Prefab Spools Spend Money Three Months Before Install
The shop cuts duct and welds spools in month three for work that installs in month six. If that cost sits in overhead, every job reads rich and the shop reads like dead weight.
Trades without a shop have one simple rule: cost happens on site, on the day the work happens. Mechanical builds a serious chunk of the job indoors, weeks ahead of installation, so unless a shop rate carries that cost onto the job, WIP is measuring installed percent against a cost base with the prefab missing. The more you prefab, which is the whole point of running a shop, the further off the numbers get.
The size of it
Gross margin on every prefab heavy job reads 8 to 12 points high until the job closes and the real number hits all at once, usually in the month you were planning to take a distribution.
The coil line and the pipe fab bay spend real money in month three on duct sections and welded spools that go in the building in month six. That's labor, metal, and machine burden gone before the material ever ships to site. When shop labor and shop burden get booked to an overhead department, the job's cost to date is understated and the WIP schedule shows overbilling that doesn't exist. The shop itself then reads like a fixed cost nobody can defend at year end. Both readings are wrong at the same time, which is why the numbers never quite explain the bank balance.
Three moves, in order
Step 02: Equipment cost basis
A true internal rate per machine covering ownership, maintenance, fuel, and transport, charged to the projects that used it.
What else costs mechanical contractors money
The same mechanism in other trades
What mechanical owners ask
Should fab shop labor go to job cost or overhead?
The shop cuts duct and welds spools in month three for work that installs in month six. If that cost sits in overhead, every job reads rich and the shop reads like dead weight.
What does it cost?
Gross margin on every prefab heavy job reads 8 to 12 points high until the job closes and the real number hits all at once, usually in the month you were planning to take a distribution.
What do I do first?
Build a shop rate: shop labor plus burden plus machine and facility cost, divided by budgeted shop hours. Recalculate it quarterly, not once.
What are mechanical contractors supposed to be making?
Mechanical runs 25% gross margin, 16% overhead and 9% net profit before taxes at $1M–$5M. The all-trade average is 7%, so this trade sits 2 points above it. The CFOS target is 11%.
Which part of the system fixes it?
The step is number 02, equipment cost basis. A true internal rate per machine covering ownership, maintenance, fuel, and transport, charged to the projects that used it. It comes from chapter 2 of CONTROL: The Construction Financial Operating System.
Josh Luebker ran commercial construction projects before he ran the numbers behind them, on data centres, military bases, hospitals, and high-rises. He wrote CONTROL: The Construction Financial Operating System, which is an eight-step framework for commercial subcontractors, and it publishes on October 1, 2026. He is a master electrician who moved into the office and kept the field vocabulary.
Sulphur Prairie Operations LLC maintains the benchmark reference behind these figures. Every edition is reconciled against the newest CFMA survey release before it publishes here. Where a figure changes between editions, the older edition keeps its year in the title so a citation to it stays correct.