In order to understand exactly how weather can disrupt the schedule of construction projects, we need to outline the schedule process and the elements of it. KBS projects are organized into a sequence of activities, based on the fixed number of days from a Notice to Proceed through project completion, which result in a series of Critical Path Activities that must be completed on time. Without the first Critical Path Activity, the second cannot be completed, and so on.
Considering these Critical Path Activities, we must take into account the actual weather, which affects construction projects in many different ways, depending on a variety of things:
- Type of weather –rain, snow, or extreme cold
- Type of construction project – inside, outside, scale
- What stage the project is in – if the roof is on, weather has less impact
- Owner preferences
KBS Project Managers review National Weather Service historical data in order to create realistic schedules for their teams. Using scheduling software such as Microsoft Project or Phoenix CPM, the KBS PMs randomly choose a few days per month to be “non-work days” in order to build Float, nebulous time allowed for delays such as weather events. To clarify, the month of April has 30 days, averaging 22 work days. Anticipating rain and/or snow, PMs subtract the two non-work days that allow a total of 20 days in the month of April for the construction schedule. If a weather event occurs, then the non-work day is Actual. If there is no event, the team is ahead one day, generating the Float.
Type of Weather
Rain vs. Snow
Rain is a one-time occurrence. Snow lasts and melts, then refreezes, then melts again, putting the schedule even further behind. If there is no Float left, then Critical Path Activities are impacted and a ripple effect occurs. The ground is in a constant muddy state, and solutions are limited and challenging. Construction sites need to have access for material deliveries and emergency vehicles, and maintaining site access, as well as the building areas, proves to cause delay and expense.
The PM can:
- Limit the areas of equipment movement and set a confined space for work.
- Place hardwood timber mats that can support the weight of heavy equipment and trucks.
- Shut down the job.
On the bright side, if it snows when it’s below freezing beforehand, the ground is frozen, therefore solid, and not a matter of concern.