The Origins of Hammocks and Ladders


By Patrick Weaver

Melbourne, Australia

Hammock and Ladders are activity types that were developed in the period 1961 to 1965. This paper is focused on outlining the development of these useful scheduling assets. However, it’s important to note Hammocks, LOE and Summary Activities are three completely different types of activity.

  • Summary Activities are a function of the coding structure in a schedule; at this time the origin of summary activities is uncertain, but the concept seems to have emerged in the mid-1980s as part of the move from DOS and text based scheduling tools to software designed to operate with the early Windows graphical user interface. The origins may be earlier (any advice on this will be welcome).
  • Level of Effort (LOE) activities are aligned with Level of Effort work packages in the WBS and Earned Value systems. Earned Value emerged in the 1970s.
  • Hammock activities are described in detail below.

All three activity types can be used to carry resources for a period of time (usually ‘overheads’ or supporting resources) and both Summary Activities and Hammocks can be used to create summary reports, but the differences in the way these three activity types are created and used is significant.

Hammock Activities

Hammocks are a cross between a link and an activity. A Hammock is an activity that spans between two points in a schedule. Having no set duration of its own, its duration is derived from the difference in time between the two ‘connection points’ in the schedule. It can be thought of as ‘hanging’ between these two points in the same way a normal hammock may hang between two trees.


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About the Author

patrick weaverPatrick Weaverflag-australia        

Melbourne, Australia

Patrick Weaver, PMP, PMI-SP, FAICD, FCIOB, is the Managing Director of Mosaic Project Services Pty Ltd, an Australian project management consultancy specialising in project control systems and a PMI Registered Education Provider. Patrick is also the business manager of Stakeholder Management Pty Ltd. He is a Fellow of the Chartered Institute of Building, Australasia (FCIOB) and a Fellow of the Australian Institute of Company Directors (FAICD). He is a member of the PMI College of Scheduling, and the PMI Melbourne Chapter (Australia), as well a full member of AIPM, APM (UK) and the College of Performance Management. Patrick has over 35 years experience in Project Management. His career was initially focused on the planning and managing of construction, engineering and infrastructure projects in the UK and Australia. The last 25 years has seen his businesses and experience expand to include the successful delivery of project scheduling services and PMOs in a range of government, ICT and business environments; with a strong focus on project management training. His consultancy work encompasses: developing and advising on project schedules, developing and presenting PM training courses, managing the development of internal project control systems for client organisations, and assisting with dispute resolution and claims management. He is a qualified Arbitrator. In the last few years, Patrick has sought to ‘give back’ to the industry he has participated in since leaving college through contributions to the development of the project management profession. In addition to his committee roles he has presented papers at a wide range of project management conferences in the USA, Europe, Asia and Australia, has an on-going role with the PMOZ conference in Australia and is part of the Australian delegation to ISO TC258. Patrick can be contacted at [email protected] or at www.mosaicprojects.com.au.

To see other works published in the PM World Journal by Patrick Weaver, visit his author showcase at http://pmworldlibrary.net/authors/patrick-weaver/