Page 362 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

A S y s t e m a t i c V i e w o f G r e e n a n d M i n i m u m P r o g r a m Re q u i r e m e n t s 323

before it is constructed, not constructed before it is designed. CPMs are usually depicted
as diagrams with interconnected arrows. If the activity is listed on the arrow, then it is
referred to as an “activity on the arrow” CPM, and if the activity is depicted in a box
between arrows, then it is referred to as an “activity on the node” CPM. Time can be
included in the CPM schedule by either listing time requirements with the activity or
placing the activity on a figure similar to the bar chart where time is depicted on the
horizontal axis. The term critical path method comes from the act of adding time along
any path of arrows and determining the path which would take the longest time. The
activities along this path are considered critical since any delay in them will potentially
delay the completion of the entire project scheduled.
CPMs can be evaluated manually or with many established project scheduling
programs. Some programs are simple, and others are quite complex and include
additional opportunities to relate many features to each activity such as the workforce
needs or material needs. Adding these is usually referred to as resource loading. Other
versions add opportunities for delayed actions or only partial completion of activities
before the next starts. CPMs are frequently used and are considered to be valuable
tools in project management. Figure 8.1.1 depicts a very simplified CPM of the activities
listed in Table 8.1.3 in the activity on the node format with some delayed or early starts
and finishes on some of the activities. This is done because some of the activities within
a node may start before a predecessor is totally complete. Determination of the critical
path would need to include these delayed or early start activity estimates.
Scheduling is even more important for several reasons in sustainable construction.
First, the additional activities needed to design, collect data, and verify systems, etc.,
which are a part of the LEED process must be integrated into the design and
construction schedules. There may be cost or schedule conflicts if many of the LEED
related activities are not performed in a timely fashion. The second reason pertains to
a more detailed scheduling level. As noted in Chap. 6 on indoor environmental
quality, if construction activities are not scheduled in special ways, there are
opportunities for impacts to indoor air quality such as with mold or particulate matter.
Scheduling is one of the five principles of SMACNA for good indoor air quality. This
is the same for many other activities such as erosion and sedimentation control. If the
sediment fence is not installed on a graded site prior to a storm event, then major

FIGURE 8.1.1 Simplifi ed CPM schedule for some major construction project activities with
some overlapping starts and fi nishes. (Overall activity time in months is given.)