📋 Estimating / BOQ · 6 min read
Wastage and Allowance Factors by Material
Wastage is real cost and it belongs in the estimate — as an explicit line, at a rate you can justify, not as a vague round-up.
Typical factors
| Material | Wastage / allowance |
|---|---|
| Ready-mix concrete | 3–5% (spillage, over-excavation, test cylinders) |
| Site-batched concrete | 5–8% |
| Reinforcing steel | 3–5% offcuts + laps counted separately |
| CHB / blockwork | 3–5% breakage |
| Ceramic / porcelain tile | 7–10% (10–15% for diagonal or small rooms) |
| Structural timber / formwork ply | 10% + reuse factor for ply |
| Paint | 5–10% brush/roller, 15–40% spray |
| Electrical cable | 10–15% (terminations, slack, offcuts) |
| Pipe (supply/drainage) | 5–10% |
| Aggregate / fill | bulking + 5–10% spreading loss |
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Don’t double-count
- Laps (rebar, mesh, membrane) are an allowance, not waste — count them in the net quantity, then add a small waste percentage on top.
- Bulking (soil, aggregate) is a state conversion, not waste — apply it first, then add spreading loss.
- Cover / minimum order (paint tins, cable drums, tile boxes) rounds the final quantity up — apply after waste, not instead of it.
Adjust for the job
Small, cut-up areas waste more than large open ones. Difficult access, poor storage, and inexperienced crews push factors to the top of the range. Repetitive high-rise floors trend to the bottom. State your assumption so a reviewer can challenge it.
📋 Using EngEst Pro
EngEst Pro applies a material-specific wastage factor to every quantity and shows it as a separate allowance in the BOM — so you can see the net quantity, the waste, and the ordered quantity side by side.
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