View source for Just In Iime Delivery in Construction

== Towards JIT in Construction == 
The Purpose of JIT is to reduce cost by eliminating waste related to material storage, but also labor time and transportation.  There is a significant amount of value to gain by doing so, Hammerlund <ref name="art3">Hammarlund, Y & Rydén, R (1989), Effektivitetet i VVS-branschen, Arbetstidens utnytjande, (1989), Svenska Byggbranschens utvecklingsfond, Sweden.</ref> has previously shown that approximately a third of the time a worker spends on the building site, is regarding the procurement of materials needed by him, which adds up to ten percent of the total building cost. The optimum concept that JIT is, will only increase supply costs marginally compared to the magnitude of waste eliminated, thus increasing productivity <ref name="art4">Bertelsen, S. ; Nielsen, J. (1997). Just in time Logistics in the supply of building materials. 1st international Conference on Construction Industry Development: Building the future Together.</ref>. 
The waste in the construction industry is somewhat identified and the introduction of JIT can be justified. However, the application of JIT in the construction industry is substantially different to that of the manufacturing industry, due to their different types of production, and because of the greater complexity and uncertainty in construction. Construction is best conceived as a product development process.
The construction industry consists of building projects, that are scheduled driven. A smooth work flow and a high work performance is achieved if the schedule is kept. However, that is often not the case with specially large scale projects. Design modifications, slips in the deliveries, unforeseen complications and etc. are most likely to occur. The work flow can be shielded from some of these flow variations by keeping a inventory.
At the Toyota plant, Ohno successfully minimized inventories between any process, thus also reducing the safety stock that allows the continuity of a process downstream, should any deliver variation occur. What buffers are there in a construction project, that conceal variation and ensures a safety stocks, but also act as waste?

=== Construction Buffers === 
Ballard and Howell <ref name="art8">Ballard, G. & Howell, G. : Toward Construction JIT.</ref> defines two inventory types that might shield, or buffer, downstream construction processes from flow variations, together with suggestion rules for how to utilize them optimally.

-	'''Schedule buffers:''' ''Piles of stuff'': Materials, tools, equipment, manpower, etc. May originate in decisions to insert time intervals between scheduled activities. Act as added time to the project duration.

-	'''Plan buffers:''' Inventories of workable assignments, made by planning processes that make work ready for downstream production. Buffer by enabling a reliable and predictable flow output from a given process.

[[File:LH_Buffers.JPG|350px|thumb|right|'''Figure 1:''' Types of construction buffers .<ref name="art8">Ballard, G. & Howell, G. : Toward Construction JIT.</ref>.]]


In general, increasing the schedule buffers between supplier and construction, leads to an increased shielding from late deliveries, but does not address the cause to the problem of flow variation. This is obviously an expensive shielding application, both regarding time and money.
Thus, it is suggested to implement schedule buffers after processes with variable output. In general, fabrication and delivery can be considered to be very reliable and predictable, why the buffers with advantage should be placed between engineering and fabrication, instead of between fabrication and installation. This ensures that engineering completes its work correctly, increasing the chance that the design is final. However, this is obviously difficult to incorporate in fast-track projects. An additional rule states that schedule buffers should be sized to the degree of uncertainty and variation to be managed.
Plan buffers are required, and not to be replaced by schedule buffers. E.g. having a stock of an item, does not provide a working crew with workable assignments to install the items, and operate any transportation vehicle. At the site, assembling of components, determining optimum sequencing etc. is most optimal done before making assignments and committing to the work that will be done in the plan period (which is often one week, i.e. The Last Planner system). The plan buffers here determine what ‘can’ be done compared to what ‘should’ be done. Finally, the commitment to what ‘will’ be done, is governed by what ‘can’ be done. The future planning can now be improved by monitoring the PPC. 
Thus, if considering a construction process as a complex of work processes, a manager in charge of a downstream process can optimize piles of stuff he might have scheduled with, as shielding from unreliable inflow, if he has knowledge regarding the PPC of the previous process.

=== Strategy for JIT implementation in construction === 
JIT strives to eliminate physical buffers which is material inventories and time, and to obtain a one-piece flow within processes. This can be achieved at a production line, due to the high stability of the flow obtained by the production scheduling. However, such stability can not be obtained with construction scheduling, why it would be hazardous to simply remove all physical buffers, if the source of variation and uncertainty can not be eliminated. Ballard and Howell proposed the following strategies for the development and implementation of construction JIT, through the management of buffers.

