Gantt, Network Diagram, or Line of Balance?

A Gantt chart, a network diagram, and a line of balance chart can all show the same project. They answer different questions. The Gantt shows when. The network diagram shows why. The line of balance shows how fast, and whether crews will run into each other. This post explains what each view is good for, what each hides, works a small line of balance example for a multi-story building, and ends with a short guide to picking the right one for the job in front of you.

Gantt charts

A Gantt chart is a list of activities with a horizontal bar for each, laid against a timeline. It's the view almost everyone recognizes, and it's the default in P6, MS Project, and nearly every scheduling tool.

What it does well:

• Shows dates at a glance. When does steel start? When does the roof get done? You can answer by looking.
• Groups well. Sort by WBS, area, trade, or responsibility and the bars still make sense. See Activity Codes, Filters, and Layouts That People Use.
• Prints and shares. A one-page Gantt of the next three months is the most useful handout at a subcontractor meeting.
• Shows progress against a baseline. A baseline bar under each current bar makes slippage obvious.

What it hides:

• Logic. A Gantt can show relationship lines, but on a schedule with hundreds of activities they become a tangle, so most people turn them off. Then you can't tell whether a gap between two bars is float, a lag, or a missing tie.
• Why something is critical. Red bars tell you what's critical, not what's driving it.
• Production rates. Ten floors of drywall show up as ten bars. Whether the drywall crew is going to catch the framers isn't visible unless you do the math yourself.

An important distinction: a Gantt chart drawn from a CPM schedule is a view of a network. A Gantt chart drawn in Excel with bars typed in by hand is just a picture of dates. They look the same and behave nothing alike. When one bar moves in the CPM version, its successors move. In the hand-drawn version, nothing else does. See Excel Schedules: When They're Fine and When They're Not.

Modern tools blur the line between view and editor. In schedule.construction, for example, the Gantt is interactive: you drag or resize bars and draw dependencies directly on the chart, and the CPM recalculates. That's convenient, but the underlying point stands. The bars are output. The logic is the schedule.

Network diagrams

A network diagram shows activities as boxes (nodes) connected by arrows for each relationship. Most modern CPM uses the precedence diagramming method (PDM), also called activity-on-node, where boxes are activities and arrows are relationships, including SS, FF, and SF types. The older arrow diagramming method, activity-on-arrow, drew activities as arrows between event nodes and could only show finish-to-start logic without dummy activities. You'll still see it in textbooks; you won't see it much in practice.

What it does well:

• Shows logic explicitly. Every relationship is visible. You can trace a path from TCO back to notice to proceed and see every tie along the way.
• Reveals bad logic. Open ends, redundant ties, and loops stand out in a network view far more than in a Gantt. See Open Ends and Dangling Logic.
• Fits analysis work. A fragnet for a change order, or the logic behind a time impact analysis, is easiest to explain as a small network diagram. See Fragnets: What They Are and How to Write One.
• Teaches CPM. It's the natural way to show the forward and backward pass. See Forward and Backward Pass, Worked by Hand.

What it hides:

• Time. A standard network diagram isn't drawn to scale. A 2-day inspection and a 60-day fabrication take the same size box.
• Readability at scale. A full network diagram of a 1,500-activity schedule is a wall of boxes. It's useful for focused review of a path or a fragnet, not as a whole-project view.

A middle ground is the time-scaled logic diagram: bars on a timeline, like a Gantt, but arranged and connected so the logic reads clearly. It's good for showing a specific path or a recovery plan to people who don't read schedules every day.

Line of balance

Line of balance (LOB), also called a flowline or, on horizontal jobs, a linear schedule or time-distance diagram, plots location on the vertical axis and time on the horizontal axis. Each trade's work is a sloped line moving through locations: floor 1 to floor 12, unit 1 to unit 200, station 0+00 to station 150+00.

The slope is the production rate. A steep line is fast; a shallow one is slow. Where two lines converge, a following trade is catching up to the one in front of it. Where they cross, the schedule is asking two crews to be in the same place at once.

A worked example: framing and drywall on a 12-story building

Interior framing takes 4 working days per floor. Drywall takes 3 working days per floor. Drywall can start a floor when framing on that floor is done. Days are counted 0-based: framing floor 1 starts at day 0.

Framing:

Floor n framing: start 4(n - 1), finish 4n
Floor 1: 0 to 4    Floor 2: 4 to 8    ...    Floor 12: 44 to 48

If drywall starts floor 1 as soon as it can, on day 4, and runs at its own pace:

Floor n drywall start = 4 + 3(n - 1)
Floor 2: start 7, but framing on floor 2 finishes day 8

Drywall catches framing on the second floor. The drywall line is steeper than the framing line, so they converge immediately. In the field this looks like a drywall crew standing around every few days waiting for the framers. Either drywall stops and starts, or it starts later.

To run drywall continuously, work backward from the top floor. Drywall on floor 12 can't start before framing finishes it on day 48:

Drywall start on floor 1 = S
Drywall start on floor 12 = S + 3 x 11 = S + 33
Need S + 33 >= 48, so S >= 15

Start drywall on floor 1 at day 15 instead of day 4. It then runs floor to floor without interruption and finishes floor 12 on day 51. Starting earlier doesn't finish any sooner; it just adds idle time and remobilization. A CPM schedule with per-floor FS ties would start drywall on floor 1 at day 4 and quietly insert a one-day gap before every floor after it. Nothing flags the idle crew. The LOB view shows why that's a bad plan.

This is the core value of LOB: it shows production rates and crew continuity, which CPM doesn't model directly. On repetitive work (high-rise residential, hotels, dormitories, multifamily, parking structures, and linear jobs like pipelines, roads, and rail), that's often the question that matters most.

What LOB hides:

• Non-repetitive work. Site work, the lobby, the mechanical penthouse, and commissioning don't fit on a location axis.
• Detailed logic. It shows that trades follow each other, not the specific ties between them.
• Tool support. P6 and MS Project don't draw LOB charts natively. It's often done in a spreadsheet or a dedicated location-based or linear scheduling tool alongside the CPM schedule.

Picking the right view

In practice most jobs use more than one. The CPM network is the source of truth for logic and dates. The Gantt is how most people read it. On repetitive work, a line of balance alongside the CPM schedule catches crew-flow problems the CPM math won't flag.

Key takeaways

• Gantt charts show when. Network diagrams show why. Line of balance shows how fast.
• A Gantt from a CPM schedule is a view of logic. A hand-drawn Gantt is just dates.
• Use network diagrams for logic review, fragnets, and delay analysis.
• Use line of balance on repetitive work to check production rates and crew continuity.
• A CPM schedule can be mathematically correct and still have crews stacking up. LOB shows it.