I will preface my comments and say we are all at different stages in our LeanTakt journey in the construction industry; and the fact that the US market is still clinging to the CPM tools of yesteryear makes this question problematic to answer generally. So I am choosing to refer my comments mainly for the US market even though we have a broad coalition of international leanTakt folks that might disagree with some of my generalities. (for instance in Germany over 50% of construction projects are planned and executed using Takt, according to experts from the region).
The sooner we can understand (and help our clients understand) that we will encounter variation on our projects; the better off we will be. Because we will encounter and have to deal with variation on every single project that we will ever be a part of.
In the amazing book The Goal (which is a must read for everyone in construction!). The Author Eli Goldratt wrote about an issue that is near impossible to predict 100% but needs to be accounted for. He called this Statistical Fluctuation because of this what I call “variation”the straight production math does not work out. Mike Tyson’s famous quote applies here: “everyone has a plan until they get punched in the face”.
in the book Alex Bogo (main character) also figured out that only a few processes in his manufacturing plant need to be working at a high utilization or capacity. These are the systems bottlenecks. Again if you have yet to read this book you are missing out on why construction production has been stagnating for decades (see chart Below).
So when planning and you are new to takt planning the easy thing to remember is what Katherine said, we know about this and need to account for it….. But hold on I have some great value on a process on how to do this today right now that will help you even if you have not found a way to capture either the variation or utilization. It is called work packaging and buffer management.
When you know your sequential work flow in a production area that I would call a takt zone
from say a phase pull plan (see Last Planner® System)
you now have the opportunity to systematize your production line into Takt wagons that are aligned to your bottlenecks production, the rule of thumb we follow when doing this is that the Takt time should be aligned with the bottleneck in some form (there are various ways of doing this). Next you “package” the work packages (the individual sticky notes from the pull plan) together into groups that can be in the same zone at the same time. These are called Takt Wagons.
You will add in integrated buffer to account for some of these effects mostly for the non bottleneck work packages. For the bottlenecks we use Buffer Management in the next section. Again this is where you would theoretically just add in some buffer to account for our variation and utilization.
T is identified primarily from the phase pull plan above
V&U are accounted for with work-packaging and buffer management
From the Optimization step you will usually find time you can save with changing batch sizes and limiting work in process (WIP). From that time saved it allows you the ability to add the needed buffer into the plan to achieve flow. This is what CPM doesn’t do for us, since its primary focus is resource efficiency it inadvertently has us max our utilization of resources all as much as we can which just creates busy people working on a ton of non value add stuff and increases WIP elongating our overall duration.
Just like the image above a freeway with 100% utilization is a parking lot! So obviously adding in the buffer makes sense because the likelihood of everything going to plan with no variation is 0% meaning we have to have it in our plan and understand where it is. Either just the CPM expert knows where this is or its thrown in as larger activity durations and weird logic ties that end up making the plan not useful in the first place.
So when bottleneck has been established and is driving your takt time there are a myriad of ways to add in “visible” buffer. These buffers should account for two things, if we understand that the bottleneck is going to be the most utilized resource then we need to allow it some buffer so it is not planned at 100% utilization. It is also added in to account for variation that will occur just like was mentioned above.
5% integrated buffer for non bottleneck work packages
use the remaining buffer to systemically support the bottleneck
Use Stability Parametric to know if you have the right Bottleneck buffers vs calculated end buffers.
I am sure there might be more questions and It also happens that we cover these topics in our upcoming class on Takt in construction and we only have a few more spots open so jump in and sign up if you are interested. (Click Here)
The best way to identify your variation and account for it in your work packages is to track this with your roadblock tracking maps and gather data on variation that you caught ahead of time. Also if you are using the Last Planner® System and are tracking PPC & Variances this is the data on items you didn’t resolve and did effect you. With This information you can calculate how much variation you should encounter. It is different for each type of work in construction (health care, industrial, high rise). Thus tracking and accounting for it will be at the company or department level. When you have tracked this historical variation you can use that as a percentage for integrated buffer in work packaging and buffer management.
Here is a video where tracking historical information can help you with planning the same work in the future because the sequence.