P6 Activity Types Explained
Last reviewed 16 September 20268 min read
Task Dependent, Resource Dependent, LOE, WBS Summary and milestones — which one, and what each does to your dates
🟩 In one line: Task Dependent is the default for every piece of production work; milestones mark contractual and interface dates; LOE carries scaffold, hoists and supervision; Resource Dependent and WBS Summary are used rarely and deliberately — and the wrong type quietly changes which calendar drives the activity and whether it can hold logic at all.
👤 Who this is for: J/M. Prerequisites: setting-up-a-p6-project, calendar-setup-and-holidays. Companion to p6-duration-types-explained and percent-complete-types.
First, let's be honest about why this page exists
Activity type is set on the General tab and almost nobody looks at it after the project is created. Then a 7-day curing activity finishes two days late because it was Resource Dependent and inherited a 6-day labour calendar, or a tower crane shows as critical with 30 days of float because someone made it a Task rather than an LOE, or a WBS Summary activity refuses to take the relationship the reviewer asked for.
Six types, one table, and the rules for when each is used. That is all this page is.
🟨 The standard — what "good" looks like
| Source | What it asks for (paraphrased) | Type it affects |
|---|---|---|
| DCMA 14-Point, all metrics | Exclude LOE and summary activities from the tests | LOE and WBS Summary must be correctly typed so the exclusion works |
| DCMA Metric 8 (High Duration) | Incomplete tasks > 44 working days flagged | Scaffold and supervision typed as Task will fail; as LOE they are excluded |
| GAO Schedule Assessment Guide, BP 1 and 2 | Capture all activities; sequence with logic | Milestones for contractual dates; every Task with logic |
| PMI Practice Standard for Scheduling, 2nd ed. | Activity types and their behaviour understood and applied consistently | All |
| AACE RP 38R-06 | Basis records activity type conventions | The rules below go in the SBM |
| Client schedule specifications (typical Gulf) | Often limit LOE to a percentage of activities and forbid WBS Summary | Check the spec; the conventions here are compatible with most |
🟢 Rule: production work is Task Dependent; contract and interface dates are milestones; time-spanning support (scaffold, hoist, crane, supervision, preliminaries) is LOE; Resource Dependent only where a resource's own calendar must drive the work; WBS Summary almost never.
How it actually works
1. The six types, side by side
| Type | Duration comes from | Calendar used for scheduling | Can hold relationships | Can hold constraints | Counts in DCMA tests | Typical use |
|---|---|---|---|---|---|---|
| Task Dependent | Typed by the planner (or from resources per duration type) | Activity's own calendar | Yes | Yes | Yes | All production work — pour, block, first fix, testing |
| Resource Dependent | Typed | Each assigned resource's own calendar | Yes | Yes | Yes | Work whose timing is governed by a resource that has a different calendar from the activity — shared crane on a 24 h calendar, specialist crew on a 5-day calendar |
| Level of Effort | Calculated from its predecessors' and successors' dates | Activity's calendar for display; dates from linked activities | Yes (predecessors and successors drive its span) | No | No — excluded | Scaffold, hoist, tower crane, site supervision, preliminaries, subcontractor management |
| Start Milestone | Zero | Activity's calendar | Yes | Yes | Yes (as an event) | Commencement, access granted, IFC issued, notice to proceed |
| Finish Milestone | Zero | Activity's calendar | Yes | Yes | Yes | Contractual completion, key dates, sectional completions, handovers |
| WBS Summary | Calculated from all activities in its WBS node | Activity's calendar for display | No | No | No — excluded | Rarely; a visible bar for a WBS node when the layout can't show WBS bands |
2. Rules per type
Task Dependent
- Default for the project (Project Details → Defaults).
- Calendar assigned explicitly: site 6-day for labour work, 7-day for curing, 24 h for shutdown work.
- With Fixed Duration & Units, adding or removing resources doesn't change the duration — the planner controls it.
Resource Dependent
- Use only when the resource calendar is the point: a tower crane on a 24-hour, 7-day resource calendar lifting for activities on a 6-day site calendar; a client-supplied inspector working 5 days.
- Danger: the activity ignores its own calendar. A curing activity made Resource Dependent with a labour resource will cure on the labour calendar. Curing is a Task on a 7-day calendar — never Resource Dependent.
- Every Resource Dependent activity gets a Notebook line saying which resource calendar drives it.
Level of Effort
- Predecessor = the first activity it supports (SS); successor = the last (FF). Its duration is whatever the span between them is after each reschedule.
- No constraints allowed; no float of its own; excluded from DCMA, BEI, CPLI.
- Convention: scaffold, hoist, crane, supervision, preliminaries, subcontractor management = LOE, never Task. A Task version of "Tower crane" with a typed 400-day duration fails DCMA Metric 8 and confuses every float report.
- Keep LOE to ≤ 5–10% of activity count and ≤ 5–10% of baseline hours where cost-loaded (progress-measurement-and-rules-of-credit).
- Resources on an LOE spread across its span — right for supervision hours, wrong for anything measured.
Milestones
- Zero duration; Start Milestones for things that begin (access, IFC, commencement), Finish Milestones for things that end (completion, handover).
- Contractual milestones carry a Finish On or Before constraint with the contract reference; planning milestones carry none.
