5.1 Project Planning, WBS, Logic & Resources

5.1 Project Planning, WBS, Logic & Resources

Effective project planning and scheduling are vital responsibilities of a licensed commercial general contractor. Construction schedules are operational roadmaps for coordinating trades, procurement, and equipment. When the contract incorporates an accepted baseline and update procedure, those records can also become important evidence for progress, delay, and time-extension analysis. The industry standard for planning and managing complex commercial construction is the Critical Path Method (CPM) network analysis.

---

Work Breakdown Structure (WBS) & Activity Definition

Before developing a CPM schedule, the project scope must be systematically decomposed using a Work Breakdown Structure (WBS). A WBS is a deliverable-oriented hierarchical decomposition of the total scope of work to be executed by the project team.

                      ┌─────────────────────────────────────────┐
                      │          TOTAL PROJECT SCOPE            │
                      │      (Commercial Office Building)       │
                      └────────────────────┬────────────────────┘
                                           │
         ┌─────────────────────────────────┼─────────────────────────────────┐
         ▼                                 ▼                                 ▼
┌─────────────────┐               ┌─────────────────┐               ┌─────────────────┐
│  Substructure   │               │   Superstructure│               │  MEP Rough-In   │
└────────┬────────┘               └────────┬────────┘               └────────┬────────┘
         │                                 │                                 │
 ┌───────┴───────┐                 ┌───────┴───────┐                 ┌───────┴───────┐
 ▼               ▼                 ▼               ▼                 ▼               ▼
┌─────────┐     ┌─────────┐       ┌─────────┐     ┌─────────┐       ┌─────────┐     ┌─────────┐
│Excavation│    │Footings │       │Cast Columns│  │Deck Slab│       │HVAC Duct│     │Plumbing │
└─────────┘     └─────────┘       └─────────┘     └─────────┘       └─────────┘     └─────────┘

Hierarchical Levels of a WBS

1. Project Level: The overarching facility or contract deliverable.
2. Subproject / Phase Level: Major project milestones or physical zones (e.g., Substructure, Core & Shell, Interior Fit-Out, Site Civil).
3. Deliverable / System Level: Discrete structural, architectural, or MEP systems (e.g., Foundation Footings, Structural Steel Erection, Exterior Curtain Wall).
4. Work Package Level: The lowest level of the WBS that can be assigned to a specific trade contractor, budgeted, monitored, and controlled.
5. Activity / Task Level: The individual work components derived from work packages that have measurable durations, required resources, specific start and end criteria, and logical relationships to other activities.

Activity Duration Estimating

Activity durations must reflect realistic field productivity rates, labor crew sizes, equipment capacity, and site constraints. Common estimation techniques include:

• Parametric Estimating: Calculating duration based on historical unit productivity (e.g., $150\text{ LF of drywall partition per day for a 4-person crew} \times \text{Total LF} = \text{Days}$).
• Three-Point Estimating (PERT): Incorporating uncertainty using optimistic ($O$), most likely ($M$), and pessimistic ($P$) durations: $\text{Expected Duration } (T_e) = \frac{O + 4M + P}{6}$

---

Precedence Diagramming & Activity Dependencies

In precedence diagramming (Activity-on-Node / AON networks), activities are represented by nodes connected by dependency lines that dictate sequence based on physical constraints, safety protocols, and resource logic.

Lead Time vs. Lag Time

• Lag Time (+): An inserted waiting period between activities where no active work occurs. A standard example is concrete curing: Activity A (Pour Foundation) to Activity B (Strip Formwork & Backfill) has a finish-to-start relationship with a 7-day curing lag ($FS + 7\text{ days}$).
• Lead Time (-): An acceleration parameter that allows a successor activity to begin before its predecessor is completely finished (negative lag). For example, Drywall Hanging can start 3 days before Framing finishes ($FS - 3\text{ days}$).

---

Logic quality and resource reality

A valid network distinguishes physical logic from preferential logic and resource constraints. Waterproofing cannot precede the substrate it covers; that is physical. Choosing to complete every room on one floor before starting the next may be a crew strategy that can change. A crane shared by steel and precast can create a resource conflict even if the CPM network shows both activities available. Document the reason for constraints so later updates do not preserve obsolete logic.

Avoid open ends, excessive lags, and date constraints that hide the driving path. Model curing, review, fabrication, delivery, inspection, and turnover as visible activities when they can control work. Break an activity when different floors or zones can progress independently. Then resource-load or at least reconcile labor, equipment, long-lead procurement, access, and cash needs.

At each update, record actual starts and finishes, remaining durations, changed logic, new activities, and the data date. Do not overwrite the accepted baseline. A recovery schedule is a forward plan—often using added crews, resequencing, or changed means—not permission to falsify past status. The exam distinction is simple: CPM calculates time from logic and duration; resource leveling can delay otherwise available work and may change the critical path.