PM 101 CRITICAL PATH METHOD - NIK ZAFRI

The Critical Path Method (CPM) is a project scheduling technique used to identify the sequence of activities that determine the shortest possible duration to complete a project.

The Critical Path itself refers to the longest continuous chain of dependent activities from project start to finish.

Each activity on this path has zero float/slack, meaning any delay in these activities will directly delay the entire project.

Thus : The Critical Path is the backbone of the project timeline.

1.0 WHY IS IT IMPORTANT?

a. Time Control

It tells you the minimum completion time and helps the team prioritize work. Activities on the critical path must be closely monitored.

b. Resource Allocation

It helps planners allocate labour, equipment, and materials efficiently to critical activities first avoiding idle resources or bottlenecks.

c. Progress Tracking

It allows the project manager to know exactly which delays matter most — not all delays affect the overall completion date.

d. Decision-Making

In case of unforeseen issues (e.g., weather delays, material shortages), managers can quickly decide where to fast-track or crash the schedule to recover lost time.

e. Client and Contractor Communication

The critical path schedule provides a transparent, evidence-based tool for reporting progress, negotiating time extensions, or substantiating delay claims.

2.0. MISTAKES

a. No CPM - Depending Only on Bar Chart (Gantt Chart)

Many contractors rely solely on simple Gantt charts without logic links between activities.

You can’t identify dependencies or determine which tasks truly control the project completion.

This leads to poor coordination, unrealistic timelines, and misleading progress updates.

b. Incorrect Activity Sequencing

If the logic (predecessor-successor relationship) is wrong, the identified critical path will be inaccurate.

e.g. Installing formwork is shown as independent of rebar placement, this breaks the logical flow.

c. Unrealistic Durations

Setting durations without considering actual productivity, site conditions, or resource limits will distort the path.

The CPM might show a “fake” critical path that doesn’t match real-life constraints.

d. Ignoring Resource Constraints

A CPM schedule that ignores the availability of manpower, equipment, or materials gives a misleading view of feasibility.

e. CPM not updated

Failing to regularly update progress (weekly/monthly) means the CPM becomes obsolete. The project team loses sight of the real critical path as conditions change.

f. Too Many or Too Few Activities

Over-detailed CPMs become cumbersome, while oversimplified ones miss critical logic - both make tracking difficult.

g. Not Incorporated into the Master Work Program

Sometimes CPM is prepared separately and not aligned with the master work program or baseline schedule.

This results in inconsistent reporting, claim disputes, and confusion between stakeholders.

3.0 RISKS - WITH POOR CPM OR NO CPM AT ALL

• Inability to forecast completion date accurately.
• Increased risk of cost overruns and claims.
• Miscommunication between client, consultant, and contractor.
• Ineffective monitoring - site teams don’t know what to prioritize.
• Difficulty in granting or defending Extension of Time (EOT).
• Loss of credibility with the client and project financiers.

4.0 BEST PRACTICES

• Use CPM software (e.g., Primavera P6, MS Project) with correct logic links.
• Base the durations on historical productivity rates and resource availability.
• Update CPM regularly and review float changes.
• Align CPM with the Master Work Program (MWP).
• Conduct periodic schedule reviews with all stakeholders.
• Identify opportunities for fast-tracking or crashing early if delays arise.

5.0 EXAMPLES

Let me walk through a simplified example of how the Critical Path works in a construction sequence.

Project : Building a Simple Two-Storey Structure

How CPM Helps Here

The project manager now knows that Walls & Plastering (G) is a critical activity not Roof (F) or M & E (H). If delays occur in roof work, the project can still finish on time, but wall/plaster delay will push the completion date. Hence, site resources can be prioritized for critical path tasks to prevent overall delay.

Visual CPM Network Diagram

Below is a ready-to-use sample Master Work Program (MWP) for a small building project that includes CPM calculations, plus a revised schedule showing the effect of a delay and a footnote/legend explaining delay types and how to present them in the MWP.

• Baseline activity table (with ES, EF, LS, LF, float) - CPM forward/backward pass shown implicitly in the numbers.
• Baseline Critical Path.
• Revised schedule after a 4-day delay to a critical activity (showing how completion shifts).
• Footnotes - Legend explaining delay types, columns, and how to present delays/claims in the MWP.

Baseline Master Work Program (CPM included)

Assume day counting starts at Day 0 (project start). All arithmetic is shown as totals so you can verify calculations.

a) How these numbers were obtained (summary of forward/backward pass)

Forward pass (ES → EF)

ES of a node = max(EF of all predecessors).

e.g - ES(I) = max(EF(F), EF(G), EF(H)) = max(43, 46, 44) = 46 → EF(I) = ES(I) + 5 = 51.

