The commercial and residential building sector in the construction industry contributes to the generation of 39% of carbon dioxide emission and consumption of 70% of electricity per year in the United States (USGBC- U.S. Green Building Council). The USGBC was formed to promote and encourage the design and construction of green buildings in the U.S. as a necessity to resolve these issues for environmental, social and economic benefits. LEED (Leadership in Energy and Environmental Design) is a rating system developed by USGBC to help achieve sustainability by providing metrics against which credits can be earned by green buildings.
This rating program awards credits based on the level of sustainability attained by the building for certification. For a total of 110 credits, the four levels of certification are classified as: certified (40-49 credits), Silver (50-59 credits), Gold (60-79 credits) and Platinum (80-110 credits).
Sustainable buildings that are built through traditional processes often face delays, rework, overproduction and changes. This is caused because of the stakeholder’s lack of understanding and communication of the processes that are important for the delivery of the project.
Lean is a systemic approach to meeting a customer’s value. It maximizes value and minimizes waste by reducing variability in the process of the workflow. Lean can contribute to sustainability, but only if and when the customer specifies sustainability as a value. There are many researchers who report the positive impact of lean construction on the environment. The benefits include eliminating waste, preventing pollution and maximizing the owner’s value.
Lean and sustainability are complementary processes where sustainability focuses on improving the quality of the final product while lean improves the workflow of the process.
Their combined application can add value to the customer, enhance the improvement of the building and optimize resources. This research examines how lean tools and principles can be used to achieve credits for LEED v4 New Construction certification when sustainability is of value to the customer. The limitations of traditional project management in the construction industry led to the emergence of Lean construction. It is defined as a production management-based approach to project delivery (Lean Construction Institute). The concept of lean construction was adopted from Toyota’s Production System by James Womack who describes Lean as: “The most powerful tool available for creating value while eliminating waste in any organization”. He identifies the five key principles of lean as precisely specify the value of a customer, identify the value stream, make the value flow without interruptions, let the customer pull value from producer and pursue perfection by continuously improvising. According to Bae and Kim (2007), lean construction methods pursuing sustainability have:
Lean Tools used to reduce variability and improve workflow. The following lean tools were used in a case study that applied lean principles to improve sustainability of industrial waste management: Value Stream Mapping (VSM) is a tool that creates a detailed visualization of the process of material flow. It analyzes the inefficiencies and waste in each process and aims to instead add value to it. Pull system is a strategy used to reduce waste by enabling the production, based on the downstream customer’s needs. Unlike Push system, it delivers work to the customer only when there is a demand for it. The Kanban signal is a communication method which is a part of the Pull system. It is used to optimize inventory levels by alerting the upstream when there is a demand for the downstream.
The 5S method is a systematic approach to achieve organization, cleanliness and standardization in the workplace. 5S stands for sort, straighten, shine, standardize and sustain. Last Planner System (LPS) is a collaborative planning process designed to produce reliable and predictable work flow in projects. LPS principles include: Plan in greater detail as you get closer to doing the work Produce plans collaboratively with those who will do the work Reveal and remove constraints on planned tasks. Visual Control (VC) is any communication device used in the work environment that provides information to guide daily management actions. It helps organize planned work on site. Signals and signs are the most common examples.
Andon is a visual management tool that is used in Lean. It is a fundamental element of Toyota Production System’s quality control method, Jidoka. Whenever a worker detects a defect or problem in the production line, an Andon cord is pulled as a call for help to resolve the issue. Case Studies of Implementation of Lean Design and Construction for LEED Certification. Kristen Parrish (2012) studied the collaborative efforts between the stakeholders of a LEED Gold building using lean design for modular construction. The benefits that the modular construction brought to this project included deep energy savings, operational cost savings, and speedy delivery, apart from LEED credits earned. By evaluating several alternatives, the team was able to take energy efficiency measures by building models of estimated energy performances and propose a design that consumed 50 percent less energy versus LEED energy standard ASHRAE 90.1-2007.
Enhanced commissioning was proposed to track and monitor each building system’s energy consumption. The owner anticipates capturing all possible energy efficiency LEED credits with this level of energy savings. However, some miscommunication and lack of transparency between the teams, because they were not accustomed to the new working relationships, led to two problems- first, the assumption of upgraded costs between two project teams resulted in the selection of a mechanical system that was governed by the first cost rather than efficiency or value for the project. Secondly, roof monitors were installed in the wrong orientation because no assessments were made to check if drawings were updated after the discussion to change its direction. This could have been avoided if the modular contractor was present during discussions to plan orientation of the roof monitor.
Parrish suggests that informed decision-making would have been possible had all the stakeholders collaborated and communicated directly, and trusted each other to share their assumptions and costs. To achieve the sustainability of a building to its full extent, it is crucial for all project team members to clearly assign responsibilities and ensure that tasks are recorded and completed. She concludes that Lean theory offers solutions to these breakdowns. Similar conclusions were observed in the case study conducted of Toyota’s South Campus project, a LEED Gold certified building that employed lean processes. The environment was introduced as an additional customer and goals were set to meet its values: minimal building impact, maximum efficiency of the building systems and a healthy indoor environment. Programming was developed to identify goals and align sustainable features with the allocated budget.
Early selection of team members with sustainable experience, eco-charrettes, and alignment of team members and project goals played a critical role in the successful delivery of the sustainable project. Nahmens and Ikuma (2012) examined the environmental, economic and social impact of a lean tool called Kaizen on achieving sustainability in three case studies of modular houses. They observed that the hanging process of gypsum boards resulted in a reduction of material waste by 64 percent. Additionally, working hours for interior painting was reduced by 31 percent. Increased safety of workers and improvement of value added activities by 15 percent was also noted. There is a gap in the existing literature on this subject as most research papers report the benefits of triple bottom line (3 Ps of sustainability- people, planet and profit components) that result from combining lean and sustainability. However, there is no emphasis on specific LEED credits that can be achieved with the implementation of lean tools.
The case studies reviewed help draw out outcomes of the interaction of lean and sustainability principles. In conclusion, the greatest impact of implementing lean is seen in earning credits for the category of Energy and Atmosphere which has the highest score among the other criteria. Lean construction advocates that there is more value by integrating specialty trades into the project value stream. Early involvement of specialty contractors with experience in sustainable construction helps meet the project’s sustainability goals. It also has potential to earn credits for categories of Integrative process and Innovation in design. Prefabrication and modular construction help minimize waste by reducing the variability in work done onsite by taking the work offsite.
5S (a lean tool) assists in minimizing waste and reducing the variability of onsite work. Implementation of Kaizen has also shown to reduce material waste. These three systems can help earn credits for the LEED category of Material and Resources (Construction and Demolition- Waste Management). Collaborative Planning, a principle of Last Planner System, is synonymous with Eco-charrette, a requirement for LEED category of Integrative process. The case studies in the literature review show that the following credits have the potential to be earned with the implementation of Lean principles and tools in the building’s design and construction process: