Formwork Contact Area Takeoff for Slabs, Beams, and Columns
Formwork is priced by the square metre of contact surface. Each structural element has its own counting convention — get those and the takeoff is quick.
Contact area rules by element
| Element | Formwork area |
|---|---|
| Suspended slab | soffit area (L × W); add edge form = perimeter × thickness |
| Beam | 2 × side depth + bottom width, × length (3 faces; deduct slab thickness from sides) |
| Column | perimeter × height |
| Wall | 2 × face area (both sides) |
| Footing (in open cut) | perimeter × depth; nil if cast against earth |
From area to materials
- Plywood / phenolic board: contact area / sheet area, ± a reuse factor. Phenolic board reused 3–5 times; divide total area by the reuse count for the order quantity.
- Joists and bearers: timber (50 × 100 mm) at ~0.6 m spacing for joists, ~1.0 m for bearers — length ≈ area / spacing.
- Props / shoring: one adjustable prop per ~1.0–1.5 m² of slab soffit, adjusted for slab thickness and prop capacity.
- Form ties and clamps: for walls and deep beams, per manufacturer spacing (typ. 400–600 mm grid).
Reuse and wastage
State the assumed number of uses in the BOQ — it changes the plywood quantity by 3–5×. Add 10% wastage for cutting around penetrations and damaged panels.
Stripping time affects the estimate
Sides can strip in 1–2 days; slab soffits and beam bottoms need 7–14 days (or reshoring). Longer stripping times mean more sets of formwork on site at once — a hire-cost and quantity driver.
EngEst Pro computes formwork contact area per element as you enter slab, beam, and column dimensions, applies your reuse factor, and lists phenolic board, coco lumber, and props in the structural BOM.
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