Group Executive Board

Jan Karel Mak (1957)
CEO Deerns Group  

After completing his graduate studies in Environmental Sciences at Wageningen University and the Harvard School of Public Health, Jan Karel Mak worked for seven years as a consulting engineer, project manager and business leader at DHV consulting engineers. He then spent four years as a management consultant at McKinsey & Company, followed by four years as managing director of Arcadis’ Dutch consulting engineering arm (‘Heidemij Advies’ at the time).

He joined Deerns Group as a managing director in 1999, shortly thereafter became a shareholder, and has been serving as Chief Executive Officer since 2001.

Jan Karel serves various charitable organisations: he is the president of the Board of Wageningen University Fund and of the European Supervisory Board of Solidaridad, and is an advisor to GreenfieldCities. He is also an advisory Board member of several Dutch technology firms (e.g. Innovatic, VideoWindows).

He has served as a president and member of numerous other Boards of professional, educational and sports organisations, e.g. the Dutch Association of Environmental Professionals (VVM), the Dutch sustainable employers federation ‘De Groene Zaak’, and the Royal Dutch Rowing Federation (KNRB).



Roel Rooskens
CFO Deerns Group

Roel Rooskens is CFO of the Deerns Group and member of the Group Executive Board since January 2012. Prior to joining Deerns in 2011, Roel has worked in various financial roles within the Telecom and IT industry and lastly as a Group Controller for the Insulation & Rooflights division of a large building materials company, CRH.

He holds a degree in Economics from Tilburg University, The Netherlands. In 2004 Roel completed the RC Post Master Controllers Programme at the Nyenrode University, The Netherlands.


Tjerk van der Meer (1974)
Member Group Executive Board
Deerns Group

Tjerk van der Meer is member of the Group Executive Board Deerns Group since June 2019.

Before joining Deerns, Tjerk was globally responsible for commerce and strategy in the Manufacturing & Technology sectors at Arcadis. Prior to that he occupied various international management positions at, among others, design and engineering firm Royal HaskoningDHV.