It is rare for an outdoor project not to be affected by wet weather. If you manage an outdoor project, changes in your project schedule due to wet weather delays are something you will have to deal with. You must allow for this.
Problem: Wet weather schedule delays are difficult to get accepted
Wet weather can severely impact the delivery schedule (and associated costs) of a project that includes work outside or that is dependent on outdoor work. However, many clients are reluctant to extend schedules or approve extra costs due to wet weather delays.
Solution: Allow for wet weather in project schedules, and report on this
If you are the project manager on an outdoor project for delivery for a client, you should allow for wet weather in your schedule.
A study in the UK showed that UK project durations are extended for an average of 21% due to the weather.
Most clients will usually only allow variations (time or costs) for wet weather delays if those wet weather delays meet a certain criteria. That criteria is usually based on rainfall being recorded in that area (either by official sources or from an onsite rain gauge) for more than a set number of days for that month.
For example, a contract may officially state that you should allow for 5 days of wet weather in each month of the project (or a variation of that for each month), and that variations will only be granted for wet weather delays if the recorded rainfall is more than that number of days. If the contract does not state this, you should get the official local government average rain days for that area (such as this map from the Australian Bureau of Meteorology) and allow for that in your contract offer (and state the number of rain days allowed for each month).
By showing the number of wet weather days clearly in your schedule, you make it much easier to get extension of time or cost claims approved by your client. When wet weather does occur that influences your work schedule, you should make clear records of this, and communicate to the client that the weather may delay the schedule. If it does then affect the schedule, you should inform the client as soon as possible and also inform them that you will need to make an extension of time claim and possible cost claim as per the contract. You should also use a formal extension of time claim form, preferably your clients form, or, if they don’t have one, then using your own template, such as this template shown on Sitemate.
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In your monthly reports, you should also list the number of wet weather days allowed for, used, and remaining so that wet weather extensions are easy to apply for, based on the evidence you have already provided.
If you are the project manager on the client side, you should make the same allowances in your schedule, and you should ideally state the wet weather day allowances in your tender / offer request, and in the contract. A clearly written section on this in the contract makes the effects of rain clear to both parties.
Don’t forget the impacts that the wet weather will have on your project after the actual day of rain. The ground may be too wet for excavation work until it has dried out. Flooding may have moved materials or damaged equipment. Lightning or wind may have damaged or destroyed equipment, which will have cost and time impacts to replace.
You should put measures in place to mitigate these effects. Measures such as extra drainage, not having laydown areas at a low point, and having pumps ready to move water away from the site etc. Also don’t forget to schedule work for dry periods (not the rainy season). Paul Netscher has a great article on avoiding weather related project delays on his construction project management site.
If you have all these measures in place, have done adequate allowances in your schedule for the effects of weather, and have kept your client informed of the wet weather and your preparations, you should have sufficient reasons and evidence for your client to allow schedule delays without penalty to your project. But make sure your contract allows for this.
Lesson: Allow for and report on wet weather delays
Wet weather can cause project delays. You should allow for wet weather days, both in your proposals that you submit to clients (or to potential clients) and also if you are managing a project that requires work by construction companies (i.e. if your company is the client). Show this clearly in your schedule and report this regularly to your client, especially if you need to notify the client of delays. This will make extensions of time and cost easier.