Construction Project Management
Planning & Scheduling
Bar Charts
Building a CPM Schedule
Networks & Logic
CPM Scheduling
Logic Relationships & Precedence Networks
Progress Updating

Step 2 – Estimating Durations

When you estimate the duration of an activity, many factors are involved. But productivity is the most important factor.

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All right, so we broken down the construction project into activities. And now in step two, we need to find the durations, or estimate the durations, of each one of them. This is a very important step because this step will actually determine or impact the calculations of the critical path method.

First of all, as we said before, we have to pick a unit of time for the project. For all the activities in the project. And I've seen most construction projects use the day unit. Although sometimes in crunch time we may schedule by the hour. And if the project is huge and this is a summary project we may use the week. But let's talk about days. For example, here if the nature of that activity lends itself to this simple method then it's great if that productivity of the project is linear throughout the duration of the activity.

For example, here we have excavation. Let's say this is excavation of a foundation of a building. And we estimate that our crew can do 800 cubic meters or cubic yards per day. And the total quantity is 10,000 cubic meters. So what we do is divide the total quantity by the crew production per day. That's 10,000 cubic meters divided by 800.

And the answer is 12 and a half days. We don't like to put 12 and a half days so we rounded up to 13 days and we think of that half day as a little bit of a buffer or a time contingency. We need...

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