''' Better location and sizing of schedule buffers: '''
Better assessment tools should be developed, to determine project uncertainties and the quantitative relationship between a buffer and the uncertainty they are intended to shield against. I.e. by improving the management of uncertainties and thus eliminating the causes of flow variation, physical buffers can be minimized.

''' Place plan buffers and make ready processes in front of each production processes: '''
The hypothesis is that production can indeed be shielded from upstream uncertainty through planning, why the use of the last planner system should be increased. Thus, the last planner method of detailed production planning shields production from uncertainties upstream. This will ideally result in the revelation of sources of variation and uncertainty which will enhance the productivity while releasing resources for further improvement of the performance of the process shielded, and provide a highly predictable work flow in the near-term to processes downstream.

''' Progressively replace schedule buffers with plan buffers: '''
The ultimate goal in the construction industry here is to obtain a predictability and reliability, so it can be totally independent of piles of stuff, and time between production processes.
The Hypothesis here is that work flow variations can indeed be reduced. If so, the following benefits will be implied. The buffer sizes can be reduced if flow variations are reduced. A reduction of these buffers between the event driven process chain (EPC) functions will yield a reduction of the total project duration. Furthermore, if work flow is more predictable, material, labor and other resources can be better matched at the right time to the work flow, and therefore increase the productivity. 
Thus, the implementation of plan buffers will propagate certainty throughout a given project.



Furthermore, the contractor can implement the following initiatives in the effort to overcome the problem of constantly dealing with unique projects instead of standard design projects, Pheng & Shang (2011) <ref name="art7">Sui Pheng, L. & Shang, G. (2011): The Application of the Just-In-Time Philosophy in the Chinese construction industry. Journal of construction in developing Countries.</ref>.
Training workshops and seminars for the development of better communication skills. - If engineers know more about the clients needs and expectations, rework can be avoided. Improving the build-ability of designs, by incorporating buildable principles (Poka Yoke). Implementing new integrated approaches for procurement such as D&B, instead of the traditional procurement processes, together with the establishment of supporting in-house design teams. The procurement process is indeed vital for the success of the JIT process. Procurement can be stabilized by ensuring long term supplier relationships. Thus, the following strategies are suggested: Develop a localized supply chain with few sources of supply. In the long run, the stability can be optimized by establishing partnerships with the best suppliers among them. Furthermore, long term relationships with subcontractors should be established, with a strict minimum quality level of acceptance.
In general, these are all initiatives that strives to stabilize the variations in the work-flow.

=== Benefits of JIT in construction ===

In addition to the previous discussed benefits of utilizing JIT, Pheng and Shang reports the following possible benefits <ref name="art7">Sui Pheng, L. & Shang, G. (2011): The Application of the Just-In-Time Philosophy in the Chinese construction industry. Journal of construction in developing Countries.</ref>:

-	Increasing the competitive advantage of firms in terms of consistently and continuously meeting costumer’s requirements.

-	Improving quality of construction materials and components

-	Increase in productivity.

-	Reduced costs due to minimized inventories

-	Improved relationship with supplier

-	Work completed ahead of time schedule

-	Improving the tidiness of the construction site

-	Elimination of site congestion and reduced inconvenience experienced by neighbors

However, these possible benefits can not be achieved without initial investments. For example, more advanced equipment and more skilled employees are required, if the setup time is to be reduced.

=== Barriers to the implementation of JIT === 

Several actors have failed in their efforts to successfully implement the JIT concept, due to a variety of problems. The implementation barriers encountered can be broadly classified into two categories <ref name="art7">Sui Pheng, L. & Shang, G. (2011): The Application of the Just-In-Time Philosophy in the Chinese construction industry. Journal of construction in developing Countries.</ref>:. The first is ''industry related problems'' which includes the limitations of building regulations, lack of certainty, inflexibility of JIT scheduling. The other category is ''human related problems'', which concerns the influence of stakeholders such as the contractor, subcontractors, suppliers and clients. Furthermore, is has been established that limited support from governments, consultants, clients and statutory boards does not promote the implementation of JIT <ref name="art7">Sui Pheng, L. & Shang, G. (2011): The Application of the Just-In-Time Philosophy in the Chinese construction industry. Journal of construction in developing Countries.</ref>:.