Masterbuilder lean sawhney_october2011

Cover Story Lean Construction

MODELLING VALUE IN CONSTRUCTION
PROCESSES USING VALUE
STREAM MAPPING

Anil Sawhney, PhD FRICS
Professor, Department of Civil Engineering,
Indian Institute of Technology Delhi, Adjunct Professor,
School of Built Environment, University of Technology Sydney

Value, especially the way it is perceived by the user, should principles, the construction industry is embracing these
be used as a driver for the design and construction of our principles by reincarnating (adapting and adopting) and
built environment. Paying attention to value should be of enhancing them as "lean construction". Aptly stated, lean
paramount importance to all the stakeholders involved in construction is "the quest for synchronized and continuous
the project delivery process. The industry, however, improvements in design, procurement, construction,
struggles with honing its focus on value. This has led to operations and maintenance processes to deliver value
an estimated 20% decline in productivity compared to to the entire project delivery network".
other industries and approximately 30% waste in
Implementing lean principles in an organization can be a
processes and delivery methods (Gallaher et al 2004 ).
challenging task. A number of approaches, tools and
Traditionally, project participants construe projects as a strategies are used in lean implementation. Value Stream
connected network of activities that can be controlled Mapping (VSM) is arguably a powerful mapping tool that
and improved individually through a structured set of can be used by an organization in their lean
management techniques, leading to successful implementation journey. In a workbook entitled "Learning
management and delivery of the overall project. to See-value-stream mapping to create value and
Deficiencies in the models and theory behind "task- eliminate muda" authors Mike Rother and John Shook
oriented" project planning have been debated extensively provide a well-rounded elucidation of VSM . VSM has
by experts who have particularly pointed out the difficulties become one of the commonly used tools to implement
in managing uncertainty in the workflow and lack of focus lean principles (Lian and Landeghem 2002 ); as it
on "handoffs" between tasks. A second school of thought provides a simple map to see and understand flow of
has emerged recently in which construction projects are materials and flow of information in any process (or group
envisioned as a series of work processes with an equal of processes). VSM has its roots in Toyota's material and
emphasis placed on the processes and the connections information flow diagram and as such has a manufacturing
between them. This view has come to be known as twist. Jones and Womack (2000 ) define VSM as a "process
"production planning". Numerous studies in this area of observing the material and information flow as they
resulted in the conceptualization and formalization of this occur now, summarizing them visually and envisioning a
view and have led to the growth of the lean construction future state with much better performance".
philosophy (Koskela et al. 2002 ). Lean thinking, with its The basic objective of developing a VSM is to establish
roots in the Toyota Production System (TPS), revolves the flow of material, information and people; eliminate
around the bedrock principles of "continuous waste; and add value to the end product. VSM provides a
improvement (kaizen)" and "respect for people". Using the systematic visual representation of processes, value
"challenge everything" and "embrace change" mind-set, added and non-value added steps, lead times and
an organization can systematically adopt the lean inventories in the delivery of products (and projects). It
principles in their core business processes. Waste provides holistic visual map of the production processes
elimination and tools surrounding waste elimination to or supply chain network diffusing the implementation of
some extent are a shallower view of lean as lean principles lean concepts at the organization level (Rother and Shook
run much deeper. Understanding the importance of lean 1999).

88 The Masterbuilder - October 2011 • www.masterbuilder.co.in


Figure 1: VSM Symbols in Microsoft Visio

The proponents of VSM call it a paper and pencil tool that contribution of all stakeholders involved in the process
makes use of icons or symbols to represent commonly with the help of a lean implementation expert. Figure 3
occurring steps in a production process. Due to its shows the current state VSM for the concrete foundation
manufacturing roots, most of these icons have a process for a concreting subcontractor involved in the
production slant. A number of software tools are now construction of detached residential units . Information
available to assist the development of VSM. Figure 1 flow from customers, information flow from the company's
shows the palette of icons available in Microsoft Visio to central scheduling office, material flow from suppliers and
assist in the development of VSM. other VSM related components are captured in the current
state map. Activities including layout, set perimeter form,
Using these symbols, maps of both current state and future place soil pipes, grade, set post-tension slab and pour
state of any construction process can be created. slab concrete are all shown in the VSM. Their cycle times,
Experience and expertise is needed to develop these inventories, non-value adding times and other process
maps, especially the future state map. Identifying waste related information are also captured.
and non-value adding activities and removing them by
using lean principle leads to successful implementation Future state process map refers to an improved version of
of VSM. the current state process map. Development of future state
map involves analysis of current state, identification of
Additional icons can be added to the above set to suit wastes and minimization or elimination of wastes. Future
the needs of the industry and the organization for which state process maps are developed based on the analysis
the map is being created. VSM, especially the manual of the current state using lean production principles.
approach, can become cumbersome as the level of detail Development of future state process map requires
increases. The key obstacle to this mapping exercise in identification of wastes in the current state. Wastes can
construction is the task-orientation and the mind-set that be any one of the following: waiting time, over production,
is common in the industry. Modelling real world scenarios excessive inventories, defects, inappropriate processing,
in construction often involves many value streams and unnecessary movement of people or unnecessary
consisting of multiple products and parts requiring careful transport of goods (Ohno 1988 ).
planning. VSM provides a static model either at current
state or future state. It does not capture the dynamic In the concrete foundation example, once the current state
behaviour of production processes, for example it is not map is completed and data is collected from the
possible to observe the variation in the inventory levels construction site, the project team can start the
with respect to time for different scenarios (Lian and development of the future state map. The first
Landeghem 2002 ). VSM is mostly applied for systems consideration in this example is given to the perimeter
characterized by linear product routings. Often real world activity, which is completed in one day, but the handoff to
scenarios in construction involve nonlinear, non-identical the soils activity causes a non-value added time (NVAT)
product routings that flow and merge at multiple levels. of 12 hours. This can be reduced to 4 hours by efficient
Notwithstanding these issues, VSM remains a useful tool scheduling and handoff to the plumbing subcontractor.
in the arsenal of a construction company embarking upon This will reduce the cycle time of perimeter activity from 2
the implementation of lean principles. days to 1 day. Since the value added time of the perimeter
activity remains unchanged; the proposed improvement
Repetitive construction processes can be the first easy will not exert any additional production pressure on the
target in the lean journey of a construction company. VSM perimeter crew. The second activity that accounts for
for these repetitive processes can be developed via the waste is the place soils pipe. Due to poor inspection pass

