Lean principles in the construction industry

The construction sector is one of the main pillars of economic growth and country development for all nations across the globe, and a link in the chain of dependencies between all industries in terms of consuming inputs and providing products. Nonetheless, it is estimated that 50% or more of the required resources and effort as to deliver the built environment consists in waste, or non-added value effort. The same lack of effectiveness of the labor hour in the past 50 years has caused for the construction industry to fall behind in the terms of major advancements. Over time, the workforce landscape has also changed due to demographic and labor shifts, reducing the labor availability and consequently increasing the relative cost of a built environment.

Lean construction is a robust approach that attempts to reduce waste in the construction projects, enhance performance and cut down cost for the industry and the society on a larger scale. The concept first emerged in the 80's after gaining full acceptance in the West due to the major improvements displayed in the manufacturing operations and has its roots in Toyota's production management principles.

This article aims to answer the following research questions:

• How are the construction projects different from manufacturing operations?
• How can the Lean principles be tailored for this sector based on this analysis?
• What limitations need to be considered before seeking to include elements of this methodology in the planning phase?
• What are some recommended directions and tools that can be included?

Its structure will take the reader through a brief history of the concept by presenting the Toyota story, the takes from it and the key differences between manufacturing and construction projects, the five traditional core principles of the Lean management and the waste sources in the targeted projects, implementation directions and limitations.

Big idea

History

The concept of Lean stems from Toyota's Lean production, also known as Toyota Production System (TPS), which fundamentally applied precast construction principles to their manufacturing processes with the end goal of creating a leaner organization.

The core concepts of TPS and their intercorrelation can be visualized in a structured manner through the TPS house, consisting of two pillars supporting a roof and a foundation. A good understanding of this is essential for developing and improving a lean system which will subsequently aid the company in removing waste and non-value adding effort, resulting in increased efficiency and maintenance of superior value and quality.

-insert figure-

As it can be observed, the procedure puts much emphasizes on the supply chain's speed. The underlining trend is to shorten the lead time by reducing or completely eliminating waste at each step in the process to produce the best quality, at a low cost, delivered on-time, while also enhancing safety and morale, principles known as QCDSM.

Nonetheless, a successful implementation of TPS requires more than adopting and applying a set of tools, methods and techniques. It demands a pervasive and intensive cultural transformation at a company level and the development of a strong collaborative relationship with the suppliers, which will lead to quality materials being delivered consistently and productively.

Lean core concepts and principles

Toyota's methodology was subsequently disseminated and researched on by multiple authors, Womack and Jones proposing 5 core principles :

1. Value: defined through discussions with the ultimate customer. The complexity of identifying it increases in construction projects where there is not a single ultimate customer, but the construction client and multiple end customers alongside to be taken into consideration. Additionally, understanding the customer's needs implies both defining the end product or service and the preferred procedure for obtaining it.
2. Value stream: analyzes three types of actions - activities that generate value, non-value adding activities which remain unavoidable due to current technological and production constrains and non-value adding activities that can be avoided.
3. Flow: after reducing or completely eliminating waste, all the remaining steps of every process need to flow, so the product can be delivered from concept to client without delay or interruption. This involves eliminating batch and queue, and some recommended methods are restructuring the production, training the employees to be skilled in multiples areas and adaptive, delegating the workload to more than one asset.
4. Pull: close to TPS's original pull system, this principle aims to tailor the production to the customer's requirements in terms of quantity and delivery time and save inventory space and materials in the process.
5. Pursue perfection: through the application of the previous four principles in a continuous loop, the company can identify and reduce hidden waste, highlighting the need to adopt the Lean principles as an integrated part of the work environment.

The relation between these steps can be visualized in figure -insert figure-.

In essence, Lean production takes place at both a strategic and an operational level. Strategically, it equips the organization with a structured approach of defining the customer value and identifying the value stream and, at an operational level, it provides multiple tools and practices for eliminating waste and integrating permanent improvement.

