Reference: http://www.projectengineer.
net/steps-in-project-scheduling/
Task Length
There is no universal correct length to a task, but if you have more than 10 tasks per phase it
becomes difficult to manage and a third (or fourth) level should be created. A common yardstick
is the 8/80 rule, which states that a task should be between 8 and 80 man-hours. Shorter than
this will aggravate your project team as you micromanagement their daily work, and longer than
this makes it difficult to accurately assign completion progress.
Estimate Activity Durations
Just because a resource is necessary doesn’t mean it’s available. To determine the availability
of resources, a project manager consults a document called a resource calendar. This document
states the availability of a resource, for example, “Mark is at jobsite X from Sep. 1 to Sep. 30.”
Obviously, the new project being planned cannot use this worker at that time (unless
arrangements are made with the other project manager, I suppose).
Estimating is a profession in itself, but there are three methods you can utilize to determine
activity durations:
Analogous Estimating: In this method you consult the actual data from a previous or
related project. Even if it has some differences to the current project, you can analyze those
differences and apply a correction factor.
Parametric Estimating: In this method you break down the project into its fundamental
units that have well known and understood unit rates. For example, the square footage of a
house.
Three Point Estimating: When you have no real good data to go from, you can
estimate the highest possible number (optimistic), and the lowest (pessimistic) as well as
the most likely. Then you can use a triangular distribution (average them), or use a beta
distribution.
Normal Distribution: Estimate = (Optimistic + Most Likely + Pessimistic) / 3
Beta Distribution: Estimate = (Optimistic + 4 x Most Likely + Pessimistic) / 6
Back to our example. To build our log home, we would inspect each resource table from
the previous step and determine the amount of time required.
Task Duration
Name Cost
ID s
110 Excavation 6 days $5,850
120 Pour Foundation 10 days $4,700
210 Wood work 20 days $60,850
310 Electrical & Plumbing 10 days $20,260
320 Flooring 8 days $18,760
330 Finishing 12 days $16,760
410 Landscaping 14 days $7,620
TOTAL 80 days $134,800
The total of 80 days is not the final project duration because we haven’t accounted for the project
resources yet. If the resources are not available at the right time, or more resources are required
than available at a given time, the project schedule will need to be adjusted. But that’s part of the
next step
Develop Schedule
In this step we will develop the most efficient schedule for the project. This is defined as
producing the official start and end dates for each task. This can be used to direct
subcontractors as to when to schedule the work, order equipment, and to prioritize internal
resources. It also uses the critical path method to determine the shortest possible project
completion date and which tasks directly affect it. Issues that arise within those tasks can then
be dealt with on a priority basis.
Resource Levelling
In resource levelling, each task that has float is moved to its ideal place within that float in order
to “smooth” the overall use of project resources.
In the log house example above, the red highlighted boxes show days where people are working
more than 8 hours per day. It is easy to see that the Landscaping task has a very big float and
should not be completed at the same time as the Wood work. In fact, Bill and Mark can (and
should) be doing the landscaping during Electrical & Plumbing, because they are otherwise idle
(or available to another project). So we move the landscaping item to start on July 27, and then
neither Bob nor Mark will be scheduled for 10 hour days.