- Planned completion and contractual completion are two separate Finish Milestones (float-ownership-and-contract).
- Milestones can take resources in P6 but shouldn't — nothing is earned on a date.
WBS Summary
- Cannot have predecessors or successors — which is the reason to avoid it. Reviewers asking for logic on a summary activity are asking for something P6 does not allow.
- Use WBS bands in the layout instead. If a summary bar is genuinely needed for a client layout, one WBS Summary per major node, clearly named, excluded from all metrics.
- Many Gulf specs prohibit it outright.
3. Checking a schedule for type errors — 3 minutes
| Filter | Finds | Fix |
|---|---|---|
| Type = Task, Original Duration > 44 days, name contains scaffold / hoist / crane / supervis / prelim | Support work typed as production | Change to LOE; relink SS to first supported, FF to last |
| Type = LOE, count ÷ total activities > 10% | LOE overuse | Convert genuine work back to Task |
| Type = Resource Dependent | Every one | Confirm the resource calendar is intended; otherwise Task |
| Type = WBS Summary | Every one | Delete unless the layout requires it and the spec allows |
| Type = Milestone, Duration ≠ 0 | Corrupt import or wrong type | Set correctly |
| Type = Milestone, no constraint, name contains "contract" or "KD" | Contractual date without its constraint | Add FOoB with reference; constraint register row |
Changing an activity from Task to LOE after progress exists resets its dates behaviour — do it in the baseline draft, not the live update, and note it in the change table.
🟥 Where people go wrong
- Tower crane as a 380-day Task. It shows float, fails the high-duration test and can never be statused honestly. LOE, spanning first lift to last lift.
- Curing as Resource Dependent. The labour resource's 6-day calendar decides when the concrete is cured. Task on a 7-day, 24-hour calendar; nothing else.
- Milestones with duration. An imported "Handover" with a 1-day duration is either a corrupt type or a Task pretending. Milestones are zero and typed as milestones.
- WBS Summary activities with logic requested. They cannot take it; a planner spends an hour discovering that. Delete them and let the WBS bands do the summarising.
- LOE with constraints or float reported. P6 doesn't allow the constraint and the float is not meaningful. If an LOE appears in a float report, the filter is missing the type exclusion.
- Changing type on a live activity. Type changes rewrite how dates are calculated; on a progressed activity that shows up as an unexplained date move in the next comparison. Baseline draft only, recorded.
⚖️ When you're challenged
"Why is site supervision not on the critical path? It's there every day." It's an LOE — its dates come from the work it supports, so it stretches with the project. If the critical path moves, supervision moves with it. Making it a Task would give it its own float and duration, and then it would be wrong every month.
"Add a predecessor to the Level 5 summary activity so the reviewer can see the logic." The Level 5 summary is a WBS Summary type, which P6 doesn't let hold relationships. The logic is on the activities under it — I'll switch the layout to show the WBS band with the logic lines visible, which is what the reviewer actually wants.
"Make the crane Resource Dependent so it follows the crane calendar." The crane itself is an LOE spanning its use. The lifts that need the 24-hour calendar are Task activities on that calendar directly — simpler, and the calendar is visible in the column rather than hidden on a resource.
📄 Related pages
- P6 Duration Types Explained — the second axis: what happens to duration when resources change
- Percent Complete Types — the third: how progress is earned
- Calendar Setup and Holidays — which calendar each type should carry
- DCMA 14-point assessment — why LOE and summary are excluded
- Milestones and Key Dates — contractual vs planning milestones
- Dangling Activities — SS/FF pairs on LOE and on production work
- Setting Up a P6 Project — the project default for new activities
✏️ Worked example
Type audit on a received subcontractor programme for an MEP package on a hospital in Jeddah — 1,240 activities:
| Finding | Count | Action | Effect |
|---|---|---|---|
| "MEP site supervision" as Task, 410 days | 1 | → LOE, SS from first fix L1, FF to T&C complete | Removed from float report; Metric 8 pass |
| "Scaffold – risers" as Task, 190 days | 3 | → LOE | Same |
| Curing of equipment plinths as Resource Dependent (labour resource, 6-day) | 6 | → Task, 7-day 24 h calendar | Each finished 1 day earlier; downstream equipment setting moved 1 day earlier |
| Milestones with 1-day duration | 14 | → Finish Milestone, 0 days | Handover chain shortened 14 days of false duration in aggregate; 4 days on the longest path |
| WBS Summary activities | 22 | Deleted; WBS bands enabled in layout | 22 fewer non-schedule activities; no date change (Schedule Comparison confirms) |
| LOE share after fixes | 1.9% of activities | Within convention | — |
Net effect on the package's forecast: completion 5 working days earlier than the sub reported, entirely from type corrections — and a note in the reconciliation table sent back to the subcontractor.
📖 References
- DCMA 14-Point Schedule Assessment, Metric 8 and general exclusions
- GAO Schedule Assessment Guide (GAO-16-89G), Best Practices 1, 2
- PMI Practice Standard for Scheduling, 2nd ed.
- AACE International RP 38R-06, Documenting the Schedule Basis
- Oracle Primavera P6 Professional User Guide — Activity Types; Level of Effort; Milestones; WBS Summary Activities (field labels as in P6 Professional v20; earlier versions differ)
From the field
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