What are the odds the rain costs you the date?
A schedule that works at average weather misses in the bad seasons. Draw the lost days per week from a discrete weather table and the deadline risk becomes a number you can negotiate with.
Construction Starter Monte Carlo Pro engine
After you install, this is the model to open.
Will the Weather Blow the Deadline?
- In your spreadsheet, click the Sortia icon in the strip of icons down the right-hand edge. No strip? Click the arrow at the bottom-right to open it. You can also use Extensions, then Sortia, then Open Sortia.
- Click Start from a template and put that name in the search box.
- Pick the card with that name and click Load this template. It arrives on a new tab with real numbers already in it.
This one runs on a Pro engine, and every free install includes five full-quality runs on your own numbers, shared across all five Pro engines rather than five for each. After that, Pro is $199/year.
The answer
Twenty thousand simulated seasons:
- Mean duration
- 8.2 weeks
- P95 duration
- 15 weeks
- Deadline blown
- 30% of trials
The comfortable-looking eight-week plan fails almost one season in three. Move the deadline to ten weeks and rerun: the risk collapses, and the difference is what the weather float is worth in the negotiation, priced instead of argued.
The model
Thirty workable days needed, five working days a week, and a weekly draw: 35% lose none, 35% lose one, 20% lose two, 10% lose three, straight from a regional climate table.
| Workable days needed | 30 |
| Weather loss per week | discrete: 0/1/2/3 days |
| Deadline | 8 weeks |
| P(blown deadline) | simulated |
Once it is in your sheet
- The model arrives with real numbers in it and runs as it stands, so you can press the button first and understand it second.
- Change the numbers to yours. The sheet marks which cells are inputs and which hold formulas, and most labels carry a note explaining the row.
- Press the run button at the bottom of the panel. It is labeled for the tool you are in, and the result lands on its own tab, with a written reading of it beside the figures.
Never used Google Sheets? Start here goes the whole way, in seven steps, and assumes nothing.
Next question
- What is finishing on time actually worth?What Do Late Days Really Cost?
- When does the punch list actually finish?Is Closeout on Track?
- What do the lean, normal and cautious bids each look like?Three Ways to Price This Bid
- Cheapest crew per site, or cheapest week?Which Crew Goes to Which Site?
- The rate says 90 a day. What do the site records say?What Does a Normal Crew Day Produce?
- Are you paying for cement the spec does not need?Which Concrete Mix Meets Spec for the Least Money?
Every model like this one, and the method behind them: Monte Carlo simulation.