The critical path: Just how critical
You’ve probably heard the term “critical path”
many times. But what does it really mean and how can it
help or hurt you when it comes to delay claims on a project?
The standard nearly all courts recognize what is known as
the Critical Path Method (“CPM”) as the most
readily accepted method of measuring project delays. CPM
is the benchmark that is universally accepted in construction
delay claims litigation.
It is extremely important for anyone
involved in construction to understand how CPM is used for
proving delay claims. If you don’t know how a delay
is measured, you may find it difficult proving you were
really damaged by a delay. Or worse yet, you may find it
difficult defending yourself against an unfair delay claim.
A quick history Commonly known by its initials “CPM,”
it is a method of estimating how long a project will take
to complete. A critical path is determined by taking the
key tasks in sequence and adding up the longest time necessary
to complete all the tasks to determine the project’s
total length. The procedures are the same for small projects
or large projects, but larger projects will benefit from
the use of project management software, since the software
can handle hundreds of tasks and variables with ease.
project management software uses a variant of CPM called
PERT, which means Program Evaluation Review Technique. PERT
was developed in 1958, a year after CPM was first used,
but the name CPM has become synonymous with both methods.
What distinguishes PERT from pure CPM is its use of statistics
to predict completion times. Using three time estimates,
optimistic, pessimistic and most likely, a more realistic
completion time estimate is created.
The basics here is
a quick primer on what it takes to create a CPM schedule.
CPM is focused both on time and sequencing. First, a sequence
of work is determined. Then, assign each sequence a time
interval required to complete it and theoretically you have
a critical path. You need to know the following information
in order to create any sort of CPM schedule:
1. Specific activities: These are unique tasks that have
a distinct length of time for completion. In construction,
these are usually straightforward and fairly easy to identify
2. Milestones: These are events that
identify the beginning or end of a task.
3. Sequence: Getting from bare
earth to a finished building requires
the proper sequence of construction
tasks. Some sequences are obvious,
and others are not. For example, it is
clear that earthwork must come before
roofing. But, it may not be so obvious
whether finishing the plumbing would
come before or after roofing, or
whether it really matters.
4. Dependent tasks: Careful analysis is
often needed to determine the cause and
effect relationships between tasks. Tasks
that depend on the completion of another
task must be identified.
5. Time estimate: The time required
for each activity is needed. An experienced
estimator can shoot from the hip
and use past experience as his guide,
but often input from each trade is
needed to get realistic estimates of time
for their work. It is at this point that
PERT-type statistics would come into
play (whether calculated manually, or
generated by project management software)
in order to arrive at the best estimate<
for a task time.
With the above information available,
a project diagram can be created. Laid
out graphically, all the milestones
(events) are connected together by a network
of activities (tasks) to visualize the
entire project from beginning to end.
The critical path would be the longest
duration of tasks that must be done in
sequence in order to get from the
beginning to the end. There may be
tasks that can be performed in parallel
with other tasks.
There may be tasks that can be performed
at any time after achieving a certain
milestone but have no specific start
date, only a required completion date.
The difference between the time allocated
to perform the task and duration
of the task is commonly known as float
or slack time. All tasks on the critical
path have no slack time.
The real world-
Once a project is planned out and a
critical path defined, there is no guarantee
that the course of the project will
actually follow the plan. A few examples
of why this can happen are:
• Estimates: One of the simple reasons for a schedule
deviation is that everything is based on estimates. The
schedule is only as good as the quality of the estimates,
and for the most part, the people who created the estimates
are not the people who actually perform the work.
• Changed conditions: If actual conditions are different
from those expected at the time estimates were determined,
those estimates may not be realistic.
• Change orders: Almost without exception, projects
will have change orders. What needs to be considered very
carefully is whether or not the change orders affect just
a specific task schedule or the critical path.
Making CPM work for you- Keep in mind though, that just
because there may be change orders, changed conditions,
sloppy estimating or anything else that causes a delay,
if the delays do not affect any of the critical path tasks,
the project as a whole, is not delayed.
Also, applying additional resources
to activities that are not on the critical
path may allow them to be completed
early, but it won’t benefit the overall
project end date.
Remember, improving the estimated
completion date, or getting a project
back on track to finish by the promised
date, depends on your ability to identify
and shorten the tasks or activities that
are on the critical path.
If you have a construction question, submit it to: info@construction-laws.
• • •
Disclaimer The information in this article is based upon
California law and is for general information only. Any
information or analysis presented here is intended solely
to inform and educate the reader on general issues. Nothing
presented or referenced to, regarding facts, documents or
applicable laws, constitutes legal advice. Before acting
or relying on any information, including any information
presented here, consult with a qualified attorney for your
Scholefield, Esq., holds an active PE license in Colorado,
an undergraduate engineering degree from the University
of Florida, and received her JD from the University of San
Diego. Source Code: 20080314tca
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