Articles · 2026-09-07 · 4 min read
Twenty-five millimetres of slab, priced
Six rationalisations of ordinary elements, priced at published Q1 2025 rates for London and New York, with the arithmetic shown.
Twenty-five millimetres off a flat slab does not sound like money. Across eight floors of 1,000 m² it is 200 m³ of concrete, which at London supply rates for 30 MPa concrete (£175/m³, Q1 2025) is about £35,000, and at New York installed rates ($1,046/m³ placed in slab) about $210,000 (Turner and Townsend, Global Construction Market Intelligence 2025).
The examples page walks six such changes: a slab, a basement retaining wall, a run of columns, a set of floor beams, pad footings and the lightest-section exercise on a steel frame. Each states the assumed building, the concrete and steel saved, and the money at both rate brackets.
Three habits that keep the numbers honest
- Quote the rate by name and date. Material supply and installed composite rates differ by a factor of three or more between cities.
- Do not sum examples from different buildings. Each is its own arithmetic.
- On steel, price the frame, not the tonnes. Material is 30 to 40% of frame cost; fabrication and erection do not fall in step with mass.
What is not counted
Formwork, cranage and programme are left out, and so is the knock-on: a lighter floor means lighter columns and smaller footings, which is usually where the second half of the saving lives. The figures are estimates for the engineer of record to confirm, and a good place to start the value-engineering conversation.