Precast Concrete: Why Erection & Cranage Is Priced Separately From Supply

Precast concrete elements — panels, columns, beams, or plank — are cast off-site at a controlled facility and delivered ready to install, which is exactly what makes them fast to erect but also what splits their cost into two genuinely separate line items: the supply cost of the piece itself, and the erection cost to lift and set it in place.

Supply Cost: A Fixed Per-Piece Number

Once a precast piece's design is finalized, its supply cost is close to fixed — it's manufactured to spec regardless of which specific project it ends up on, priced per piece or per cubic meter depending on the element type. This is the number that scales predictably with quantity: twice as many identical panels costs close to twice as much to supply.

Erection Cost: A Function of Site Conditions, Not Piece Count Alone

Erection and cranage cost depends on factors that have nothing to do with the piece's own manufacturing cost: crane capacity needed for the heaviest piece on site, site access and crane positioning, mobilization and demobilization of the rig itself, and the sequencing of the erection schedule. A project with difficult site access can have erection costs that dwarf the supply cost of the pieces being lifted, even though the pieces themselves are unremarkable.

What to Check on a Precast Estimate

Confirm crane capacity against the heaviest single piece, not the average — a schedule with one unusually heavy element can force a larger, more expensive crane for the entire job. And confirm mobilization is priced once per crane visit, not accidentally duplicated across every precast line item on the BOQ.

Worked Example: Fifty Identical Panels

Fifty identical precast wall panels, once the design is finalized, have a supply cost that scales almost linearly with quantity — panel 50 costs roughly the same to manufacture as panel 1. Erection cost doesn't follow that same pattern: crane mobilization and demobilization is typically a single lot-sum cost regardless of whether the crane is lifting 10 panels or 50, and the crane capacity required is set by the single heaviest panel on the project, not the average panel weight. A project with 49 lightweight panels and one unusually heavy one still needs a crane rated for that one heavy piece — the other 49 panels don't reduce that requirement at all.

Common Mistakes

The most common estimating mistake is folding erection and cranage into a per-piece rate as if it scaled the same way supply cost does — it doesn't, and a per-piece erection rate built from an average tends to badly misprice both very small and very large precast packages. A small package still absorbs a full crane mobilization cost spread across few pieces, driving the effective per-piece erection cost up; a large package with one unusually heavy element forces a larger, more expensive crane class for the entire job, not just for that one piece. The second common mistake is duplicating mobilization cost across multiple precast line items on the same BOQ, when in practice one crane visit typically covers the entire precast erection scope in a single mobilization — that cost should appear once, not once per element type.

Quick Reference

Supply cost scales with piece count. Erection cost scales with crane requirements — set by the heaviest single piece and the site access conditions, not the average piece weight. Keep the two as genuinely separate line items rather than blending them into one per-piece rate, especially on packages with a wide weight range across pieces.