse on your critical path. Both are your problem, and neither shows up in a progress report.

Notice the symmetry with Week 9. Front-loading was you doing this to the client — taking money early against the easy work. Now you are the client, and a man whose interests run exactly opposite to yours is doing it to you, every month, with a straight face. Everything you learned to do to them, you must now learn to see coming.

The unpriced change

One more, because it is where the arguments live. Halfway down his valuation is a line you did not expect: eight tonnes of extra reinforcement in the column heads, which the engineer added by a drawing revision, and which he has priced as dayworks at $1,450 a tonne rather than his subcontract rate of $1,285.

He is trying to convert a change into new work at a premium rate. Sometimes that is legitimate — genuine additional scope, genuinely disruptive. Often it is a rate grab. Whether that eight tonnes is worth $10,280 at his agreed rate or $11,600 as dayworks is a real question with real money in it, and it is the entire subject of next week.

For now, one rule: a change is not certified in an interim valuation. It goes through a separate process, with its own record, or your monthly certificate becomes the place where scope quietly grows and nobody ever agreed to it.

Practical insight

Take your largest subcontract and pull the last valuation certificate. Find two numbers: what he applied for, and what you certified.

If they are the same number, month after month, you are not certifying — you are rubber-stamping, and somewhere in that package is a gap between what you have paid for and what is actually built.

Then find the materials-on-site line and ask one question: is there a vesting certificate? If money has gone out against materials with no vesting, you have an unsecured loan to a subcontractor, and you did not decide to make it.

Then ask the hardest one: if this subcontractor went under on Friday, what would it do to my programme? If the answer frightens you, his cash position is now the most important number on your project, and you should already know it.

Key takeaways

✔ On a main contractor's job most cost, and most measurement, belongs to subcontractors whose interests oppose yours.
✔ A subcontractor's valuation is an opening position. He claimed 78 t; you measured 63; the $19,275 gap arrives every month.
✔ A certificate is a build-up: application − overclaim − unvested materials − retention − previous payments. He applied for $120,910; he is due $21,974.
✔ Never pay for materials on site without a vesting certificate — or the liquidator owns the steel you paid for.
✔ Retention (5%, half at practical completion, half after defects) is your leverage. Interim valuations are cumulative, so early errors self-correct.
✔ Three risks: over-valuation, unsecured materials, and insolvency — and his whole scope is on your critical path.
✔ Watch his cash, not just his progress. Front-loaded or starved, a subcontractor is a threat either way.
✔ A change never gets certified inside an interim valuation. It goes through its own process — which is next week.

What is coming next

That extra eight tonnes in the column heads is the loose thread, and pulling it unravels the most argued-over money in construction.

When the drawing changes, what is the work worth? The rate in the bill? A new rate you negotiate? The cost of the men and plant, measured by the hour, whether they were efficient or not? And what about the work that was not changed but got slower because of the change — who pays for that?

Next week: pricing a change — bill rates, star rates, dayworks, and the quiet killer that is disruption.