Tight scheduling demands that the trades complete their work on
time. They must stay on schedule or face the wrath of their builder. Many builders have
successfully used this method to cut weeks off of their build schedule.
The dark side of this scenario is that the trades add extra safety
to complete their work. It doesn't take long for the trades to learn that the more safety
time they can add, the more likely they are to beat the schedule. Even if they can beat
the schedule, they will take the allotted time for fear that the extra time may be taken
away.
A framer that averages five days will want a seven-day schedule
because occasionally it takes that long. The foundation contractor adds two days for
contingencies. Plumbing, electrical, and HVAC each add a day for possible problems. Before
you know it, the single largest activity that appears scattered throughout the overall
plan is safety time set aside for occasional delays. In our example, seven days of safety
time were used to set a firm date for the pre-drywall inspection. The resulting cost is
enormous. Using safety time more efficiently is an excellent opportunity for reducing
overall build time.
Manufacturing industries have been reducing their cycle time by
changing their scheduling methods. They recognize that scheduling a single group of as few
as four combined activities has higher schedule reliability with half the total safety
time.
EG&G Pressure Science, a Maryland aerospace parts manufacturer,
used a computerized scheduling system to tightly schedule and control step by step
production activities. After an initial reduction, cycle times stabilized at new levels.
Wishing to reduce cycle time further they established cell teams, groups of craftsmen that
work together, for each major phase of production. The cell teams manage their own
internal production schedule. Now the computerized scheduling system controls only
production between cells. Overall production cycle time was cut in half while scheduling
was simplified by a factor of four.
Adapting this approach to builders, cell teams consisting of
multiple trades can be organized for each phase of construction. Each trade in the cell is
scheduled using the normal task time, without safety time. A single safety time is then
scheduled at the end of the phase.
On at least half the jobs, each trade can be expected to meet or
beat their scheduled duration. On the other jobs, the trades would need to be flexible
enough to slide back when one of the previous trades experiences a delay. The scheduled
completion time for the phase would stay on time because delays can be absorbed by the
phase safety time.
Builders have been following manufacturing’s lead in the
evolution of scheduling methods. Whether builders will continue to follow the same
evolutionary path or jump ahead remains to be seen. Let's keep an eye on this one.