www.masterbuilder.co.in • The Masterbuilder - October 2011 89


Figure 2: Current State VSM of Concrete Foundation Process

rate, the quantum of rework is high leading to high rework due to limited resource availability, inspection failures or
and NVAT. There is potential to reduce the NVAT of this reworks and delays due to poor coordination among
activity from 16 hours to 8 hours if rework is minimized. subcontractors during handoffs. While the presence of
The NVAT of set activities can similarly be reduced from excessive inventories increase the waiting time and the
18 hours to 10 hours. These improvements are shown in overall lead time, a scenario of no inventory makes the
Figure 5. downstream activities vulnerable to the workflow variability
of the upstream activities. A balanced inventory size
Further improvements to the process can be made. Data needs to be identified so that there is sufficient buffer
collected from the project shows that the inventory between any two activities with an acceptable amount of
(expressed in terms of number of residential units under increase in the lead time. This second future state is
construction) is 10, 24, 23, 16, 16, and 13 before activities developed by maintaining a constant inventory size of 10
'layout', 'set perimeter', 'place soil pipes', 'grade', 'set PT before each activity. The inventory lead time before each
slab' and 'pour floor' respectively. Uneven and excessive process becomes constant and it is equal to 8 hrs. The
inventory causes waste in the process. This is caused by value stream process map for this future state is shown in
bottlenecks in any one of the six construction activities Figure 7.

Figure 3: Future State Map for Scenario 1





Future state-3 is developed considering the layout and stream map of the future state-3 is shown in Figure 9.
perimeter activities. The value added times for layout and The simple VSM (current state and 3 future state maps)
perimeter are 1.5 hours and 4 hours respectively with a maps show the use of this tool in modelling value in the
non-value added time of 6.5 hours and 4 hours construction process. Using input from all the team
respectively. This primarily occurs due to limitations in members, improvement in the process cycle efficiency
the scheduling system. The 90 minutes activity is can be achieved via VSM by reducing waste. Table 1
scheduled over an 8 hour period as the deployment of illustrates the improvements accomplished via the use of
the layout and subsequent deployment of the perimeter VSM.
crew cannot be tightly controlled with the scheduling
system. With some enhancements in this system, the layout Reference
crew and the perimeter crew can be assigned on the - Gallaher, M., O'Connor, A., Dettbarn, J., and Gilday, L. 2004.
same day for each unit leading to the combination of the Cost analysis of inadequate interoperability in the U.S. capital
two activities namely 'layout' and 'perimeter' into one facilities industry, United States Department of Commerce
activity. This reduces the cycle time by one day and Technology Administration, National Institute of Standards and
eliminates one inventory holding location in the process. Technology.
The combined non value added time reduces from 10.5 - Koskela, L., Howell, G., Ballard, G., and Tommelein, I. (2002).
hours (future state-2) to 2.5 hours (future state-3). The value "The Foundations of Lean Construction." Design and
Construction: Building in Value, R. Best, and G. de Valence,
S. Variable Current Future Future Future eds., Butterworth-Heinemann, Elsevier, Oxford, UK.
No. State State-1 State-2 State-3
- Rother, M. and Shook, J. (1999) Learning to See: Value Stream
1 Total Cycle Time (CT) 128 hours 104 hours 104 hours 96 hours
Mapping to Create Value and Eliminate Muda, Lean Enterprise
(16 days) (13 days) (13 days) (12 days)
Institute.
2 Total Value Added 62.5 62.5 62.5 62.5
Time (hours) - Lian, Y.H. and Landeghem, H.V. (2002) An application of
3 Total Non-Value Added 65.5 41.5 41.5 33.5 simulation and value stream mapping in lean manufacturing,
Time (hours) Proceedings 14th European Simulation Symposium, A.
4 102 60 Verbraeck, W. Krug, Eds.
Total Inventory Size 102 50
(number of residential - Jones, D. and Womack, J. (2002) Seeing the whole: Mapping
units) the extended value stream, Lean Enterprise Institute, MA.
5 Total Lead Time 81.6 81.6 48 40 - Lian, Y.H. and Landeghem, H.V. (2002) An application of
equivalent to the
simulation and value stream mapping in lean manufacturing,
Inventory Size (I-LT)
Proceedings 14th European Simulation Symposium, A.
(hours)
Verbraeck, W. Krug, Eds.
6 Total Lead Time 209.6 185.6 152 136
(CT + I-LT) (hours) (26.2 days) (23.2days) (19 days) (17 days) - Pramod Tipparaju and Anil Sawhney (2006) "Value Stream
7 Process Cycle 29.82 33.67 41.12 45.96 Mapping in Homebuilding", Technical Report, Arizona State
Efficiency (PCE) (%) University
- Ohno, T. (1988) Toyota Production System: Beyond Large Scale
Table 1: Summary of Improvements Production, Productivity Press, Cambridge, MA


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