Planning & Accounting for Adverse Weather
Weather delay is usually excusable but non-compensable — time, not money. Split the weather into normal (your risk) and abnormal excess, then test whether that excess hit the critical path. Built on AACE 84R-13.
Why weather is a special kind of delay
Weather delays are usually excusable but non-compensable: the contractor gets more time, but not more money. Why? Because weather is nobody's fault — the owner didn't cause it, so they shouldn't pay for it; but the contractor shouldn't bear liquidated damages for an act of nature either. So the typical remedy is a time extension only.
Building the weather baseline
To know what's abnormal, you first define "normal" — and you do it before the work, from historical data, not from hindsight. The standard source is long-run climate records (e.g. NOAA in the US) for the project's locale: the typical number of lost days per month from rain, temperature, wind, or other thresholds that actually stop the work in question.
Two pieces make the baseline usable: the anticipated lost days per month (from history), and the work-stopping thresholds (how much rain, or what temperature, genuinely halts this activity — concreting, earthworks, and steel erection have different limits). Bake the anticipated days into the schedule as planned non-work days, and a fair baseline is in place from day one.
The abnormal-weather test, then the critical test
Recovering time for weather is a two-stage test. Clearing the first stage is necessary but not sufficient.
| Stage | Question | If "no"… |
|---|---|---|
| 1 · Abnormal? | Did actual adverse days exceed the historical baseline for that month? | No excess → no claim |
| 2 · Critical? | Did the abnormal excess actually impact critical-path work and delay completion? | No critical impact → no extension |
Worked example — abnormal excess in one month
Earthworks (a critical-path activity, stopped by rain) ran through a single month. Compare actual lost days to the baseline.
From baseline to excusable days
Worked example| Step | Value |
|---|---|
| Historical baseline rain days (this month) | 6 days |
| Actual work-stopping rain days | 14 days |
| Abnormal excess = 14 − 6 | 8 days |
| Of which fell on critical-path earthworks | 8 days |
The first 6 rain days were "normal" — the contractor's risk, already in the bid. Only the 8 abnormal days, and only because they hit critical earthworks, support an extension. Note the relief is time, not money: no prolongation cost for ordinary weather delay unless the contract says otherwise.
Abnormal-weather calculator
Set the historical baseline, the actual work-stopping days, and the share that hit the critical path.
Excusable weather days
Try it yourselfSet the historical baseline, the actual work-stopping days, and the share that hit the critical path.
Ten things to remember
- Weather delay is usually excusable but non-compensable — time, not money.
- The contractor owns "normal" weather; the owner risk is the abnormal excess.
- Define the baseline up front from historical climate data — not in hindsight.
- Set work-stopping thresholds per activity — concreting, earthworks and steel differ.
- Bake anticipated weather days into the schedule — good control and claim foundation.
- Stage 1 — abnormal? Actual adverse days must exceed the baseline.
- Stage 2 — critical? The excess must hit critical-path work to move completion.
- Abnormal but non-critical weather earns nothing — float absorbs it.
- Keep daily weather records — actual conditions, what stopped, which activity.
- Read the contract — some shift weather risk or define abnormal explicitly.
Glossary
- Abnormal weather
- Adverse weather exceeding the historical baseline for that location and season.
- Anticipated lost days
- Normal weather days built into the baseline schedule as planned non-work days.
- Critical-path test
- The requirement that abnormal weather hit critical work to justify an extension.
- Excusable delay
- A delay that entitles the contractor to a time extension (relief from liquidated damages).
- NOAA / climate records
- Long-run historical weather data used to set the baseline.
- Non-compensable
- A delay that earns time but not money — the typical weather outcome.
- Weather baseline
- The historically expected adverse days per month, defined before the work.
- Work-stopping threshold
- The condition (e.g. rainfall, temperature) that genuinely halts a given activity.