Backward pass (LF → LS)

LF of a node = min(LS of all successors).

e.g. LF(E) = min(LS of F, G, H) = min(39, 36, 38) = 36 → LS(E) = LF(E) − 6 = 30.

Float = LS − ES (or LF − EF)

• Baseline Project Duration = EF(J) = 53 days.
• Baseline Critical Path (zero float activities):

A → B → C → D → E → G → I → J (total 53 days)

b) Revised work program (after the 4-day delay on G)

New project duration = 57 days. Delay = 4 days (equal to the G delay) because G was critical.

c) Footnote / Legend : showing delays and how to present them in the MWP

Columns used (and how to report)

• ES / EF : Early Start / Early Finish (forward pass).
• LS / LF : Late Start / Late Finish (backward pass).
• Float : LS − ES (slack). If float = 0 → critical.

Actual Start and Actual Finish (in your live MWP, add columns) - record real progress. Compare actual vs baseline.

d) Types of Delay (legend) - short definitions and examples relevant to construction

• Excusable, Non-Compensable Delay : Delay outside contractor’s control for which time extension may be granted but no money (e.g., unusually severe weather). Mark as E-NC.

• Excusable, Compensable Delay : Delay caused by the employer/client (e.g., late variations/instructions, late approvals, late design) - contractor gets EOT and additional cost (E-C).

• Non-Excusable Delay : Contractor’s fault (e.g., poor planning, labour shortage due to contractor’s hiring failure) : contractor liable for EOT denial and possible liquidated damages (NE).

• Concurrent Delay : Two or more delays happening at the same time where at least one is employer’s and one contractor’s; entitlement is complex and often needs separate forensic analysis (CONC).

• Acceleration/Owner-Directed Acceleration - Owner asks contractor to compress schedule; if owner-directed, costs may be compensable (ACC).

e) How to show delays in the MWP (recommended columns and notes)

• Baseline ES/EF : original planned.
• Current Forecast ES/EF : recalculated every update cycle (weekly/bi-weekly).
• Actual Start/Actual Finish : daily/weekly progress entries.
• Variance (days) - Current Forecast EF(J) − Baseline EF(J). (Shows total delay)

f) Delay Type : use legend codes (E-NC, E-C, NE, CONC).

i) Supporting Docs : RFI no., delivery note, weather log, employer instruction no., photos, site daily logs. Always attach proof for claims.

ii) Color / formatting convention (suggested):

• Red row = activity on the current critical path.
• Yellow cell = activity experiencing a delay.

Column for “Claim / EOT requested” with date and amount (if applicable).

g) Practical tips for your MWP + CPM on construction projects

• Baseline and Updates: Keep a clear baseline schedule (approved) and publish regular updates (weekly/fortnightly). Each update must include actual start/finish, and a recalculated CPM (forward/backward pass).

• Resource-aware CPM: CPM assumes unlimited resources; if your site is resource-constrained, overlay a resource-levelling run or show resource conflicts separately.

• Maintain Audit Trail: For every delay mark, attach contemporaneous evidence: delivery tickets, RFIs, site weather logs, photos, signatures. This is essential for EOT or claims.
  
  
• Identify Recovery Options Early: If a critical activity is delayed, evaluate crashing (add labour/equipment) or fast-tracking where technically safe - capture cost vs time trade-off.

• Watch for Hidden Critical Paths: Frequent logic checks - wrong links create wrong critical path. Keep activities at an appropriate level of detail (not too coarse, not too granular).

• Be explicit about calendars: Use the same work calendar (public holidays, weekends) when computing durations and ES/LS dates.

6.0 CONCLUSION

In construction, time is not just money, it’s control, credibility, and coordination. The Critical Path Method (CPM) remains the backbone of effective project scheduling because it identifies where time truly matters. Through a well-prepared CPM-based Master Work Program, project teams can visualize the entire construction process, anticipate bottlenecks, and make informed decisions when challenges arise.

Conversely, projects without a proper CPM analysis often fall prey to confusion, miscommunication, and costly delays. Without understanding which activities drive the completion date, both contractors and clients risk losing grip over schedule integrity, resource planning, and even contractual entitlements such as Extension of Time (EOT).

Ultimately, mastering the CPM is not just about software proficiency - it’s about discipline, foresight, and accountability. It empowers project stakeholders to act on facts rather than assumptions, ensuring that every day on site contributes toward successful, timely delivery.