The theory of lean construction is that projects are temporary production systems linked to multiple, enduring production systems, from which the project is supplied materials, information, and resources. Every production system integrates designing and making a product. Project management is understood in terms of design, operating, and improving production systems.

The current forms of project delivery in construction aim to optimize the project activity by activity and assumes that customer value has been identified in design. Each activity is broken down and either contracted out or assigned to a task leader. If activities or sequences of activities in the critical path fall behind, efforts are made to reduce the cost and duration of the activity or sequence. It is often necessary to adjust the work sequence, trading cost for time and in some instances sacrificing quality.

In lean construction, the reliable release of work between specialists in design, supply, and assembly (execution) assure that value is delivered to the customer and waste is reduced. Lean construction challenges the belief that there always must be a trade off between time, cost, and quality.

Project activities are interdependent. They share resources and the sequence and timing of tasks within one activity constrain downstream activities. Current project management practice cannot provide for this interdependence. As a consequence, waste abounds and value is lost under pressure to optimize cost and meet schedule deadlines.

In lean construction, the facility and its delivery process are designed together to better support the customer’s requirements. Work is structured throughout the process to maximize value and reduce waste at the project delivery level. Efforts to manage and improve performance are aimed at improving total project performance rather than just at reducing cost or increasing the speed of any activity. Control is redefined from “monitoring results” to “making things happen.” The performance of planning and control systems are measured and improved.

From: “Microelectronics: Lean Project Delivery For Cleanrooms and Contamination Controlled Facilities”