From manufacturing operations to construction projects

Fundamentally, transferring these Lean principles from the manufacturing production to the construction industry has its limits since the two domains operate on different grounds. The manufacturing processes are performed in a factory-controlled environment in which the production line follows a clear flow with easy to identify steps and constraints, there is a mass-produced with little variation output and minor fine-tuning from one project to another.

Whereas the construction projects involve a much higher level of complexity as each one of them presents a unique frame of physical, social and environmental traits. Moreover, the planning phase takes into account a more dynamic context, as opposed to the previously described isolated system, with often concurrent activities that need to be scheduled accordingly, with considerations of the weather and required resources. Time is an important constraint that does not leave space for errors in the allocation of different types of professionals as the construction is time bound and generates additional cost if the date for completion is overdue. The learning curve opportunity is also missed in most cases because the workers change frequently.

Another distinction between the two fields is the more considerable amount of waste generated by the construction industry. Traditionally, waste can be defined as non-value adding activities for the final output, meaning activities that consume time, money, material resources and manpower and bring no value to the ultimate customer.

Although the focus usually lies on the material waste, Ohno described 7 types of waste. An overview is provided for understanding the full implications:

• Overproduction (unnecessary work): The production of a greater than necessary amount with the aim of building up the inventory or keeping the equipment running and attaining outstanding resource utilization. Done on a continuous basis, it causes quantity and quality problems, and it is difficult to identify without making a deliberate comparison between what is being produced and what is being sold and shipped. The usage of the mistake proofing approach and an extensive understanding of the production machines' capacities are recommended for addressing it.

• Time on hand/waiting (delays): Commonly described as idle time, it is easy to identify when the products are not being processed or moved, and it refers to the intervals spent waiting between processes/activities for different resources to become available. A possible solution is to create a sustainable flow.

• Inventories (storage waste): Stocking inventory causes monetary loss as the capital is being tied up and the space is occupied with materials susceptible to being inadequately stored on the site, deteriorated, stolen or vandalized. The issue stems from companies ordering more materials than required to fulfill an order as a direct result from an insufficient resource planning and/or uncertain quantity estimation.

• Transportation (materials movement): Mostly visible in the construction projects where resources need to be processed or moved inside of the construction site and it can be attributed in most of the cases to the layout of the working environment or to a lack of process flow, which results in multiple starts and stops in the transportation process and their correlated cost and waste of working hours, energy, space on the site. A method for addressing it is mapping a more optimized site layout.

• Movement: This type of waste stems from the way the resources and equipment are being placed around the site by the employees during the working hours which leads to more unnecessary motion, time and effort to perform tasks. The same inadequate site layout or the lacking work methods and insufficient equipment might be its root cause. An additional consequence is the increased rate of accidents and injuries and associated cost. Identifying and redesigning the jobs that produce this type of waste would reduce motion and cost.

• Over processing: It is described as additional processing of the product beyond the client's requirements which does not add further value from his perspective. A concrete example can be seen in the surface finishes. The waste of workforce potential falls under this category as well when the opportunity of making efficient use of their skills and knowledge is missed. Corrective measures consist of applying tools and methods such as the 5 whys and statistical process control or shifting the equipment used for construction.

• Defective products (unsatisfactory work): It occurs when final or intermediate products do not rise to the quality specifications and requires rework or the usage of poor quality materials. Reasons for which these rejects happen are numerous, some of them being improper integration between the design and production phases, loose planning and/or control, unqualified workforce. Mitigation directions include methods for their identification and removal such as the six sigma.

Lean construction

There are multiple perspectives in literature on what the Lean construction concept means, but this article will focus on the wide understanding that it is the application of the lean production principles and methods in the construction industry, with the Last Planner approach as a widely known example. Moreover, summarizing from the previous section, the two industries have different implications, therefore, a direct transfer of these principles is not possible without a considerable effort in changing the culture and management tools of the construction industry.

Similarly to Lean production, it promotes the timely delivery of projects, within the allocated budget and with the production of the demanded quantity and quality.