Principles to determine the impact of weather delays on construction projects

Prepared by the Schedule Delay Analysis Standard Committee of the Construction Institute of ASCE, The American Society of Civil Engineers (ASCE) Schedule Delay Analysis, Standard ANSI/ASCE/CI 67-17 (ISBN (print): 9780784414361; ISBN (PDF): 9780784480861) “…presents guiding principles that can be used on construction projects to determine the impact of delays.”

Weather is one of the top three reasons for missed milestones and schedule delays in the construction industry and built environment, with negative impacts costing billions of dollars each year in the US to contractors, owners and operators. However, Schedule Delay Analysis uses ambiguous language about weather events and the subsequent impact of weather delays.


Excusable delays typically include third-party events, force majeure events, unusually severe weather, and owner-caused delays. Excusable delays mean that the contractor is entitled to a time extension for critical delay to a contractual completion date. Excusable delays may be non-compensable or compensable depending on the provisions of the contract. Typically, delays outside the control of both the owner and the contractor are excusable but non-compensable.

Given that adverse weather and weather events are “…outside the control of both the owner and the contractor…”, Schedule Delay Analysis, Standard ANSI/ASCE/CI 67-17 states that the delays are excusable but non-compensable, meaning that the owner may grant the contractor a time extension but not additional compensation, depending on the agreement between the owner and contractor.

Differentiating between “normal” weather and “severe” weather

However, Schedule Delay Analysis, Critical Path, 4.5 offers no definition of the term “severe” in the language about “…unusually severe weather…” Accordingly, how do the owner and contractor differentiate between normal weather or normal bad weather and “severe” weather, for a geo-location, season or month, as a part of weather delay and schedule delay analysis?

Further, the World Meteorological Organization (WMO, defines the term “severe weather” as “…any dangerous meteoroligcal phenomena with the potential to cause damage, serious social disruption, or loss of human life.” Accordingly, the definition by the WMO is generic, and lacks any specificity for the construction industry and built environment.

For example, high intensity rain events during the month of April in Boston can jeopardize the productivity of thermal and moisture protection work results, such as roofing and siding panels or membrane roofing, but high intensity rain events may not necessarily be “…dangerous meteorological phenomena…” as defined by the WMO and other weather agencies. 

More in the next blog post about schedule delay analysis, weather delays, weather planning, Weather Controls®, and weather risk management…

(Source: “Schedule Delay Analysis.” Schedule Delay Analysis | Standards, American Society of Civil Engineers,

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