- Watch out
- What it costs
- Experienced readers
- Remember
- In BIMpedia
A programme looks like bars on dates. What makes it a plan is the logic: the links that say this cannot start until that has finished. Read the logic first and the bars start to mean something; skip it and you will link a 4D model to dates nobody can rely on.
Each activity has a duration. Links connect activities: most are finish-to-start (FS: B starts when A finishes); some are start-to-start (SS) or finish-to-finish (FF), sometimes with a lag (a wait, such as concrete curing). Working forwards through the links gives the earliest dates; working backwards from the finish gives the latest. The gap between the two is the activity's total float.
What float tells you
| Float | What it means | What to do |
|---|---|---|
| Zero or negative | Critical: a day lost here is a day lost at the end | Protect it, report it, plan around it |
| A few days | Some room, but it goes fast | Watch it with the critical work |
| Weeks or months | Real freedom, or a missing link | Check its successors before you believe it |
The chain of activities with no float is the critical path. It is why a three-week delay to one frame can move the handover by three weeks while a delay to a ground-floor fit-out moves nothing.
Read it in this order
- The shape: the breakdown (WBS) and the main milestones.
- The logic: pick an activity and follow what drives it and what it drives.
- The critical path: filter to critical activities and read the chain end to end.
- The checks: open ends, negative float, very long activities, leads and lags.
The coordinator sees 48 days of float on the ground-floor MEP first fix and tells the site it can wait for the late ductwork. Two weeks later the planner links the MEP to commissioning, which nobody had done; the float drops to zero and the handover moves.
The coordinator opens the programme, sees the MEP first fix has no successor, and asks the planner to link it before anyone relies on its float. With the link in, it has six days of float: the late ductwork goes to the top of the agenda.
Open the clinic's programme in the Programme Viewer and open the checks. On the ground floor, which zone's MEP first fix has no successor?
From a programme you are given:
| Activity | Float | Predecessors | Successors |
|---|---|---|---|
| Frame, level 2 | 0 days | Slab, level 2 | Roof slab; Envelope, level 2 |
| Fit-out, level 1 | 24 days | MEP first fix, level 1 | Commissioning |
| MEP first fix, level 0 | 48 days | Fit-out, level 0 (SS +6) | none |
Which activity would you protect, which would you question, and what would you ask the planner?
Key takeaways
- A programme is activities plus logic: each link says what must happen before what.
- Total float is how far an activity can slip before the finish moves; zero or less means critical.
- The critical path is the chain of activities with no float; it sets the finish date.
- Open ends (no predecessor or no successor) and long lags make float figures unreliable.