What is a Hammock Activity?
Hammocks… is the first thing that comes to mind a beautiful sandy beach, dotted with palm trees and fabric slung between them? Or perhaps you picture a forest setting, with your bed for the night hung between two majestic tree trunks?
If you are a project professional, you’re likely to think of something else first: that helpful summary task that links multiple unconnected activities and helps track hard-to-measure things like management effort.
No? You don’t picture a network diagram when we talk about hammocks? Let’s change that! In this article you’ll learn everything you need to know about this valuable addition to the way you schedule work on projects.
What is a hammock activity and when it is used?
A hammock activity in scheduling is an activity that spans two points in a project schedule. It ‘hangs’ between those two points and is often shown on activity-on-arrow diagrams underneath those two points. We guess the name has come about as on the schedule it looks a little like a hammock hanging between a couple of trees.
Hammock tasks are used when it is valuable to link activities and show associated costs, codes, resources, resource calendars, descriptions notes and so on – all the normal attributes you’d find in your scheduling tools that associate with a planned activity.
While you might not use an activity-on-arrow diagram or network diagrams much in your daily project management, you can still set up hammocks in your scheduling tools. However, be aware that it’s an older project scheduling term, and you may find your software confusingly labels similar tasks as level of effort activities.
Hammock activity duration
A hammock activity has no fixed duration. The time assigned to the activity is flexible and is driven by logic from the rest of the schedule. When the duration of other scheduled tasks changes, the hammock is updated automatically to reflect the changes. It reflects the overall duration of the individual activity.
The duration of the hammock is calculated from the start date of the earliest task in it, and the finish date of the task that finishes last. The order of the tasks might not matter, and they could switch around as the work progresses.
Purpose of a hammock activity
The purpose of a hammock activity is to carry overhead costs and resources during a portion of the project. Like a level of effort task, it’s a way to apportion overheads without having to split them between the other activities or to summarize time required as a result of several tasks. The project manager’s time is one item that might be appropriate to apportion in this way, if the effort cannot be adequately accounted for in another way.
Another benefit for project managers and schedulers is that the tasks within the group do not need to be related to each other. Dissimilar work can be ‘hung’ together and grouped in a way that makes sense for management effort.
Hammock activities can also be used to create summary reports. However, one of the advantages of using hammocks over ‘standard’ summary tasks is that they can summarize activities across multiple areas of the project schedule, not just tasks in a single section.
Hammock activity examples
As a summary activity in project management, these tasks do not have a fixed duration. The duration is derived from linked activities, so think about that as you consider examples in your own projects.
Here are a few examples:
- A collection of milestones that are used for project reporting
- A group of items that provide a management summary e.g. content that would be reported in time-phased reports for the quarter
- Ongoing activities that span the length of the project or sub-component of the project e.g. project management effort, invoicing, supplier liaison.
The easiest way to see how these tasks work is to set one up in your scheduling tool. We have a guide to using hammock tasks in Microsoft Project that will help.
There are differences between Project and Primavera in how they treat this kind of activity, so make sure you train schedulers on how best to address adding administrative tasks like the risk management effort. (Need some help with that? We offer an on-demand scheduling best practice training).
Hammock activities in construction
Hammock tasks in construction are useful for determining duration of events like how long equipment will be required on site. They can carry the associated overhead resources and appropriate costs.
The hierarchical sense of the work breakdown structure does not need to apply, and there’s no need to stick to an individual sequence of events. Different types of activity like equipment use, concreting, erecting scaffolding, interior work and more can be put together.
It’s worth learning how to use this feature in your project management software, because it offers a valuable way of separating out resource assignments for overheads and the cost of project management. It’s also a smart way to schedule when you use earned value management techniques and can be useful for management reports.
Project scheduling can be difficult if you are just building competence in the tools you have. Why not outsource project scheduling and let us do the heavy lifting for you?