Gantt Charts: Creating, Reading, and Interpreting Project Schedules

How architects create, read, and interpret Gantt charts (bar charts) as the primary visual tool for project scheduling, including bar construction, dependency arrows, milestone markers, baseline comparisons, and progress tracking.

ARE · Project Management

Overview

A Gantt chart is the most common way to visualize a project schedule. It displays activities as horizontal bars plotted against a timeline, showing at a glance what's happening, how long it takes, and where tasks overlap or depend on each other.

For the PjM exam, you need to create Gantt charts from project data, read them accurately, and interpret what they reveal about schedule health. That means understanding how bar length maps to duration, how dependency arrows show logical relationships, how milestones appear as diamond markers, and how the critical path stands out from activities with float.

A well-constructed Gantt chart does more than list tasks and dates. It communicates the project's logic. When you see two bars connected by an arrow, that arrow tells you the second task can't start until the first finishes (or some other logical relationship). When you see a bar shaded halfway, that tells you the activity is 50% complete. When you see a thin line behind a wider bar, that's the baseline schedule compared to current progress.

Gantt charts work for everyone on the project team. The owner can see whether milestones are on track. The project manager can spot resource conflicts where too many activities converge. Consultants can see when their deliverables fit into the total timeline. The ARE expects you to read these charts as fluently as you read floor plans.

The catch? Gantt charts show time and sequence brilliantly, but they don't show the network logic as clearly as a CPM diagram does. A Gantt chart can display dependency arrows, but when the schedule gets complex, those arrows become a tangle. That's why architects need both tools: Gantt charts for communication and tracking, network diagrams for schedule analysis.

Essential

A Gantt chart (also called a bar chart schedule) plots activities as horizontal bars on a calendar-scaled timeline. The left edge of each bar marks the activity's start date; the right edge marks the finish date; the bar length represents the duration. Activities are listed vertically, usually grouped by project phase or WBS element. ## Anatomy of a Gantt Chart A standard Gantt chart includes these elements: Activity bars. Each bar represents one schedule activity. The bar's horizontal position and length show when the activity starts, when it finishes, and how long it takes. Bars are typically color-coded or patterned to distinguish phases, disciplines, or responsibility assignments. Milestones. Milestones appear as diamonds (or similar symbols) at zero-duration points. They mark the completion of deliverables or key decision gates. On a Gantt chart, a milestone sits at a single point on the timeline rather than spanning a range. **Dependency arrows.

Professional

An architect managing a 60,000 SF elementary school project pulls up the Gantt chart three months into design development. The chart tells a story that the weekly status reports haven't captured. The structural engineering bar shows 40% progress shading, which matches the DD timeline: four weeks complete out of ten planned weeks. Good. But the mechanical engineering bar, which has a Start-to-Start relationship with a two-week lag after structural, shows only 15% progress. The structural engineer's bar is on track, but the mechanical engineer has fallen behind within the first two weeks of their effort. Looking at the dependency arrows, the architect traces the chain: structural framing feeds mechanical duct routing, which feeds electrical coordination, which feeds the reflected ceiling plan. The mechanical delay will cascade through this entire chain unless addressed now. The baseline comparison tells another story.

TLDR

A Gantt chart plots activities as horizontal bars on a calendar timeline; bar length = duration, bar position = timing
Dependency arrows connect bars to show logical relationships (FS, SS, FF); the preferred type is Finish-to-Start
Milestones appear as diamonds at zero-duration points marking key deliverables or decisions
Baseline bars (usually gray) behind current bars let you compare planned vs. actual timing at a glance
Progress shading shows percent complete; compare it to the today line to assess whether work is on track
The critical path (zero float activities) is usually highlighted in red; any slip on these bars delays the project
Gaps between bars may indicate missing logic ties; every activity should have a predecessor and successor
Overlapping bars reveal concurrent activities that may create resource conflicts
Gantt charts are best for communication and tracking; network diagrams (CPM) are better for analyzing schedule logic
Hard constraints should be used sparingly because they override the schedule logic and distort float calculations

ELI5

Think of a Gantt chart like a calendar view for a building project, except instead of appointments, you've got project tasks. Each task gets its own row, and a colored bar stretches across the calendar to show when that task starts, when it finishes, and how long it takes. Imagine planning a school play. You'd need to write the script (2 weeks), build the set (3 weeks), rehearse (4 weeks), and perform (1 night). Some of these happen one after another: you can't rehearse until the script is written. Others can overlap: you can build the set while the actors learn their lines. A Gantt chart shows all of this at once. The script-writing bar runs across weeks 1 and 2. The set-building bar starts at week 2 and runs through week 4. The rehearsal bar starts at week 3 and goes to week 6.

AREProject Management

Gantt Charts: Creating, Reading, and Interpreting Project Schedules

2 min read288 words

Reading the Schedule: What Gantt Charts Tell You

Want to track your progress and access more study tools?

Create a free account