Construction projects often suffer from inefficiency: workers standing idle, materials ready but no crew available, and vice versa. This stems from variation in production – inconsistent processes leading to unpredictable results. While inevitable, variation is a core problem in Lean Construction, and addressing it unlocks significant productivity gains.
Understanding Variation
Variation isn’t random chaos; it falls into two categories: common cause and special cause. Common cause variation arises from the inherent properties of a process – worker experience, motivation, or inconsistent procedures. Special cause variation stems from external factors: weather, equipment failure, material delays, or design errors. Both types disrupt workflow, causing trades to be either underutilized, overstretched, or constantly fluctuating between the two.
The Goal: Reliable Workflow
The aim isn’t simply to predict workflow (knowing what will happen) but to make it reliable – consistently stable over time. Reliable workflow means predictable starts and releases of work, allowing for efficient sequencing and resource allocation. The Last Planner® System was developed specifically to increase this reliability by focusing on commitment-based planning and constraint removal.
A Three-Step Strategy for Reducing Variation
Minimizing variation requires a deliberate approach. Here’s a three-step process:
1. Implement Buffers
Buffers absorb the impact of variation without eliminating the root causes. Three types exist:
- Size/Inventory Buffers: Excess materials on-site reduce supply chain disruptions.
- Capacity Buffers: Extra resources absorb demand spikes (less common in construction).
- Schedule Buffers (Workable Backlog): Work outside the critical path provides a backup plan for unforeseen delays. This is a standard practice in Lean projects.
While useful, buffers are temporary solutions. The goal is to reduce reliance on them over time.
2. Reduce and Remove Variation
Continuous improvement is key. Tap into the collective expertise of the workforce to identify better ways of working. Pull planning sessions with frontline workers are essential for developing realistic execution plans. Collaboration is the foundation of a stable process.
3. Lower the River
This refers to exposing hidden system problems by gradually reducing safety nets. For example, reducing on-site material stock reveals inefficiencies in procurement and logistics. This forces proactive problem-solving rather than masking issues with excess inventory.
The Payoff: Real Flow
Addressing variation isn’t just about avoiding waste; it unlocks flow. With predictable work releases and reliable sequencing, idle time decreases, and value creation accelerates. The result: less waiting, more doing, and a more efficient construction process.
Ultimately, focusing on variation reduction isn’t just good practice; it’s fundamental to achieving true Lean construction
