Construction Planning and Scheduling
Introduction Construction activities are often exposed to various weather conditions, and often construction productivity is dependent on these weather conditions. Weather conditions are local, seasonal, and sometimes unusual. Inclement weather conditions often result in project disruptions, delays, and disputes between the project parties.
Many trades such as earthwork, concrete, roofing, and landscaping are often affected by severe weather, meanwhile other trades such as carpet installers or sheetrock installers may not be directly affected by the weather.
Owners, general contractors, and subcontractors all face many risks associated with weather conditions. In order to mediate weather risks, all of the involved construction parties adopt various strategies; purchase insurance, and contract options. Typically project owners try and allocate the risks related with weather delays by adding weather clauses in the contract provisions. The goal of this paper is to discuss the impact of weather delays in construction projects. A construction schedule should include a developed plan to allow for adverse weather. The weather considerations should be addressed during contract negotiation.
By accounting for weather integration in the contract and in the baseline schedule owners and the contractor can reduce the risk of disputes from weather impacts and avoiding the rejection of claims dealing with unforeseeable or unusually severe weather. Most contracts nowadays have integrated weather calendars in the schedule. Adverse Weather Adverse weather, commonly referred to as severe weather, is any weather condition, rain, snow, temperature that exceeds historical data gathered over a specific period of time to establish what could be reasonably expected over the course of the construction project.
Establishing unusually severe weather can be a challenging task. The most common method is to compare the actual weather experienced on the project to a historical normal for the same location. By using historical data a normal or expected level of severe weather can be established for a given time period. (Long 2010) Normal Weather Severe weather conditions should be incorporated in all construction contracts and in the contract it should specify the difference between normally and abnormally severe weather conditions.
In contracts today, it is normal for some owners and contractors to provide the anticipated number of weather days in today’s contracts. The contracts now specify the average number of adverse weather days for certain project locations. It is in the best interest of projects to identify weather statistics, and contracts should provide the number of anticipated weather delay days based on those statistics. Temperature Temperature is well defined in construction contracts. The standard specifications in a contract include the minimum and maximum temperatures for many construction materials.
However, temperature directly affects the productivity of workers. Most construction materials have thresholds. However, temperature is a type of weather effect in which construction does not necessarily have to be delayed when exceeding these thresholds, as long as the project can absorb expenditures for controlled measures such as heated enclosures. Wind Wind can affect certain construction operations, but the effect of wind on temperatures is equally important. The combination of low temperatures and wind causes wind chill, which can reduce productivity and can even be dangerous to workers.
Wind alone can force several construction activities to shut down, for example high winds can make cranes unstable, which could lead to accidents. High wind also may cause fresh concrete to dehydrate on the surface. Wind not only affects the temperature and construction activities such as crane work, but wind also affects materials and material processes. Soil Temperature Soil temperature does not directly affect labor productivity, but it does have an effect on operations and equipment. The biggest impact of soil temperature is on earthwork. Frozen ground magnifies the difficulty of movement and compaction of soils.
Frozen soil conditions greatly reduce the equipment productivity. As cold weather affects the operator of the equipment, the soil conditions affect the effectiveness of the equipment. Weather Delay Day What type of weather qualifies as a weather delay day? A weather delay day is a day in which work must be completely stopped because efficient construction operations will be difficult to achieve with the weather conditions. Three key factors affecting weather delays and disruptions are; type of construction, on-site drying conditions, and the intensity of rainfall.
The threshold values for adverse weather vary from location to location. The threshold values also depend on the trades working and various other social and natural factors. However, a weather day should be decided based on the combination of the threshold values, type of work affected, and common sense. Table 1 below shows a sample adverse weather day calendar. (Glavinich n. d. ) Table 1: Sample Adverse Weather Allowances MonthJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC Adverse Weather Days665452245544 Weather Calendars Once threshold values are determined, the adverse weather days can be incorporated into the plan.
Normally many weather incorporation methods can be used to satisfy the contract requirements. In order to claim time for unusually severe weather, it is common practice that the documented adverse weather days in excess of the monthly allowances must affect the completion of critical path activities. A good way to track and plan for weather days and planning for the activities they impact is a scheduling model that incorporates adverse weather days into a weather calendar. The weather calendar is tied to the weather sensitive activities.
This task typically involves: •Documentation of all activities in the schedule that are prone to adverse weather •Application of the weather calendar to activities subject to adverse weather •Development of a baseline schedule in accordance with the project scheduling specifications •Calculation of the new finish date (Sabol 2004) Type of Work The type of construction work greatly influences the impact weather has on a project. Certain activities are particularly sensitive to weather conditions; meanwhile other tasks are not as sensitive to weather.
Others factors such as equipment being used, materials being used, and the activity durations for each activity influence the activities sensitivity to wind, temperature, and precipitation. The projects weather sensitivity also depends on the phase of construction. For example the initial phase of building construction is usually more sensitive to weather than when the building has an exterior shell up. Consequently the allocation of anticipated monthly weather delay in contracts is not sufficient.
The scheduled activities and sequencing of activities should be known before the number of monthly weather delay days has been determined because the weather impact is strictly associated with the type of construction activities being performed. Lingering Days Severe weather can have impact on a construction project for many days after the actual severe weather has passed. These lingering days may extend past severe weather periods because of drying time for soils, and accumulated water on the site and before and after snowy conditions. These lingering days are also known as dry out or mud days.
Even when trying to specify the number of adverse weather days, a contract is still ambiguous if it does not determine how to deal with lingering days. It is important to differentiate between lingering days caused by predictable and unpredictable weather conditions. Contracts should clearly spell out whether lingering days are included in the monthly normal weather days. For example in Tennessee, adverse weather may include dry out or mud days at a rate of no greater than one make up day for each day or consecutive days beyond the standard baseline that total 1. inch or more of rain. (Syzdik 2012) Lost Days Adverse weather can greatly reduce productivity. Working under adverse weather conditions causes the jobsite efficiency to decrease even though the work might not stop. The decreased productivity due to adverse weather can contribute to schedule delay. The adverse weather not only delays a project due to such direct lost days from a weather event, or dry out days, it also prolongs schedule activities due to lost productivity or inefficiency. This in turn, can delay the overall project schedule.
In many circumstances, a contractor is not entitled to compensation incurred by lost labor productivity caused by unusually severe weather, usually only lost time that is associated with unusually adverse weather can be recovered. Personal Opinion If the contract does not specify what constitutes as normally severe weather and determines the weather thresholds for different work to be performed a consistent analysis of severe weather will be impossible. The contracts should specify monthly anticipated weather delay days.
Contractors should account for these days when planning their work and planning their baseline schedules. These delay days should include anticipated lingering days based on the construction activities scheduled in the periods of anticipated severe weather. My experience working on a farm has taught me that weather delays happen frequently and these delays throw a wrench in all of the plans. For example during custom harvesting, a rainstorm will bring a halt to all combine harvesting.
Often if it rains more that a few hundredths of an inch work is stopped for at least one full day. This becomes an issue when there is another customer waiting to have their crops harvested but we have to sit and wait in one location for the crops to dry out enough to be cut, before we can move to the next location. If the crops are not harvested soon there is a chance that the crops could be destroyed by a hailstorm, or the crop could lose value if it gets rained on because the coloring gets washed from the grains.
This has taught me that proper planning and scheduling can help to minimize the losses associated with severe weather delays. Conclusion Adverse weather conditions and delays in construction are a source of costly claims and disputes in construction. Contracts should include monthly anticipated weather delay days, and a system to define or determine anticipated lingering days should be clearly defined in the contract along with threshold values for weather parameters.
These weather threshold values play a critical role when determining if weather is unusually or usually severe. Finally contracts should address the requisites to request a time extension cause by inefficiency due to unusually severe weather conditions. Much of the litigation resulting from weather delay disputes is based on the lack of adequate terms in the contracts. Whether a day with adverse weather is workable or not depends on the weather thresholds. The bottom line is, plan as for normal adverse weather, and know what the contract requires for adverse weather.
Records should be kept of adverse weather occurrences, and time extension request should be submitted as required by the contract. When a project experiences adverse weather, the best case scenario is that weather considerations are included within the contract and in the schedule as applicable standards with respect to approach and evaluation. If weather impacts become an issue and are not present in the contract, the project management team and scheduler should develop reasonable weather allowance.
If it becomes necessary to implement a method mid project, it is very important that the weather allowance standards are acceptable to all the construction parties and that all the assumptions used in the risk analysis are consistent and accurate. Bibliography Glavinich, Thomas. Construction Planning and Scheduling. Edited by Second Edition. The Associated General Contractors of America. Long, Nguyen. Analysis of adverse weather for excusable delays. American Society of Civil Engineers. 5 26, 2010. ascelibrary. org/coo/resource/1/jcemd4/v136/i12/p1258_s1? iew=fulltext> (accessed 4 4, 2012). Morosko, Nick, interview by Andrew Barthel. Project Manager Bozeman, MT, (4 2, 2012). Sabol, Kevin. Integrated Framework for Quantifying and Predicting Weather related delays. American Society of Civil Engineers. 8 16, 2004. ascelibrary. org/coo/resources/1/jcemd4/v136 (accessed 4 6, 2012). Syzdik, Brian. Weather Considerations for Construction Project Scheduling Models. Society of American Military Engineers. 10 12, 2012. militaryengineers. wordpress. com/2010/10/12 (accessed 3 24, 2012).