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How to Incorporate Weather Days in Your Construction Schedule

If you're a construction manager, you know that the weather can hugely impact your schedule. Weather conditions can change dramatically and quickly, particularly in the UK, from sunny skies and summer temperatures of 30 degrees Celsius, to pouring rain and 12 degrees the very next day.

So how do you deal with these sudden changes in the weather? One way to incorporate adverse weather into your construction schedule is by using weather days.


Weather days in construction schedule

A weather day is essentially a day that has already been budgeted in the contract as a disrupted day that you can use to account for expected bad weather. For example, in the winter months you would expect more rainy days. If you endure a few rainy days in February then it's expected that you will have already accounted for this in your contract and your plan.

If you have numerous rainy days in summer then it’s less likely you have accounted for this. You might have spare float you can use, or it may cause a delay.    

Using weather delay days can help keep your construction schedule on track, no matter what the weather throws at you. However, although you should expect weather impact, it can also do the unexpected.

If there are an extraordinary number of rainy days then this could fall outside the remit of expected weather, and this is where your contract might kick in to allow for some extra time and or money. To learn more about how construction contracts deal with weather read our article here.      

The schedule is usually prepared using the critical path method and visualised using bar charts or Gantt charts.

Schedule with the critical path method using bar charts or Gantt charts

(Image source:

However, construction professionals have long debated how weather days should be incorporated into a project schedule. While there isn't a perfect solution, there are three common approaches to dealing with schedule delay analyses:

  1. Adding non-work days to the work calendars to show which workdays might be lost due to inclement weather.

  2. Representing workdays that might be lost to bad weather by increasing the duration of weather-sensitive work activities.

  3. Adding an “adverse weather” activity to the project schedule with a duration equal to the anticipated weather-related workdays.

Let's discuss each of these three approaches in more detail below.

Adding inclement weather workdays in work calendars

How it works

In this approach, adverse weather days are added to the work calendars used for scheduling. This means that these weather-related workdays will not be available for assigning tasks to the project schedule.

Advantages of this approach

One advantage of this approach is that it accurately represents available workdays for tasks to be completed. It also helps in identifying potential risks and consequences of weather delays, allowing the team to plan accordingly.

Criticisms of this approach

The main criticism is that no one can tell with 100% certainty what the weather will be on a given day and if it will be severe enough to stop work. This approach may lead to the overestimation of weather-related workdays, resulting in excessive buffer time and potentially longer project duration.

Representing weather-related workdays by increasing weather-sensitive tasks

How it works

In this approach, weather-sensitive tasks such as pouring concrete or laying asphalt have their durations increased to account for weather-related workdays. This allows for a more fluid project schedule, as weather delays can be accounted for without adding specific weather days to the work calendar.

Advantages of this approach

This approach allows for a more flexible project schedule, as weather-related delays can be accounted for without adding specific weather days to the work calendar. It also helps prevent the overestimation of weather-related workdays.

Criticisms of this approach

One criticism is that not all tasks are weather-sensitive and may not need to have their durations increased. This approach also requires a more in-depth understanding of weather patterns and potential weather delays for each weather-sensitive task.

Adding an adverse weather activity to the schedule

How it works

Rather than including anticipated adverse weather days in the work calendars or durations of weather-sensitive activities, adding an "Anticipated Adverse Weather" activity at the end of the schedule before the project's completion milestone would better represent all required anticipated adverse weather.


Advantages of this approach

This approach allows for a more accurate representation of weather-related workdays as the duration can be adjusted as weather patterns, and forecasts are updated. It also allows the team to plan additional work during good weather days to compensate for lost time due to weather delays.

Criticisms of this approach

A major issue with this method is that on long-term projects, the schedule would list all bad weather days in the end rather than factoring them throughout. For example, if we looked at work being done in year two or three, it would be scheduled to start much earlier than expected because there was no mention of adverse weather conditions during the first year.

This issue might be a problem depending on the project type and duration. Additionally, this approach requires continuous monitoring and updating of weather patterns and forecasts to ensure the "Anticipated Adverse Weather" activity is accurately represented.

Luckily there is a statistically correct and accurate way to incorporate weather days into a schedule. This uses calendars for every type of impacted activity and assigning probabilities of impact for every 3 day window of time. By putting this probabilistic data into a calendar it allows plans to move and change and for the weather impact to update automatically. it also does not state a specific day will be impacted, just that there is a potential for impact.

Doing this by hand would be incredibly time consuming so although it is the most accurate way without a tool to assist no planner would have the time or will power to achieve this.    

Weather delay days: EHAB Weather Risk Management Platform

Luckily, utilising a platform such as EHAB Weather Risk Management can allow you to achieve the best in class weather risk incorporation into your schedule. The platform will allow you to achieve this in 10-30 minutes, rather than the days it might take to achieve it by hand. EHAB offers accurate forecasting and proactive planning for weather sensitive work activities in all your construction projects.

This platform offers hyper-local climate data, real-time and historical weather information, and relevant warnings to ensure construction planning accounts for potential adverse weather. It also allows for easy checking of how changing plans will be affected by weather and modelling based on your project plan.

With access to 2-week forecast data tied into your plan, EHAB Weather Risk Management can assist in ensuring weather delays are accurately accounted for and planned for in your construction schedule.

Schedule a free 30-minute demo today to see how this platform can benefit your construction project's success.


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