Ten centimetres too high

An annex to an existing building: a plant room for an air handling unit. Timber post structure, mono-pitch roof. The foundation was set at a height nobody verified against the building's target height. Once the walls were up it turned out the annex roof would land above the roof of the main building — and then you cannot run the fall and the flashing correctly at the junction. The fix: drop the ceiling by ten centimetres. The unit takes up about half the room. The installer set it to the drawing. On that basis the roof was closed and a penetration was cut for the ducts running outside. A week later the services designer arrives, measures, and repositions the unit — with the roof ten centimetres lower there is no longer the required clearance above the unit to run the ducts. Once moved, the penetration has to be elsewhere: right next to the one already cut.

• Dropping the ceiling — rework on a finished structure, not at the planning stage • Double installation of the unit — two crew mobilisations instead of one • A second roof penetration — a new opening beside the existing one • Sealing the first penetration — the priciest item, invisible today in any breakdown: a patched roof penetration is a permanent weak point in the waterproofing, a defect that surfaces years later • Spare parts from the manufacturer, with a lead time nobody planned for • Slippage for the crews next in line The amount above is the rework labour alone — no parts, no second crew mobilisation, and none of the cost of the sealed penetration. A dimensional error at the start does not stay at the start. It propagates up the structure and changes owner along the way. One crew set the foundation, a second dropped the ceiling, a third closed the roof, a fourth installed the unit, a fifth ordered the correction. Each did their own work correctly against what they found. That is why the cost can be pinned on no one — it dissolves into overheads, because no single person did anything wrong. What was done wrong was one flow of information that nobody owns.