Accounting for Material Waste and Shrinkage on Jobs

The Factor Everyone Uses and Nobody Checks

Estimates carry waste allowances: 5% on drywall, 10% on trim, 3% on structural steel, whatever your estimating software defaults to. The numbers came from somewhere, usually a previous employer or a textbook, and they are rarely revisited.

Meanwhile the actual waste on your jobs is knowable, and comparing the two is one of the faster ways to find money.

Waste and Shrinkage Are Different Problems

Waste is material consumed but not installed — offcuts, breakage, mixing losses, over-ordering. It is a production issue and it is partly unavoidable.

Shrinkage is material that left without being used. Theft, mis-delivery, material moved to another job and never recorded.

They show up identically in the accounts — material cost exceeds installed quantity times unit price — but they call for completely different responses. Waste is addressed by planning and cutting practice. Shrinkage is addressed by control.

Measuring Actual Waste

You need two numbers per material code: quantity purchased and quantity installed. Purchased comes from invoices. Installed comes from the same quantity capture that drives productivity tracking — which is why the two initiatives belong together.

Actual waste is purchased minus installed, over installed. Compare it to the estimate:

• Estimated 8% waste on drywall, actual 7% — the factor is right, no action.
• Estimated 8%, actual 19% — either the crews are cutting badly, the material is arriving damaged, or sheets are leaving site.
• Estimated 8%, actual 2% — your estimate is padded, and you are bidding higher than you need to.

That last case is worth as much as the others. Padded waste factors lose bids you should have won.

The Shrinkage Signal

Waste tends to be consistent for a given material and crew. Shrinkage is lumpy — normal for months, then a spike.

Patterns worth noticing: waste elevated on one job and normal elsewhere with the same crew; high-value, easily resold materials — copper, fixtures, tools, appliances — showing consistently higher loss than bulk materials; and a spike following a delivery that nobody signed for.

None of these prove anything on their own. All of them justify asking.

Where It Sits in the Books

Waste within the estimated allowance is simply job cost. There is no separate entry to make, because the estimate already contemplated it.

Waste materially above the allowance is still job cost — it happened on that job — but it should be flagged in the variance review as a quantity variance rather than absorbed silently.

Material confirmed stolen is different. It is a loss, not a cost of building that job, and burying it in job cost distorts both that job's margin and your waste data for every future estimate. Write it off separately and keep the job cost honest.

A Practical Starting Point

Pick your three highest-value material codes. Track purchased against installed for one quarter. Compare to your estimating allowances and adjust them.

Most contractors who do this find at least one factor materially wrong in each direction — one that is costing them money on site, and one that is costing them bids.