Journal of Construction in Developing Countries, 25(1), 129–146, 2020 © Penerbit Universiti Sains Malaysia, 2020. This work is licensed under the terms of the Creative Commons Attribution (CC BY) (http://creativecommons.org/licenses/by/4.0/). Time and Cost Overruns on Large Projects: Understanding the Root Cause * Sitwala Simushi 1 and Jan Wium 2 Published online: 15 July 2020 To cite this article: Sitwala Simushi and Jan Wium (2020). Time and cost overruns on large projects: Understanding the root cause. Journal of Construction in Developing Countries, 25(1): 129–146. https://doi.org/10.21315/jcdc2020.25.1.7. To link to this article: https://doi.org/10.21315/jcdc2020.25.1.7 Abstract: Time and cost overruns are a persistent problem on large projects despite apparent progress of the project management profession. This article reports on fndings from research carried out on large projects in South Africa to fnd the root cause of this phenomenon. The article begins by investigating the existing theories on the causes of time and cost overruns followed by empirical investigation using case studies. The results showed that time and cost overruns on large projects originated from the external environment which in turn affected the organisation and the project environments. The root cause was found to be a lack of project-specifc experience by the project team, external and organisational decisions in the past, community resistance and pressure on the project team and scope change drive from stakeholders. From the results, it is proposed that an effective strategy to reduce time and cost overruns should involve not only the management of the project environment but also the organisation and external environments. The article adds knowledge to the overrun causation theory and management of large projects. Keywords: Overruns, Root cause, Large projects, South Africa, Overrun causation theory INTRODUCTION The recurrent problem of time and cost overruns on large projects has been noted by many scholars over the years (Dahl et al., 2017; Merrow, 2011; Morris and Hough, 1987; Mukuka, Aigbavboa and Thwala, 2015; Senouci, Ismail and Eldin, 2016). Most scholars have attempted to understand this phenomenon by investigating singular, independent causes or most signifcant factors that lead to time and cost overruns. Few have attempted to understand in-depth, how time and cost overruns develop in large projects (Love et al., 2014), or the interaction of the various variables leading to time and cost overruns as noted by Ahiaga-Dagbui et al. (2015). There is, therefore, an incomplete theory and understanding of the phenomenon of time and cost overruns (Love, Ahiaga-Dagbui and Irani, 2016) as conventional research has tended to use research methods which are ill-suited for an in-depth understanding of the actuality of managing projects (AlSehaimi, Koskela and Tzortzopoulos, 2013). The methods are dependent on the general opinions of the practitioners, unlike project-specifc and contextual reality of projects, thus making them superfcial, simplistic and mostly replicative as noted by Ahiaga-Dagbui et al. (2015). This has, in turn, affected the approach to project management strategies and solutions proposed. 1 School of Built Environment, Copperbelt University, ZAMBIA 2 Faculty of Engineering, Stellenbosch University, SOUTH AFRICA *Corresponding author: simushis@yahoo.com