Hello again and welcome back to our course on Project 2013.
In this section we’re going to look at the critical path for a project.
So, first of all, what is the critical path of a project and why is it important?
The critical path is the set of tasks that must be completed for the project to be completed
on schedule.
Even with a project that’s not particularly big, there are usually some tasks that could
be delayed without affecting the overall end date or duration of a project.
But there’s also a set of tasks that can’t be delayed and that set of tasks is the critical
path and it’s normally a sequence of tasks that are from the beginning of the project
right through to the end of the project.
With virtually every project you deal with, it’ll be important to know what the critical
path is.
And the first thing we’re going to do in this section is to see how to identify the
critical path of a project.
Now what I’ve done is to add a few more details to our building project.
So I’ve added some subtasks under Lay foundation and some subtasks under Build walls and under
Fit roof.
So I’ve still got my five summary tasks but each of them now has a number of subtasks,
and if I expand each of those you see that the project is beginning to grow in size.
On the Gantt Chart Tools Format tab, one of the options is a checkbox in the Bar Styles
Group for critical tasks.
And if you click on this checkbox, you will show the critical tasks of the project in
red.
So click there are you can see that everything under Prepare site, everything under Lay foundation,
everything under Build walls, it’s all red which means they are all critical tasks.
If I go down to the bottom, everything under Fit roof is critical as well.
In fact, the only tasks that aren’t critical are the Fit windows and doors task.
Now in words the reason for that is that in effect Fit windows and doors happens in parallel
according to this schedule with the task of fitting the roof and because the fitting a
roof task takes longer, the fitting doors and fitting windows task could take a little
longer than we intend without having the overall project delayed.
Now, of course, at this stage I’m still looking at a version of this schedule where
I have resource overallocation issues.
And if I now level the resource, let’s see if my critical path changes.
So I’m going to go to the Resource tab.
I’m going to say Level all.
It levels the tasks for the carpenter who was the only overallocated resource and those
tasks are still blue.
So the red tasks, the ones that were critical are still critical and the blue tasks, the
ones that were noncritical are still noncritical.
Now it’s very important to know at any time when you’re working on a project which the
critical path and which the critical tasks are because they’re the ones that you must
complete on schedule in order for the project to finish on the currently planned finish
date, whereas for the noncritical tasks such as ground floor doors here, we’ve got what
is called slack.
We can actually have a certain amount of delay on that task without delaying the overall
project.
And it’s slack that we’re going to look at next.
Now again if I go to the Gantt Chart Tools Format tab and look in that Bar Styles Group,
there is a checkbox there which can show a line to represent slack in a task.
Now let’s enable slack in this view.
For each of the critical tasks, the red ones, there is no slack.
But if you look at say this blue ground floor doors task here, you can see a little line
coming out of the bottom of it.
That line denotes the slack.
And basically all four of those blue tasks have slack that takes them up to a deadline;
effectively it’s the deadline that would correspond to the point that the roof is finished.
So right up to the time that the finishing of the roof is done which on the current schedule
is the end of the building of the house, those could be delayed right up until then without
affecting the end date.
So we’re basically working on the principle that, say, in the case of ground floor doors,
there’s quite a lot of slack available there.
And in the case of this one, ground floor windows, quite a bit of slack as well, the
others have less slack.
Now apart from showing slack like this on the Gantt Chart, don’t forget you can always
show in the table that sort of property of a task.
So let me just right click here on task work, do insert column.
Let me just scroll down here and one of the fields is Finish slack.
And you can see what the finish slack is for each of my noncritical tasks, how much the
finish of that task could be delayed by without delaying the overall finish of the project.
So, again, a very useful way to use the ability to customize the shown table to show the numbers
that correspond to the bars in the bar chart there, in the Gantt Chart, that show the available
slack in each of those noncritical tasks.
Now if you have a very big project, it can be quite difficult to see all of the critical
path in view at once and you may have odd critical tasks all over the project.
Apart from the ability to flag the critical task by showing them red as we did here, another
thing you can do is to use a filter in the Gantt Chart.
And in fact filtering in general in a Gantt Chart is a pretty useful thing to be able
to do.
So what I’m going to do here is just switch off the slack in the Gantt Chart for the moment,
and what I’m going to do is to go to the View tab and in the View tab one of the groups
there is the Data Group.
We already looked at tables in the Data Group, but we also have here the ability to filter.
Now at the moment, no filter is applied but if I want to just show specific tasks in this
Gantt Chart, I can apply one of the standard filters.
Click on the drop down to the right there for a standard filter and one of the standard
filters is critical.
Amongst the other filters we have tasks that are active, ones that are in progress at the
moment, tasks that are complete, tasks that are not completed, ones that are currently
running late, milestones, summary tasks, a number of others, and you can actually create
filters of your own.
But at the moment, we’re just going to look at critical and we’ll be dealing with one
or two of those other filters later on.
So let’s just show the critical tasks.
Now what that then means is that we lose the noncritical tasks and we can identify just
the critical ones and you can see the sequence of those through the life of this project.
So although I only have some of the tasks for the house building project here, I’ve
got enough really to talk about the fundamental work that we’re going to do over the next
few sections of the course.
Typically in a situation with a project like this one, one of our objectives will be to
shorten the critical path.
We currently start work on a certain date.
Let’s bring up the timeline which will tell us that currently we start on April 2nd and
we finish on June 5th, and one of the requirements we may be given is we want to finish that
by the end of May.
Now how can I shorten a critical path?
Shortening the critical path is something that a project manager will do quite a lot
when they’re using Microsoft Project.
Now there are a few basic possibilities but if we start at the very highest level of possibilities
given the critical path as it is now, you can either shorten some of these tasks, so
a task like demolition five days.
Could I do it in four days?
A task like footings and slabs three days.
Could I do in two days?
And so on.
And by reducing the duration of the tasks, I can reduce the length of the critical path
or I can change the relationships between the tasks.
Generally speaking, at the moment none of these critical tasks overlap each other.
But is the process of building this house such that some of these could overlap each
other?
Could I start building the upper floor walls before I finish the ground floor walls?
Some of these questions are sort of theoretical questions in a way and you might well say
well, how can you possibly start building the upper floor walls before you finish the
ground floor walls?
And some of them may be a combination of theoretical and practical in that you might say well in
fact, you could but what if you’ve only got one brick layer?
He can’t do both.
So maybe your resources will constrain what you can do anyway, and it’s very difficult
to generalize about what can and what cannot be overlapped.
But if we look at this particular building project which is what we’re going to do
a little bit later on, we can look at specific tasks within it and based on what needs to
be done and based on the resources that we have available, we can look at opportunities
to overlap some of the tasks.
So we’ve got making the tasks shorter and we’ve got overlapping the tasks.
Now when we talk about making tasks shorter, it isn’t only about reducing the amount
of work.
It’s often more about reducing the elapsed time for tasks.
So it might be five days work but could we do five days work in three days?
And then we look at options like what about working overtime?
So in each of these situations there are very practical considerations and there’s usually
at least two or three different approaches to achieve a specific objective.
So having identified the critical path in our project, now let’s start looking at
some of the ways that we can reduce this critical path.
Before we do that though, we need to look at a very special kind of task which is a
milestone and that’s what we’re going to look at in the next section so I’ll see
you then.