Schedule Basis Memorandum
Last reviewed 9 September 20261,754 words8 min read
The document that protects you eighteen months later
🟩 In one line: The schedule basis memorandum (SBM) records what you assumed when you built the programme — calendars, productivity, crew sizes, method, sequence, procurement dates, access, interfaces, exclusions — so that when a date is questioned eighteen months later, the answer is on paper and not in the head of a planner who has left.
👤 Who this is for: Mid-level planners building a baseline; juniors asked to "write up the basis"; seniors deciding what a claim will need to prove. You should know the duration formula (crew-and-manhour-formulas) and what a Level 3 baseline is.
First, let's be honest about why this page exists
Every baseline is built on a few hundred assumptions. Most of them are never written down. Eighteen months later the project is late, the client says "your programme was unrealistic", the original planner is on another job, and nobody can say whether the 22-day duration for Level 12 slab was based on a 12-man crew, a 16-man crew, or a guess.
A basis memorandum costs two days at baseline stage. Without it, every delay argument starts from zero; with it, the argument starts from the accepted assumption and asks only what changed.
🟨 The standard — what "good" looks like
| Source | What it says (paraphrased) |
|---|---|
| AACE RP 38R-06, Documenting the Schedule Basis | Defines the SBM: scope, assumptions, methodology, constraints, exclusions, risks and the data used, recorded at baseline and kept current |
| FIDIC 2017 Cl 8.3 (check the edition in your contract) | Programme to be accompanied by a supporting report describing methods, stages, resources and personnel — in practice the SBM plus narrative |
| NEC3/NEC4 Cl 31.2 | Programme to show a statement of how the Contractor plans to do the work, principal equipment and resources, time risk allowances and float |
| SCL Protocol 2nd ed., Core Principle 1 and Part B Guidance | Programme should be supported by a method statement and records sufficient to understand how it was built |
| PMI Practice Standard for Scheduling, 3rd ed. | Schedule model documentation as a required component of the schedule model |
| GAO Schedule Assessment Guide, Best Practice 1 (capturing all activities) and Best Practice 10 (documenting the schedule) | Basis documented well enough for an independent reviewer to reproduce the logic |
🟢 Rule to remember: if a reviewer with no site knowledge can rebuild your durations and sequence from the SBM alone, it's finished. If they'd have to ask you, it isn't.
How it actually works
What goes in. The SBM is a numbered document, 15–40 pages for a typical building or infrastructure job, mostly tables. It is issued with the baseline and revised only when the baseline is revised.
| Section | Content | Typical length |
|---|---|---|
| 1. Scope and documents | Contract scope; drawing/spec revisions used; BOQ revision; tender programme reference | 1 page |
| 2. Key dates | Commencement, sections, milestones, completion; source clause for each | Table |
| 3. Programme structure | Level 3 as contract baseline; WBS logic; activity count; coding; how L4 will be derived | 1–2 pages |
| 4. Calendars | Each calendar: days/week, hours/day, holidays, Ramadan hours, summer midday break, curing calendar | Table |
| 5. Method and sequence | Construction method per element; zoning; crane strategy; pour sequence; vertical vs horizontal logic | 3–6 pages |
| 6. Duration basis | Quantities, unit rates, crew sizes, productivity factors per major activity type; the formula used | Table, longest section |
| 7. Resources | Peak manpower, key equipment, assumed mobilisation curve | Table + histogram reference |
| 8. Procurement and long-lead | Item, approval duration assumed, lead time, delivery date, required-on-site date | Table |
| 9. Employer / third-party dependencies | Access dates, IFC drawing release, free-issue material, authority approvals, utility connections | Table with assumed date |
| 10. Constraints | Every constraint in the file, with reason (only SOoA and FOoB survive) | Table |
| 11. Float and risk allowance | Terminal float, time risk allowance, where contingency sits, who owns it | 1 page |
| 12. Exclusions and assumptions | What the programme does not include; weather assumption; shift assumption | Bullet list |
| 13. Risks | Top schedule risks and their treatment | Table |
| 14. Revision log | Version, date, what changed | Table |
The duration basis table is the core. One row per activity type (not per activity). The activity-level basis line lives in P6 UDFs or Notebook and points back to this table.
| Activity type | Unit | Rate basis | Crew | Hours/day | Factor | Source |
|---|---|---|---|---|---|---|
| Slab reinforcement | t | 0.12 mh/kg | 14 steel fixers | 10 | 1.10 summer | Company norms 2023 |
| Blockwork 200 mm | m² | 0.9 mh/m² | 8 masons + 4 helpers | 10 | 1.00 | Tender estimate |
| Ductwork installation | kg | 0.25 mh/kg | 6 fitters | 9 | 1.05 | Subcontractor submission |
How it links to P6. Each calendar in Section 4 is named identically in the file. Each constraint in Section 10 matches the P6 constraint list. Each procurement item has an activity ID. A reviewer should be able to go SBM → P6 → SBM without a gap.
