Part 3 of a 4 Part Series on Incorporating Weather Days into Your Project’s CPM Schedule

By Mark Nagata & Bill Haydt

This article was first published on Trauner Ideas & Insights and is republished here with permission. Copyright © 2018 Trauner Consulting Services, Inc. All rights reserved.

2. Increase Durations of Weather-Sensitive Work Activities

A second way of accounting for or incorporating anticipated workdays lost to adverse weather into the project schedule is to increase the durations of the weather-sensitive work activities. This approach is as simple as it sounds. By simply increasing durations for activities that may be subject to adverse weather, those activities will then take into account the anticipated delay from that adverse weather.

For example, for a basic roadway project, a simple schedule is identified in Figure 4, below. This schedule does not take into account workdays that might be lost to adverse weather.


Assume that the contract for this project states that the contractor should anticipate losing 6 lost workdays in March, 5 lost workdays in April, 4 lost workdays in May, and 4 lost workdays in June. Using this approach, the anticipated lost workdays are simply added to the durations of the work activities that fall within those respective months (see Figure 5, below).


While this approach is probably the most direct way of ensuring that you’ve accounted for the anticipated workdays lost to adverse weather, it has several weaknesses. The first criticism is that the incorporation of adverse weather days in this manner is not always transparent and obvious. For example, it is not always obvious if and to what extent an activity’s duration was increased to account for time that might be lost to adverse weather. If transparency is important, the obvious solution to this problem would be to identify the number of workdays that represent adverse weather in the activity’s description or name.

The second criticism of this approach is the need to change the durations of the weather-sensitive activity durations when they are delayed from one month to another. For example, as identified above, the number of workdays lost to adverse weather can and does fluctuate from month to month. As such, when weather-sensitive work activities are moved or delayed from one month to another, which is common on construction projects, the durations of the weather-sensitive activities would need to be changed to reflect the number of anticipated adverse weather workdays in the new month within which the activity is now forecast to occur.

Said another way, if an excavation activity is delayed from March into April, there is a good chance that the number of anticipated workdays lost to weather in April is less than in March. If the activity’s duration includes anticipated workdays lost to weather in March, then when the excavation activity is delayed to April, it would be appropriate for the contractor to reduce the activity’s duration to reflect the anticipated number of workdays lost in April. However, this sort of change in an activity’s duration, to reflect the anticipated number of workdays lost to adverse weather when an activity is delayed from one month to another, is almost never done and on large projects would be difficult to maintain on a monthly basis.

Also, it is unusual for a contract to list the number of workdays a contractor should anticipate each month. Most contractors do not increase the duration of work activities based on the month the work is planned to be performed. Rather, they use a thumb rule. For example, one contractor client assumed that it would lose one workday in seven to adverse weather over the life of the project. Using this thumb rule, the contractor increased the duration of activities. Because the thumb rule was based on an average across the entire project, there was no need to adjust durations each month if the project was delayed.

Bill Haydt and Mark Nagata are Director, Shareholders of TRAUNER. Their expertise lies in the areas of construction claims preparation and evaluation, development and review of critical path method (CPM) schedules, delay analysis, training, and dispute resolution. They direct and perform all types of analyses from schedule delay analyses to inefficiency analyses and the calculation of damages.

Bill can be reached at

Mark can be reached at

More in the next blog post, Part 4 of a 4 Part Series on Incorporating Weather Days into Your Project’s CPM Schedule…

(Source: Nagata, Mark, and Bill Haydt. “Incorporating Weather Days into Your Project’s CPM Schedule.” Trauner Consulting Services,

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