Construction Weather Delays: What Counts, How to Document Them and Concrete Weather Limits

What counts as a weather day

Contracts differ, so start with the clause. On federal fixed-price construction work, the default clause (FAR 52.249-10) lists unusually severe weather among the causes of excusable delay, and requires the contractor to notify the contracting officer in writing of the causes of delay within 10 days of the beginning of the delay, unless the officer extends that period.

There is no single industry definition of abnormal weather. Kevin O'Beirne, writing as vice chair of the Engineers Joint Contract Documents Committee (EJCDC), says that what is typical and what is abnormal are subjective, and suggests using weather data for the vicinity of the site, such as monthly averages of rain, snow and extreme temperature days, as the baseline. He also notes that many parties would argue that some time lost to weather is normal and belongs in the construction schedule from the start.

That points to a practical rule: write the definition into the contract. For example, "a weather day is a day when more than [__] inches of rain is recorded at [named station], or wind at the site exceeds [__] mph during planned crane work." The numbers here are placeholders for you and your owner to agree, not recommended values.

How to document weather delays

Do the logging the same day, while it is fresh. A useful daily entry records:

• The work planned for the day and the crews scheduled.
• The weather at the site: rain or snow amounts, temperatures, wind, and the times weather stopped and restarted work.
• The work actually done and the work lost, by task and crew hours.
• The effect on the critical path, and any notice sent, with the date.
• Photos with timestamps.
• The forecast that was in effect the day before, since a storm that was forecast is harder to call unforeseen.

Then compare against normals. NOAA's NCEI climate normals are 30-year averages (the current set covers 1991 to 2020) and include monthly and daily averages of temperature, precipitation and other variables from thousands of stations. A simple monthly table makes the case clear:

Name the station, its distance from the site and the source of every number. When the stakes are high, a forensic weather report reconstructs conditions at the address for the dates in question. WDS prepares them for construction schedule disputes, delay claims and force majeure notices, signed by a degreed meteorologist and quoted per request.

Concrete in cold weather

A National Institutes of Health technical bulletin summarizing ACI 306R-16 gives the key points. Cold weather concreting conditions exist when the air temperature has fallen to, or is expected to fall below, 40°F during the protection period. Concrete should be protected from freezing until it reaches a compressive strength of 500 psi, which is about two days after placement for most concrete maintained at 50°F. Below 40°F the hydration reaction slows and the concrete stops gaining strength. Concrete that freezes at an early age can lose up to 50 percent of its ultimate strength.

• The limits apply to concrete temperature, which is measured under ASTM C1064. Air temperature alone does not tell you.
• Keep surfaces in contact with the concrete free of ice and snow and above freezing.
• Schedule the pour for the warmest part of the day, and use insulating blankets or heated enclosures.
• Monitor and record the concrete surface temperature, because it shows how well the protection is working.
• Look up recommended concrete temperatures at placement in Table 5.1 of ACI 306R-16 and in your specifications.

Concrete in hot weather

ACI 305 defines hot weather concreting as any combination of conditions that impair the quality of fresh or hardened concrete by speeding up moisture loss and cement hydration. The Tennessee Department of Transportation's best practice guide lists the causes as high temperatures, high winds, low relative humidity and solar radiation, and the effects as plastic shrinkage cracking, faster slump loss, quicker set and thermal cracking.

TDOT tells inspectors to make sure protective measures are in place when the evaporation rate exceeds 0.2 pounds per square foot per hour, estimated with the ACI nomograph from air temperature, relative humidity, concrete temperature and wind speed. Maximum concrete temperature is set by project specifications. TDOT's specification caps it at 90°F, while a STRUCTURE magazine review notes that ACI 305R itself does not give maximum temperatures for hot weather placement. Other practices TDOT lists include scheduling pours for night or early morning, shading and cooling materials, dampening forms, and starting curing as soon as the water sheen disappears.

Cranes, wind and lightning

OSHA's crane standard (29 CFR 1926.1417) does not set a wind speed. It requires employers to follow the manufacturer's procedures and the competent person to adjust equipment or operations for the effect of wind, ice and snow on stability and rated capacity. So the number that stops a lift comes from the crane's manual. OSHA treats lightning separately, in a fact sheet on outdoor work that the guide to lightning policies summarizes.

Using site forecasts to avoid the delay

Records explain a delay after the fact. Planning prevents some of them. With 4070 for business, WDS gives construction teams site-level forecasts for pour windows, crane wind thresholds and daily site risk, with alerts for wind, lightning, heat and heavy rain, and a meteorologist who can explain the timing to the owner and subcontractors. See the construction solutions page.

Frequently asked questions

Sources

Sources checked October 6, 2026. ACI documents are copyrighted. This guide relies on the public summaries listed here, so consult the current ACI documents and your specifications.

1. Acquisition.gov, FAR 52.249-10 Default (Fixed-Price Construction)Unusually severe weather as an excusable delay and the 10-day written notice.
2. Kevin O'Beirne, Force majeure events: abnormal weather and uncontrollable delays on a construction project, Engineers Joint Contract Documents Committee (EJCDC)No industry standard for abnormal weather, historical data from the vicinity as a baseline, and normal weather in the schedule.
3. NOAA NCEI, U.S. Climate Normals30-year averages, the 1991 to 2020 period, and station coverage.
4. National Institutes of Health, Office of Research Facilities, Cold Weather Concreting technical bulletin (April 2021, PDF)Summary of ACI 306R-16: 40°F definition, 500 psi, strength loss from early freezing, concrete temperature.
5. Tennessee Department of Transportation, Hot Weather Concreting Best Practices (PDF)Causes and effects of hot weather, the 0.2 lb per square foot per hour evaporation trigger, and TDOT's 90°F limit.
6. Cawsie Jijina, Cold and Hot Weather Concrete, STRUCTURE magazine (September 2017)ACI 305 definition of hot weather concreting, and that ACI 305R does not give maximum concrete temperatures.
7. OSHA, 29 CFR 1926.1417 Operation (cranes and derricks in construction)Manufacturer procedures and adjusting operations for wind, ice and snow.

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