7.2 Work Breakdown Structures, Scheduling Methods & Dependency Logic

Work Breakdown Structure (WBS)

A Work Breakdown Structure (WBS) is a hierarchical decomposition of the total scope of work to be carried out by the project team. It breaks down complex, multi-year projects into small, distinct, and manageable units:

• Level 1: Project Level (e.g., Civic Health Center)
• Level 2: Phase Level (e.g., Phase 03 - Construction Documents)
• Level 3: Work Package Level (e.g., Architectural Building Enclosure Package)
• Level 4: Task Level (e.g., Exterior Wall Details, Window Head/Jamb/Sill Detailing)
• Level 5: Sub-task / Assignment Level (e.g., Draft Sheet A-501 Detail 4 - Masonry Parapet Flashing)

The 100% Rule

The cardinal rule of the WBS is the 100% Rule: the Work Breakdown Structure must include 100% of the scope defined by the project contract and encompass all deliverables—internal, external, and interim. The sum of the work at child levels must strictly equal 100% of the work represented by the parent node, with zero omissions and zero scope creep additions.

Work Packages as Management Units

A Work Package is the lowest level in a WBS hierarchy that can be independently budgeted, scheduled, assigned to a specific individual or discipline, and monitored for earned value. In architectural practice, a work package typically correlates to a specific drawing sheet, a specification division, or an engineering coordination package.

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Project Scheduling Methodologies

Architectural project managers rely on three scheduling techniques, and each answers a different question. A milestone chart lists key dates — schematic design sign-off, permit application, substantial completion — and gives principals and clients an executive summary with no task-level detail. A Gantt (bar) chart, developed by Henry Gantt, plots activities along a calendar timescale and shows durations and overlaps clearly, but standard bar charts disguise the logical dependencies between tasks. The Critical Path Method (CPM) models activities as a network linked by explicit relationships and calculates the longest path through the project, producing the earliest and latest that each activity can start and finish without extending the completion date.

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Scheduling Methods Compared

Three scheduling techniques appear on the exam, and each answers a different question.

CPM is the method the ARE tests quantitatively, because it is the only one that produces float and therefore a defensible answer to "can we absorb this delay?"

Dependency Relationships

CPM logic is built from four relationships, though finish-to-start dominates design schedules:

• Finish-to-Start (FS): B cannot start until A finishes. Code analysis finishes before the egress plan starts.
• Start-to-Start (SS): B cannot start until A starts. Specification writing starts once drawing production starts.
• Finish-to-Finish (FF): B cannot finish until A finishes. The door schedule cannot finish until the floor plans finish.
• Start-to-Finish (SF): rare in design work.

Lead and Lag

A lag delays a successor after its predecessor — a two-week jurisdictional review sitting between submission and comment resolution. A lead (negative lag) lets a successor begin before its predecessor completes. Both change the critical path, and both are a frequent source of schedule items where the arithmetic looks wrong until the lag is accounted for.

Exam Tip: The 100% Rule and the critical path answer different questions. The WBS guarantees nothing in scope is missing. The CPM network guarantees you know which missing thing delays the project. A complete WBS with no schedule logic tells you what to do but not what to do first.

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Estimating Activity Durations

A schedule is only as good as the durations inside it, and three estimating techniques appear in practice:

• Analogous estimating applies the actual duration of a comparable past project or phase to the current one. It is fast and appropriate early, when the design is still undefined, but it inherits whatever was unusual about the comparison project.
• Parametric estimating multiplies a measured unit rate by the quantity of work — hours per sheet, hours per specification section, hours per thousand square feet. It is the most defensible method for production tasks in construction documents.
• Three-point estimating combines an optimistic duration (O), a most likely duration (M), and a pessimistic duration (P). The PERT weighted mean is (O + 4M + P) ÷ 6, which pulls the estimate toward the most likely value while still carrying the tails.

Work out a case: a consultant coordination task estimated optimistically at 8 days, most likely at 12 days, and pessimistically at 28 days gives (8 + 48 + 28) ÷ 6 = 14 days — not the 12 days a manager would have written down by instinct. The long pessimistic tail moves the answer, and recognizing that is the point of the technique.

Resource Loading and Leveling

Assigning durations without assigning people produces a schedule nobody can staff. Resource loading attaches hours and a named person or discipline to each activity. Resource leveling then shifts start dates so that no individual is committed beyond their available hours. Leveling consumes float and can push out the completion date, which is why it belongs before the schedule is issued to the client rather than after the client has accepted a date the office cannot staff.

Baselining and Updating the Schedule

Once the client accepts the schedule it becomes the baseline — the fixed reference against which all later performance is measured.

• Progress updates record actual start and finish dates and remaining durations at a fixed interval, typically monthly in design.
• Variance is measured against the baseline, never against last month's revised schedule. Quietly re-baselining to absorb slippage destroys the only record that shows where the delay came from and who caused it.
• A revised baseline is appropriate only when scope changes, and it should be issued formally alongside the change instrument that caused it.

Rolling wave planning handles the reality that distant work cannot be detailed early: near-term activities are scheduled at work-package granularity while later phases stay at phase granularity, and detail is added as each phase approaches.