When it changes. Revise it with every approved baseline revision and with any recovery schedule that changes method. Do not revise it for monthly updates — those are for the narrative (schedule-narrative).
📜 Why it matters contractually
| Situation | Without SBM | With SBM |
|---|---|---|
| Client says duration was unrealistic | Argument about what "reasonable" means | Point to the accepted rate and crew; ask what evidence contradicts it |
| Employer delivers access 6 weeks late | You must first prove what access date you relied on | Section 9 states it; TIA starts from there |
| Productivity claim (disruption) | No planned rate to compare against | Planned mh/unit is the measured-mile baseline |
| Programme accepted, then challenged | Acceptance covers bars only | Acceptance covered the stated basis too |
| Planner leaves | Basis leaves with them | Document stays |
🟥 Where people go wrong
- Writing it after the baseline is accepted. It becomes a justification, not a basis, and reviewers can tell. Build it alongside the programme; the duration table is the working document you use to build durations anyway.
- Listing assumptions without dates or numbers. "IFC drawings assumed timely" protects nobody. "IFC structural drawings for Zone A assumed by 14-Mar-25 (activity ENG-1040)" does.
- Making it a narrative essay. A 60-page prose document nobody reads. Tables, numbers, activity IDs. Prose only in method and sequence.
- Hiding contingency. Saying "no float allowance" while padding durations by 15% is discovered in the first productivity check. State the allowance, where it sits, and under which clause it's owned (buffers-and-contingency).
- Not matching the P6 file. SBM says 6-day 10-hour calendar; the file has 8 calendars including a 7-day one on structure. The mismatch is the reviewer's first comment and undermines the rest.
- Never revising it. Baseline Rev 2 was accepted with a different crane strategy; SBM still describes Rev 0. Now the accepted basis is unknown again.
⚖️ When you're challenged
"Why do we need this? The programme is the programme." "The programme shows the dates. This shows why the dates are what they are. When someone asks in a year whether 22 days for a slab was reasonable, this is the only thing that answers."
"Your durations are too long — what are they based on?" "Section 6, table 6.3. 340 tonnes at 0.12 manhours per kilo, 14 fixers, 10-hour days, summer factor 1.10 — 22 days. If the client has a rate that says otherwise I'll look at it."
"You've stated an access date we never agreed." "It's the date in Appendix A to the contract, and it's the assumption the programme was built on. If access is later, the programme moves; the SBM is telling you that now rather than later."
"This is just a way of setting up claims." "It's a way of setting up clarity. It protects both sides — if we're slower than our stated rate, that's on us and you can see it."
📄 Related pages
- Justify a Duration — the activity-level version of Section 6
- Crew and Manhour Formulas — the formula the duration table uses
- Schedule Narrative — the monthly document; different job
- Baseline Approval and Control — getting the SBM accepted with the programme
- Buffers and contingency — declaring float and time risk allowance
- Procurement and Long-Lead Items — Section 8 in full
- Time Impact Analysis — where the SBM's stated dependencies get used
✏️ Worked example
A mid-rise residential block in Dubai. Baseline accepted with SBM Rev 0. Fourteen months in, the Engineer rejects an EOT claim for late IFC MEP drawings, saying the contractor's structure was already behind so the drawings were not critical.
| Item | SBM Rev 0 states | What happened | Result |
|---|---|---|---|
| IFC MEP drawings, Levels 1–8 | Assumed 30-Apr-24 (Section 9, item 9.4, activity ENG-2210) | Received 25-Jun-24 | 56 days late — undisputed |
| Structure progress at 30-Apr-24 | Level 5 slab planned complete | Level 5 slab actually complete 08-May-24 | 8 days behind |
| MEP rough-in start, Level 1 | Driven by IFC + 14-day approval (SBM 6.7) | — | Drawings, not structure, drove it |
| Slab cycle basis | 7 days/floor, 16 carpenters, 10 h (SBM 6.2) | Achieved 7.4 days average | Close to basis; contractor delay minor |
Because the SBM showed structure was only 8 days behind against a 56-day drawing delay, the concurrency argument collapsed to 8 days. 48 days awarded. Without the SBM, the contractor would have had to reconstruct the planned relationship between structure and drawings from memory.
📖 References
- AACE RP 38R-06, Documenting the Schedule Basis
- FIDIC 2017 Cl 8.3; FIDIC 1999 Cl 8.3 (check the edition in your contract)
- NEC3 / NEC4 ECC Cl 31.2 (check the edition in your contract)
- SCL Delay and Disruption Protocol, 2nd ed. (2017), Core Principle 1; Part B Guidance
- PMI, Practice Standard for Scheduling, 3rd ed. — schedule model documentation
- GAO, Schedule Assessment Guide (GAO-16-89G), Best Practices 1 and 10
From the field
Experience from working planners. Unreviewed — read it as experience, not guidance.
Add what you know about schedule basis memorandum. What worked, what the consultant pushed back on, what you would do differently next time. A paragraph is plenty.
Contributors get their name and one link on the site — your own templates, course or consultancy. We take nothing and hold nothing.
Add your experience