A Guide to the Construction Critical Path Method
Most construction projects are precise sequences of actions that must be done in order. You can’t build the second floor of a building before you’ve built the first. You can’t bring your interior decorators in until the walls have been built and the plaster has dried. Smaller projects may allow for ad hoc planning. But for bigger projects that involve several contractors and subcontractors, better construction project management is essential. That’s the promise of the Critical Path Method or CPM for short.
What CPM Is All About
The basics of CPM are simplification and common sense, both important factors when construction projects become complex. Start with the following:
- A list of all the different activities required in the construction project (the ‘Work Breakdown Structure’). Make the list vertical, running down the left-hand side of your page or screen.
- For each activity, the time needed to complete that activity. Use a timescale running from left to right, so that you can show the time required as a horizontal bar of the appropriate length.
- Dependencies between activities. For instance, painting and decorating needing to come after plastering has been done (and has dried properly.)
Now you can make a simple CPM chart. If one task must be done after another task, its horizontal bar gets plotted on your chart after the bar for the other task, i.e. further out in time and further out to the right of the chart. If there are tasks that can be done in parallel, their horizontal bars will be stacked, one above the other.
The Power of a Plan, Multiplied by Software
Software applications for construction project management can help you to manage it all. They also make it easier to change your project plan. That’s already a big plus compared to pencil and paper solutions. Apps for the critical path method can also help you determine:
- The shortest overall time in which your building work can be done. If a task or dependency is changed, the app instantly recalculates the end date.
- The leeway you have in the start and finish dates of each activity. If the electrician is running a day later than scheduled, it may not be a problem if other craftsmen need a week to fit all the window frames.
- The critical activities that determine the total time and possibilities for compressing the total time. You can easily experiment by reducing the number of such critical activities, by getting tasks done in parallel instead of sequentially, or by adding resources to a given task to do it faster.
Sharing the Knowledge and the Criticality
CPM is widely used in the construction industry. Show a construction manager for a large project a CPM chart, and he or she is likely to immediately recognize what it is. That gives you a common language and also a common base from which to work. Project planning can be shared with contractors and subcontractors. Cloud computing apps can make this particularly easy because they let you invite your building partners into the app online to see what must be done when. Mobile versions of these apps can be even more useful. You, your employees, and your partners can pull out a smartphone on the construction site to check progress at any time.
The Magic of CPM?
It can almost be considered an act of magic — but not quite. CPM still needs good quality input. On its own, it won’t know if you forgot about an activity. Neither will it know if it is reasonable to reduce timescales by adding more resources. For example, if the work of one plasterer takes six days to dry properly, putting two plasterers on the same job won’t make it dry in three days. So don’t automatically consider a CPM chart to be the ultimate truth. Know how it was made and any assumptions that went into it. Then let a good CPM software app help you stop biting your nails, track activities, prevent scheduling problems before they happen, and overall get your construction projects done on time.