In This Article
Why Scheduling Matters
In construction, time is money — literally. General condition costs (superintendents, trailers, cranes, site security) accrue daily regardless of production progress. Delayed occupancy means delayed revenue for the owner. Delayed milestones trigger contractual penalties. And when delays occur and blame is disputed, a rigorous schedule becomes the primary evidence in a delay claim — worth far more than after-the-fact recollection.
For structural scope specifically — which typically drives the longest lead activities — schedule control is critical. Structural steel lead time from order to delivery is often 16–24 weeks. Drilled shafts cannot begin until the geotechnical report is approved. Concrete pour sequences must be coordinated with crane availability. Getting these activities wrong pushes everything downstream.
Work Breakdown Structure
Every schedule begins with a work breakdown structure (WBS) — a hierarchical decomposition of all project work into manageable packages. For a structural renovation, a typical WBS might be:
- Level 1: Project
- Level 2: Phase (Design, Permitting, Construction, Closeout)
- Level 3: Construction Scope (Demolition, Foundation, Structural Frame, Facade, MEP, Finishes)
- Level 4: Work Package (Foundation Excavation, Foundation Forming, Foundation Concrete, etc.)
Each work package becomes an activity in the schedule. Activities must have clear, measurable start and finish criteria — "concrete placement complete" is measurable; "work ongoing" is not.
CPM Schedule Basics
The Critical Path Method (CPM) was developed in the 1950s jointly by DuPont and RAND Corporation for industrial project scheduling. CPM represents project work as a network of activities linked by logical relationships:
- Finish-to-Start (FS): Activity B cannot start until Activity A is complete (most common)
- Start-to-Start (SS): Activity B cannot start until Activity A has started (allows overlapping work)
- Finish-to-Finish (FF): Activity B cannot finish until Activity A has finished
- Start-to-Finish (SF): Rarely used; B cannot finish until A starts
Each activity has a duration (the estimated time required, in working days), an early start and early finish (forward pass computation), and a late start and late finish (backward pass computation). The forward and backward pass together yield the critical path and all float values.
Critical Path & Float
The critical path is the longest continuous chain of activities through the project network. It equals the project duration. Activities on the critical path have zero total float — any slip in a critical activity directly slips the project completion by the same amount.
Float (also called "slack") is the schedule flexibility in non-critical activities. It exists because not all activities need to occur exactly in sequence — some can be performed concurrently, and some can start later without affecting the project completion.
Total Float vs. Free Float
Total Float (TF) = Late Start – Early Start = Late Finish – Early Finish. An activity's total float is the time it can be delayed without delaying the project end date. Total float is shared among all activities on a logic chain — using up TF on one activity reduces TF for all subsequent activities in the chain.
Free Float (FF) = Early Start of next activity – Early Finish of current activity. Free float is the time an activity can be delayed without affecting the earliest possible start of any immediately following activity. Unlike total float, free float is private to the activity — using it doesn't affect downstream activities.
Schedule Compression: Crashing & Fast-Tracking
When the network-calculated project duration exceeds the required completion date, schedule compression is required. Two principal methods:
Fast-Tracking
Fast-tracking overlaps activities that would normally be sequential. Design and construction can overlap; structural work can begin before all architecture drawings are complete; mechanical work can begin in completed structural bays while framing continues in others. Fast-tracking increases risk of rework if later design changes affect earlier constructed work, but may be the only option when schedule recovery is required.
Crashing
Crashing adds resources to critical path activities to reduce their duration — additional crews, overtime shifts, multiple-crane operations, or split work fronts. Crashing has a direct cost premium. Crash cost analysis calculates the marginal daily schedule acceleration cost foreach activity, and applies resources to the cheapest-to-crash critical activities first until the target completion is achieved.
Delay Analysis Methods
When actual progress deviates from the planned schedule and a delay claim arises, delay analysis reconstructs what happened and who caused it. Common methods:
| Method | Description | Best Used When |
|---|---|---|
| As-Planned vs. As-Built | Compares original planned schedule to actual progress; gap = delay | Simple projects; contemporaneous records exist |
| Impacted As-Planned (TIA) | Adds delay events to as-planned schedule to show impact | Prospective time extension requests during construction |
| Collapsed As-Built | Removes delay events from as-built schedule to show "but for" duration | Retrospective analysis; when as-planned is not well-defined |
| Windows Analysis | Divides project into time windows; analyzes delays event by event | Complex concurrent delay situations; litigation |
Scheduling Software
Oracle Primavera P6 is the industry standard for large and complex construction projects. P6 handles resource-loaded schedules, multiple project portfolios, earned value management, and produces industry-standard schedule outputs. It is typically required by owners and general contractors on major public and private projects in NYC.
Microsoft Project is more accessible for smaller projects and teams without P6 expertise. It produces CPM output but lacks the resource and portfolio management depth of P6. For most mid-size renovation and structural projects, MS Project provides adequate schedule management capability.
Frequently Asked Questions
The critical path is the longest sequence of dependent activities from start to finish. Any delay to a critical path activity directly delays project completion by the same duration. Critical path activities have zero total float.
Total float: how much an activity can slip without delaying project completion (shared among the logic chain). Free float: how much an activity can slip without delaying the earliest start of immediately following activities (private to the activity).
A forensic reconstruction of a project schedule to determine whether delays occurred, how long they were, and which party caused them. Methods include As-Planned vs. As-Built, Windows Analysis, and Collapsed As-Built. Contemporaneous records are essential for a defensible analysis.
Primavera P6 for large complex projects (required by most major owners and GCs). Microsoft Project for mid-size projects. Both produce CPM outputs. For delay analysis and litigation, P6 is preferred.
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