Lean construction is a way of organising building work so that as little waste as possible is built into the process and the work runs without interruption. The focus is not on keeping every gang fully occupied, but on the flow of the work itself: each following trade should find its work area clean, complete and available on time.
The approach comes from the motor industry — the Toyota production system — and was translated to construction from the 1990s onwards. Translation was necessary because a building site is not an assembly line: the product stands still and the gangs move around it.
The seven classic wastes
On site they are immediately recognisable:
- Waiting — for the preceding trade, for materials, for a decision or for an inspection.
- Transport — material moved three times across the site before it ends up in place.
- Inventory — pallets standing in the way for weeks, getting damaged and obstructing the work.
- Motion — walking to the skip, to the tools, to the drawing.
- Overproduction — doing work too early, so it gets damaged or has to be opened up again.
- Over-processing — building it neater or heavier than was asked for.
- Defects and rework — by far the most expensive item.
How it works in practice
- Last Planner System. The gangs who actually do the work draw up the short-term programme together, instead of receiving it. Site manager, carpenter, service engineer and plasterer sit at the same table.
- Pull planning. You start from the handover date and work backwards: what has to be finished before I can start? Dependencies surface that stay invisible in a bar chart.
- Weekly planning with commitments. Everyone commits to what they will finish that week. Whatever does not get finished is not glossed over but discussed: what caused it?
- Takt planning. The building is divided into equally sized work zones (takts) through which the trades move at a fixed rhythm — one apartment further each week, for instance. Calm and predictability produce more speed than working flat out.
- Daily huddle. A short stand-up meeting on the spot about the day’s work and where the bottlenecks are.
What it delivers, and where it goes wrong
The biggest effect is not in working faster but in less standing idle and fewer defect costs. Every part of that you remove is money straight back.
Pitfalls:
- Lean as a picture on the wall. Sticking up yellow notes without changing how decisions get made achieves nothing.
- Only the main contractor takes part. Without the subcontractors and services trades at the table, the programme is one-way traffic again.
- Planning too finely. A programme worked out to the quarter hour survives on no site.
- Penalising missed commitments. As soon as it becomes unsafe to say something will not work, the very information the method depends on disappears.
- No buffer. Lean does not mean squeezing all slack out of the programme; it means putting the slack deliberately where it belongs.
Related terms
- Construction process
- BIM
- Site set-up
- Tendering
- Defect costs
- Sustainable building
- Circular economy
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