Writing down the assumptions your plan depends on
In the first week on site, the project manager reads the estimate for a two-storey animal shelter line by line. There is no temporary heat, and a note in the margin says "closed in before Dec." The schedule shows the owner approving every finish submittal in ten working days, and nobody has asked the owner whether that is realistic.
Write each assumption behind the schedule and budget as a statement you can check, with the date by which you will know and the person who checks, and review the list until each one is confirmed or has failed. A risk is an event that may happen; an assumption is something the plan already treats as true, so a risk register rarely lists it. The US Department of Energy defines assumptions as factors used for planning that are "considered true, real or certain", and notes that they generally contain an element of risk. The US Government Accountability Office expects those behind a reliable estimate to be "clearly identified, explained, and documented"; left in an estimate's notes and never checked, they fail silently.
- Collect them at the estimate handover: ask the estimator and the scheduler what they took as true about productivity, weather, deliveries, ground, access, permits and approval times.
- Make each one checkable: "roof and windows closed in by 1 December", not "normal winter conditions".
- Note what rests on it: the activities, cost lines and amounts that hold only if it does.
- Give each a check date and an owner: the day you will know, and who will look.
- Review the log every two weeks, marking each line confirmed, at risk or failed.
- Act promptly on a failure: re-plan, re-price, tell the owner, and log any new risk. Follow contractual notice deadlines immediately; do not wait for the next review.
Common mistakes
- Writing assumptions so vaguely that they can never be shown to be wrong.
- Keeping the log in the estimate file, where the site team never opens it.
- Checking an assumption only after it has already failed.
- Marking a line failed but leaving the schedule and budget unchanged.
Action list
Start the log today
- Read the estimate's notes, margins and qualifications
- Ask the scheduler which durations came from the last job
- Ask the owner how long approvals really take
- Put a number and a date in every assumption
- Keep the log beside the risk register, not inside the estimate
Check your understanding
The estimate assumed the drywall crew would board 110 m² a day, as on the last job. Is that a risk or an assumption, and how would you handle it?
