Enter the Matrix… of Construction Scheduling

One of the most detrimental technological “advancements” to ever impact the construction industry was the mass adoption of Gantt charts during the 1980s when MS Project became part of Microsoft’s Office Suite. Gantt charts are most useful in project planning where several lines of project work with highly variable individual project steps ultimately come together for a final product where a critical path might be “managed” between various results. Construction, by and large, has no need for so sophisticated of a tool. Aside from being the wrong tool for schedule management even for those well versed in its use, most field personnel will take one look at a chart like this and throw it in the bin.

The Toyota Way

Many in the development industry have heard of the concept of “lean construction,” however, few have any real understanding of what it means, often thinking it is just some industry term for greater efficiency. Lean Construction has its roots in Japanese manufacturing techniques (now employed by every manufacturer) that enabled them to dominate US manufacturing in the 1980s. While there are 14 principles within the Toyota Way and we will delve into the others in a separate article, the primary intuitive concept we can apply is that of Pull Planning. What is that? When Taiichi Ohno, who developed and instituted many of these now lauded principles, visited a US grocery store, he was fascinated with the way a typical store manages its inventory. Inventory, in too great a quantity is wasteful and in too little halts production or sales. The best way to think of this is the beverage aisle. Beverages can have relatively short expiration times (e.g. milk) and cannot be inventoried in great quantities lest it spoil. How does one stock a shelf to ensure the oldest beverages sell first? Beverage aisles often load from the back, so that the older containers are at the front facing the customer. How does the person stocking from the back know what inventory has moved and must be replaced? He merely looks at a given row and sees on has only one container remaining at the front while another one has three. He then adds more containers to the one with fewer in inventory, thus automatically ensuring the right amount of inventory is kept in stock.

What does any of this have to do with construction scheduling?

Much like the fixed rows of a beverage shelf, construction operations must occur in a particular sequence. This sequence of events is dependent upon the prior activity and no work can proceed until the prior activity is completed. Generally, there are between 25 and 30 independent trades who make up these individual steps in the process. This is why Gantt charts are ineffective for construction scheduling, because there is no way to manipulate the schedule and find some undiscovered critical path sequence that will magically complete the project sooner. The plumber can only start their rough in once framing is complete. The drywaller cannot start until all rough in and insulation is complete. The fixtures cannot be completed until tile and countertops are complete. Therefore, each trade must be scheduled to take the same amount of time in each work area. Let’s use the floor plan below to illustrate this concept.

First, let us assume that not every trade has unlimited workers that can be thrown onto a job at the whim of the general contractor. Therefore, there is some limit to the resources available and, thus, how much work a given subcontractor can complete in one work week (we will explain more later about why the work week is the correct increment of time around which to organize a schedule). Let us assume that after discussion with the subcontractors it is revealed that the plumbing subcontractors assumed he would provide a three man crew for the length of the project and that three man crew can complete one of the four areas indicated above within a work week (in reality, this is more likely to be a back and forth discussion between the general contractor and all of their subcontractors, but for this example it establishes our bottleneck). Why is establishing a bottleneck important? Because no matter how fast any other single subcontractor can operate, the project cannot be completed any faster than the bottleneck can accomplish their work. Why does this matter?

Assume the general contractor does not design their schedule around an understanding of a bottleneck. The framer tells the superintendent, “I can throw 100 guys on your project and have it all framed in a few days.” This sounds great to the superintendent, so he lets them descend upon the job site like a flock of locusts. The following week, the framers have vanished, and the plumber starts to work on their rough in. However, they can only do so much work within a week, meaning that every subsequent trade must wait for them to clear an area, thus giving no tangible advantage to the overall schedule. (The schedule could only be compressed if every trade could man up in the same manner, but recall we have already established that bottlenecks exist, whether we want them to or not). In addition, as the plumber moves into new areas, they discover that not all the framing was done correctly to allow for their pipes, and certain sections must be reworked. Not only is it difficult for the superintendent to get the framers back to correct this work (having moved on to another project) but also every error in framing at every identical condition (of which there are many as most modern designs involve a lot of repetition) must be corrected after the fact rather than the error having been discovered earlier so that it would not be repeated. Not only that, but because the framer completed their work, all that work in place will be invoiced on the pay application and begin accruing construction interest while the work sits idle waiting for the subsequent trades to catch up. How is this advantageous to anyone.

