Construction Project Management
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Building a CPM Schedule
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Proper Use of Lag & Lead Time

[Whiteboard session] Lag and lead time is often misused in schedules. Find out how to best use lag and lead time on your schedule, the right way.

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What are these lags used for waiting periods when there is time passing? However, there are no resources, no real work, no money. An example is concrete curing when we put a concrete slab or column or sheer wall and we're waiting two, three days for the company to dehydrate. And then we come and strip the form work. Also when we are waiting for a permit to be issued, asphalt to be cured also and many activities that have to wait. Now the common mistake that some people fall into, they don't want to use lags.

Instead, they have that period of time built-in with the duration. And that's wrong. Let me give you an example. You go and apply for a permit and they tell you it needs 90 days. Some people would have a 90-day duration activity called obtaining a permit, I wouldn't do that. I would have one day applying for a permit, and then a lag of 90 days or 89 days, whatever it is, and then a milestone or an event saying permit issued.

Why do we do this? Because in some instances, the computer program calculates the percent complete of the project. And one of the methods, there are many methods, one of the methods it takes into consideration the weight of the activity and that weight is proportional to its duration. So when you put 90-day duration, you give that activity, humongous weight, a lot more than let's say, pouring concrete for a suspended slab.

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