The short version
- Waste is not one number. It ranges from about 2% on cut-to-length steel to 20% or more on patterned tile and small-diameter fittings.
- Two different things get called waste: material lost in the cut, and material bought in a fixed purchase unit you cannot use in full.
- Geometry drives it more than workmanship. A cut-up plan with many small rooms wastes sheet goods no matter who hangs them.
- Show the factor in its own column. Buried in a rate it cannot be argued with, checked, or reused on the next job.
Two different things wearing the same label
Before the numbers are useful you have to separate them. Cutting waste is material that leaves the job as offcut: the end of a stud, the strip off a plasterboard sheet, the length of pipe past the last fitting. Purchase waste is material you buy but never use, because it only comes in a fixed unit. A tin of adhesive covering 40 square metres on a 45 square metre floor is 35 square metres of purchase waste, and no amount of care on site recovers it.
They behave differently. Cutting waste scales with the quantity, so a percentage works. Purchase waste is a step function, so a percentage understates it badly on small jobs and overstates it on large ones. On anything under roughly 200 square metres of a finish we round to whole purchase units instead of applying a factor, and we say so in the assumptions.
The table
| Material | Typical | Range | What pushes it to the top of the range |
|---|---|---|---|
| Ready-mix concrete, slabs | 4% | 3% to 7% | Sub-base over-dig, pump losses, part loads on small pours |
| Ready-mix concrete, footings | 7% | 5% to 12% | Unformed trench fill in soft or running ground |
| Reinforcement bar | 5% | 3% to 10% | Short bar schedules, heavy lapping, no bending schedule issued |
| Mesh reinforcement | 12% | 10% to 15% | Laps counted at 200mm or more against an irregular slab edge |
| Structural steel, cut to length | 2% | 1% to 4% | Non-standard sections mill-ordered rather than taken from stock |
| Timber studs and joists | 8% | 5% to 12% | Non-modular ceiling heights, many short walls |
| Sheathing and plywood | 10% | 7% to 15% | Cut-up roof planes, dormers, curved or raked walls |
| Plasterboard and drywall | 10% | 8% to 18% | Small rooms, many openings, high ceilings needing part sheets |
| Insulation, batt | 6% | 5% to 10% | Irregular joist centres, service voids, friction fit trimming |
| Insulation, rigid board | 8% | 6% to 14% | Detailed reveals and cutting in around penetrations |
| Brick and block | 5% | 3% to 8% | Feature bonds, tight cuts at reveals, cut face brick specials |
| Mortar | 15% | 10% to 25% | Site-mixed in small batches, spillage on scaffold |
| Floor tile, straight lay | 8% | 5% to 12% | Rooms not squared to the tile module |
| Floor tile, diagonal or patterned | 15% | 12% to 25% | Herringbone, large-format tile, out-of-square walls |
| Sheet vinyl and carpet | 12% | 8% to 20% | Roll width against room width, pile direction fixed |
| Roof tile and slate | 7% | 5% to 12% | Hips, valleys, and a low pitch needing wider laps |
| Single-ply membrane | 10% | 8% to 15% | Many upstands and penetrations against a small roof area |
| Paint | 5% | 0% to 10% | Tin sizes against a small area, plus a colour with poor coverage |
| Conduit and small-bore pipe | 10% | 8% to 20% | Congested ceiling voids, many short drops and offsets |
| Cable and wire | 8% | 5% to 15% | No containment route drawn, so runs are estimated generously |
| Ductwork, rectangular | 6% | 4% to 10% | Bespoke fabrication with high offcut on transitions |
Geometry beats workmanship, almost every time
The instinct is to raise the waste factor when a subcontractor has been careless. In practice the drawing tells you more than the crew does. Take plasterboard. On an open-plan office floor with 3 metre ceilings, a good hanger will land near 6%. Give the same crew a hotel floor of identical bedrooms at 2.4 metres with a bathroom pod in each, and 15% is honest work. Nothing about the labour changed. The number of cuts per square metre did.
That is why we take a wall count and an opening count off the plan rather than reaching for a default. If a floor has more than about one internal corner per 8 square metres, the sheet goods factor goes up and we note the reason on the line.
Where the ranges came from
These are our working figures, taken from closed-out jobs where we could compare the estimated quantity against what was actually delivered to site. They are not published standards and we would not defend them as such. Published tables exist and they are a reasonable cross-check, but they describe an average project, and there is no such thing as an average project when you are pricing one.
If your own delivery records disagree with a figure here, your records win. That is the whole point of keeping the factor in its own column. It is a number you can tune, on your jobs, in your region, with your suppliers.
How to present it
- Give waste its own column, next to the measured quantity, never folded into the rate.
- Show the resulting order quantity separately, so purchasing works from a figure they can see.
- Write the reason on any line above the typical figure. "18% board, 42 internal corners" survives a review meeting. "18%" does not.
- Round to purchase units on anything sold in tins, rolls, pallets or bundles, and say so.
- Keep the factors in one place rather than typing them into each job, so a lesson learned on one project reaches the next one.
Every workbook we issue is built this way, with quantity, waste and the resulting order quantity on separate columns. It is a small formatting decision that decides whether the number can still be argued with a year later.
Written by the estimating team at QuantX Estimation. Since 2016 we have measured and priced construction work for contractors in the United States and United Kingdom, at a fixed fee agreed before we start.
