Scheduling as Part of the Project Management Effort - Construction Project Scheduling and Control - page 274

an initial rough schedule. After the contractor lays out an initial rough schedule, the
contractor uses the duration to estimate the indirect cost items (overhead), such as
the following:
• Project staff (PM, project superintendent, project engineer, receptionist or sec-
retary, clerk, etc.)
• Office trailer
• Cars and trucks assigned to the project team
• Office equipment (copying machine, fax machine, computers, etc.)
• Temporary utilities (electricity, water, drinking water and ice, telephones, cell
phones, gas, portable toilets, etc.)
• Other indirect project-related expenses
The cost of most, if not all, of these items is linearly proportional to time, although
not all of them last for the entire duration of the project. This is why the estimator
needs to know the duration of the project in order to assess the indirect expenses. The
contractor also uses the time frame of the proposed project to study the impact on
other work underway or planned and the resources required.
Schedules, like cost estimates, are created on the basis of available information.
Reality (what will actually happen) is never fully known in advance. Thus, every cost
estimate or schedule includes some assumptions and guessed information (some esti-
mators like to call it a guesstimate ). A difference exists, though, between a situation
in which 90% of the information is known and 10% is assumed, and a situation in
which 20% of the information is known and 80% is assumed. Estimators use one major
criterion to differentiate, in principle, between approximate estimates and detailed
estimates. Detailed estimates are obtained by performing quantity takeoffs from the
design drawings and using the specifications. These detailed quantities are then multi-
plied by unit prices set by the estimator. Indirect expenses are added to the calculated
direct expenses to yield the grand total.
In contrast, approximate estimates are based on comparing the project under
consideration with previous similar projects (applying a unit cost, such as $140/SF)
and then making adjustments according to the size, quality, location, timing, and
so forth. No work breakdown or quantity takeoff is used in approximate estimates.
The common factor between the two methodologies is that we start with the known
information, which is supposed to be the majority for detailed estimates, and then
complement it with assumptions for the unknown. With detailed estimates, we can
look at the estimate and identify the cost of one particular item, such as a window,
paint, or even a single footing. With approximate estimates, such identification is gen-
erally not possible.
In scheduling, no such clear distinction exists between a “rough schedule” and
a “detailed schedule,” but the process is similar to that for cost estimating. We start
with the known information and complement it with assumptions. One frequent prac-
tice of designers is to show a construction activity as one bar without details. Once