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Time Impact Analysis for Weather Delay

7 replies [Last post]
Greg Paulson
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Hello, I have an in-progress activity that was delayed one day by bad weather. The Owner agrees that the weather stopped work and wants a Time Impact Analysis with a fragnet added that shows the forecast completion date pushed out by one day. Do I break the activity in two and put a single weather day activity in the middle of the two activities? Do I add the weather day with a FF relationship with the activity? Note that the schedule is setup where inclement weather was accounted for in the calendars, not as an activity at the end of the schedule. Thanks!


Zoltan Palffy
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perfomr a root caluse analysis and see what has caused the dealy during each month that you progress the schedule

It could be one of the items that you have listed. Typically one of these will be the root cause and will dirve the dealy for any given month of the update. Then create a matrix that list the update date, the total float during that update period, the root cause of the dealy, reference any scheduel nattative or other documentation that relates to the delay and who is responsible for that delay.

You can use your categories that you have listed if the delay falls into one of them,tWeather, Submittals, Request for Information and Site Differential 


Update Date #:  Date Date:  Total Float:  Root Cause:  Reference Document:  Responsible Party: 

Rafael Davila
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Planning for adverse weather in Construction Projects from hilalitani

My experience has been that specifications that reference NOAA are usually incomplete as they fail to state what constitute an above normal rain day.

The easy part is to figure out the average for days above certain threshold (in. per day) during the last 20 years for each but figuring out the threshold to use is arbitrary unless clearly specified.

The impact of a given threshold for different topographies is different and shall be selected accordingly. A one inch rain event at home means most rain will go directly to sea and little to land but in Texas and California a one inch rain event can be significant, not to mention the issue on intensity [rainfall/unit time] also matter.

At home experience shows the most common impact occurs close to 0.5 in.

Ironically it is not rain amount what is used for the day be considered impacted by rain, the rule is usually that at least during 50% of the work hours critical activities were impacted.

Ruel Camaquin
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Hi Master Zoltan,

It's been a awhile hearing from you, just too busy with work. I just like to know how to make a Time Impact Schedule that includes Weather, Submittals, Request for Information and Site Differential Report that causes delay and to used for possible claims?

Hoping you could give me the best possible inside in the matter and to the shortest period that we could make it. The project is still on-going, but this early the client and the construction management, request for us to prepare the said impact schedule.  Frankly, i have less experience or exposure about making a Time Impact Analysis or Delay Impact Schedule or waht ever it is called. Thanks.




Zoltan Palffy
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agree with Dave Always copy the project and them make the changes to the copied project

David Kelly
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Great question. Great answer from Zoltan.

I would add that ALL variations to a P6 plan should be in a separate project.  There are no restrictions to joining activities together in different projects. 

This means if we open the “base” project only, and change the scheduling options to “ignore relationships to and from other projects” – we can always see the result of the schedule without variations.

Greg Paulson
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The schedule updating process is a month behind, so August hasn't been submitted.  Because it is a critical activity, I think Option #3 of inserting it as a successor will be the clearest for the Owner to review. 

Thanks so much.

Zoltan Palffy
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just so that I understand you included the planned monthly anticipated adverse weather days by month into your calendar. Lets say that for this example we wil use the month of August. So the  the planned adverse weather days during the month of August were anticipated to be 5 days. You actually experienced 6 days of adverse weather to activites that were on the critical path. This means that 6 actual adverse - 5 planned adverse = 1 day that you are owed as a non compensable time extension.

The answer to this question depened on how or if you have already updated your schedule for the month that you experienced the 1 day of adverse weather above the normal anticipated adverse weather. 

There are several ways to do this.

Schedule already updated through August

If you have already updated the schedule through the month of August means that in effect you have already captured this delay becasue lets say a 5 day activity on the critical path actually took you 6 days to do becasue the 1 extra day of weather. This would be reflected in the actual start and finish dates.

change the project must finish or the project milestone finish on or before date by 1 day and modify the milestone activity name and add "REVISED to dd/mm/yy based on adverse weather during August. 

Schedule NOT updated through August 

Option #1 add a 1 day activity and insert it as a SUCCESSOR to the project completion milestone and call it Adverse weather during August 2018 and then add a New Milestone call it revised project completion based on adverse weather.

Option #2 add a 1 day activity and insert it as a predecessor to the project completion milestone cal it adverse weather during August. Make sure to connect its predcessor an activity that is driving and critcal.

Option #3 add a 1 day activity and insert it as a SUCCESSOR to the activity that it actually happened to. for example if it was excavation then insert a new 1 day activity called adverse weather during August. Make its predcessor the excavation activity and make its successor whatever the successor  to the excavation was. The problem with this method is that is is sort of Planning and actualizing weather all in the same update. 

points to remember

  • whatever you do make sure to change the project must finish by date if you are using it and or the last activity mielstone finish on or before date by 1 day.
  • if inserting a  NEW activity make sure that the predcessor and successor is driving and critical.
  • Use the notebook function to document what you have done and why you have done it.