How to build a construction schedule and find the critical path

What is a construction schedule, and why pair it with the critical path?

A construction schedule (iş programı in Turkish) shows which activities make up the job, how long each takes, in what order and with which resources. The Gantt chart is its best-known view, but the logic links between activities are the actual plan. The Critical Path Method (CPM) uses those links to compute the shortest possible duration and the activities that drive it. Delay one of them and the project is late; delay anything else and you have float to absorb it. On site, that tells you where scarce crews, cranes and concrete pumps go first.

How do you build a schedule step by step?

1. Work breakdown structure. Split the job by block, floor and trade, down to work one crew can finish in one place.
2. Activities. Measurable items, at least 1 day and no longer than your reporting period, usually one month.
3. Durations. Quantity ÷ (crews × daily output), in working days, with holidays and weather downtime in the calendar.
4. Logic. Predecessor and link type for every activity; only the start has no predecessor and only the finish has no successor.
5. Resources. Assign crews, plant and long-lead materials, and resolve clashes.

Lag is waiting time on a link, such as the stripping time after a pour, which the structural engineer sets.

How is the critical path calculated? A worked example

The forward pass gives each activity its early start (ES = the largest early finish of its predecessors) and early finish (EF = ES + duration). The backward pass from the project finish gives late finish (LF = the smallest late start of its successors) and late start (LS = LF − duration). Total float is LS − ES. Free float is the smallest ES of the successors minus the activity's own EF. All links below are FS with no lag; days count from 0.

The project takes 36 working days and the critical path is A → B → C → D → F → G → J (6 + 2 + 3 + 6 + 1 + 10 + 8 = 36). Earthing can slip 7 days without moving the pour. Wall waterproofing has 1 day of total float but no free float: a 1-day slip leaves the finish alone but eats the backfill's float.

How do you read a Gantt chart and track delay?

Look for the critical bars (usually red), the logic arrows, the float and the today line. Any critical bar left unfinished to the left of the today line has already moved the finish. If moving one bar does not move its successors, there is no CPM behind the chart. Freeze a baseline when the programme is approved, update actual starts, percent complete and remaining durations weekly, recalculate, and record the cause of every delay; that record supports extension of time claims. Link design-driven delays to your revision log.

What are the rules on Turkish public works?

On public works contracts, article 17 of the General Specification for Construction Works (Yapım İşleri Genel Şartnamesi) applies. The contractor submits the programme within 15 days of site handover; if the employer rejects it, there is one penalty-free 5-day correction window; after that, each day late costs 10% of the contract's daily delay penalty. A revised programme is due within 7 days of notice after a time extension, scope change or budget change. The programme must also show monthly quantities and how each year's budget allocation (ödenek) is spread over the months, and where the contract pays for materials on site (ihzarat), nothing is paid for work or materials until the programme is approved. Private contracts follow whatever the contract says.

What goes wrong when importing from MS Project or Primavera?

• Calendars that do not carry over, so dates shift.
• Date constraints that override the logic and fake a critical path.
• Links on summary tasks that other software reads differently.
• Mixed hour, day and week units causing rounding.
• Lost activity IDs that break links to payment and daily reports.

Checklist

• Every activity has a predecessor and a successor, except start and finish.
• Durations come from quantities and are in working days.
• The critical path is driven by logic, not constraints.
• Long-lead procurement and approvals are activities.
• A baseline is frozen and there is a weekly update day.

How does this work in Santix?

In Santix you enter tasks, milestones and FS, SS, FF and SF links with lag; Santix calculates the critical path and total and free float. The iPad shows a landscape Gantt chart, the phone a list, with filters for critical and late work. Room-level progress marked on the drawing rolls up to the linked task. You can import MS Project XML and Primavera P6 XER files. See schedule and Gantt and pricing. The app interface is in Turkish.

Sources

• General Specification for Construction Works (consolidated copy), arts. 4 and 17
• Ministry of Environment, Urbanisation and Climate Change, High Technical Board opinion 2022/232

Checked on 13 November 2026. The CPM example was verified by hand and by script.