In schedules, when showing drywall installation, it is a common mistake to show it as a single item. What precedes drywall are the following: Stud framing, Installation of risers, pipes and conduits, backing or blocking, insulation material. There is an important point however. The drywall does not finish before those pipes and conduits and insulation are done installed. In other words, the predecessors have both SS and FF relationships. This would make the duration of drywall much more than actual. This excessive duration, if you are working with resources will cause inaccurate resource and % complete calculations as well.
Here is an example:
Lets say, Stud framing starts on Day 1.
At a minimum it must progress a little in order for drywall to start. So let’s say, as a predecessor to drywall, we can give a SS+ few days here
But that is usually not enough. We must also install conduits and pipes and insulation, and they must also progress enough so that we have locations that we can start drywall. So we give another SS + few days predecessors for each of these.
But then here is the problem… Drywall can not finish, before all these pipes and conduits finish. Starting drywall does not mean we can finish it as we must wait for the completion of these pipes. So what do we do, assign another predecessor with a FF relation this time? No, we can not do that. We can not assign the same activity as two different relations as predecessor. So then what is the solution?
The solution is, inserting another activity and call it “Close drywall”. This activity will have far less duration that the main drywall installation. But it will take care of that FF relation as predecessor.
Doing this will also prevent the main drywall activity to be extended excessively and “wait” for those conduits and pipes to finish. This will cause inaccuracies for total work and % complete and resource calculations.
Drywall is a very commonly used material in commercial construction projects and managing its schedule has direct effects on overall schedule. Drywall subcontractor is one of the primary subcontractors that a general contractor project manager should constantly be in touch to keep things on track.