Not only is it more important to sequence the work being mindful of the bottleneck, but it makes the schedule far easier for anyone to follow. While the commercial construction industry tends to look down upon the homebuilding industry, because in their estimation homebuilding construction is not as complex or sophisticated as commercial construction, the homebuilders have continued to utilize a simple sequential schedule from their inception in the 1800s. It is the commercial general contractors who moved away from sequential scheduling for the seeming sophistication of Gantt charts. This is how the largest office building in the world, the Pentagon, was completed in a mere 16 months when no general contractor could do the same today.

For example, this is an actual schedule used by a top tier national homebuilder and continues to be in use today. It is exceedingly clear which trade needs to be working on this home in any given week and wat work must be accomplished before the next sequence of work can begin.

But how does one extrapolate this for larger commercial buildings?

This is also exceedingly simple. By creating a matrix schedule, where the columns are defined as above by the sequence of work, and the rows are determined by a predefined area and floor of the project. If there are multiple buildings in a project, this too would be defined by row. Additionally, a simple color coding will enable any observer to see what work is complete, in progress or not yet started. One of our general contractor partners developed this methodology specifically for commercial construction. We highly recommend the utilization of their methodology and technology in lieu of Gantt charts or other scheduling methods. An example of their product is below for illustrative purposes and more information can be found at clearflowmatrix.com.

This methodology has the added benefit of enabling the user to visually look at the diagonal “balanced work front” to identify what areas might be behind and further bottlenecking the schedule. For instance, in the example below, the drywaller has fallen behind in the kitchen/dining area of this medical office building.

We mentioned earlier why the work week is the ideal time increment around which to base this type of schedule. This is for two reasons. First, it is the natural way in which we all tend to work, establishing at the start of a given week the goals and assessing at the end of the week if they have been accomplished. Second, the more consistent one can make the tasks for subcontractors week after week, the more efficient they become and the more quality improves. This in turn can have downstream effects. For instance, if a developer has a second phase or a near identical project (as is common with a prototypical design) slated to break ground in the near future, a subcontractor will likely recognize that they could bid even more competitively on the next project and still make a profit (by, for instance, now seeing that they might not need as large of a crew to perform the same amount of work within the time required). Third, part of the Clear Flow Matrix process also involves engaging subcontractor foremen to walk (typically on Thursday) the areas immediately preceding their work for the subsequent week to ensure it will be ready for them. This establishes a self-policing culture on site and, when implemented properly, assures the superintendent is made aware of any shortcomings by one trade or another. This in turn enables them to enforce weekend or overtime work to ensure any trade which is behind completes their work before the start of the next week.

Isn’t this Means and Methods? How can I force my General Contractor to change their schedule?

We do not believe this is about forcing a general contractor to do anything. Certainly, the first step would be to discuss this approach with them early in the preconstruction process. It is possible, though perhaps unlikely, they may be open to learning and employing a different method. That said, we will not sugar coat that general contractors are often stubborn and resistant to change. What we can say is that the general contractor who developed the Clear Flow Matrix methodology which they implement for their own projects had a track record for outstanding schedule performance. An alternative approach would be to require by contract that a schedule using this methodology be produced and submitted by the general contractor to the developer/owner’s representative (ideally weekly). The standard AIA contracts require that the general contractor produce an updated schedule for the OAC meeting. There is no reason that the developer cannot require it be in this format rather than a Gantt chart. At a minimum, this will make it far earlier for the owner’s representative to truly understand the status of the work, whether or not the project remains on schedule and/or identify any potential bottlenecks which might need to be addressed.

For those developers who have decided to take the plunge into internalizing construction, there is no better time to implement a scheduling standard than as the team is being built and processes and procedures are developed. Unfortunately, developers often must staff this new department with external hires who, coming from general contractors, will be similarly wary of implementing a schedule methodology with which they are unfamiliar. All we can do is express that this methodology is best practice, proven and once implemented, far easier to understand and explain to individuals outside of construction.

We do not anticipate Gantt charts being abandoned by the construction industry anytime soon, but we know that with greater exposure, Clear Flow Matrix type scheduling will result in greater success and thus become more common over time.