Construction Schedule Types and Monitoring: CPM, Gantt Charts, Milestone Schedules, Float, and Critical Path Analysis

Covers the primary schedule formats used during construction, including Critical Path Method (CPM), Gantt/bar charts, and milestone schedules. Explains float calculations, critical path identification, and how architects review contractor schedules to determine construction progress under A201.

ARE · Construction & Evaluation

Overview

Construction schedules aren't just paperwork for the contractor's trailer wall. They're the primary tool you'll use as an architect to determine whether a project is on track, behind, or heading toward a dispute.

Under AIA A201, the contractor is required to submit a construction schedule for the architect's review. But the schedule format matters because each type reveals different information. A Gantt chart shows activity durations visually. A CPM network shows logical relationships between tasks and identifies which activities can't slip without delaying the entire project. A milestone schedule focuses on key completion dates without the underlying detail.

As the architect during construction observation, you need to understand all three formats well enough to evaluate the contractor's progress against the approved schedule. You also need to grasp float, which represents the amount of time an activity can slip before it affects the project completion date, and the critical path, which is the longest chain of dependent activities through the schedule.

The ARE tests your ability to read these schedules, identify when work is falling behind the critical path, and understand the impact of delays on the total project timeline. This isn't about building schedules yourself. It's about reviewing the contractor's schedule submissions and recognizing red flags during your site observations.

Essential

Three schedule formats dominate construction projects, and each one gives you a different lens on the same question: is this project on track? Gantt Charts (Bar Charts) The Gantt chart is the most common visual schedule format on construction projects. Each activity appears as a horizontal bar plotted against a time axis. The bar's length represents the activity's planned duration. At a glance, you can see which activities should be happening this week, which ones are complete, and which ones are running long. Gantt charts are excellent for communication. During site visits, a quick look at the bar chart tells you whether concrete pours, steel erection, or mechanical rough-in should be underway. The limitation? Standard Gantt charts don't show logical relationships between activities.

Professional

Consider a mid-rise mixed-use project where the general contractor submits a CPM schedule at the preconstruction meeting showing a 14-month duration. The critical path runs through the structural steel sequence: foundation completion to steel delivery to erection to metal deck to concrete topping slabs. Every activity on that chain has zero float. The mechanical and electrical rough-in activities, running in parallel, show 18 days of total float. Six weeks into construction, the architect visits the site and notices foundation work is two weeks behind the baseline schedule. The contractor's monthly update shows the critical path has shifted. The original steel delivery activity was dependent on foundation completion, so that two-week delay has already pushed the projected completion date by two weeks. The contractor hasn't submitted a time extension request yet. This situation tests several concepts simultaneously.

TLDR

Gantt charts show activity durations as horizontal bars against a timeline; great for visual communication but often lack dependency logic
CPM schedules model activities as a network with logical relationships (FS, SS, FF, SF) and identify the critical path (zero-float chain that determines project duration)
Milestone schedules track key dates (foundation complete, topped out, substantial completion) and often tie to contractual deadlines and liquidated damages
Total float = time an activity can slip without delaying project completion; free float = time it can slip without delaying any successor
Critical path activities have zero total float; any delay to them equals project delay
The architect reviews the contractor's schedule but doesn't manage or approve it in a guaranteeing sense
Monthly schedule updates compared against the baseline reveal slippage and critical path shifts
Float is typically a shared project resource, not owned by the contractor or owner alone
Near-critical activities (1 to 3 days of float) are the next potential schedule crisis
Don't confuse the construction schedule (timing) with the schedule of values (cost allocation)

ELI5

Think of building a building like planning a really complicated road trip with hundreds of stops. A Gantt chart is like a visual timeline of your trip printed on a long strip of paper. You can see that you'll be in Arizona from Tuesday to Thursday, and Colorado from Friday to Sunday. It's easy to read. But it doesn't tell you that you MUST finish Arizona before you can start Colorado (because of the route), or that you could actually do the Utah side trip whenever you want. A CPM schedule is like a detailed map that shows every route and connection. It shows you that you can't visit the Grand Canyon until you've driven through Flagstaff, and that the drive through Flagstaff takes exactly 3 hours. More importantly, it shows you the LONGEST route through all your required stops.

AREConstruction & Evaluation

Construction Schedule Types and Monitoring: CPM, Gantt Charts, Milestone Schedules, Float, and Critical Path Analysis

2 min read210 words

Why Schedule Types Matter for Construction Observation

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