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 2000.

Jan Karel has served as a president and member of numerous Boards of professional, educational and sports organisations and advisory committees such as the Dutch Association of Environmental Professionals (VVM), the European Network of Environmental Professionals (ENEP, Brussels, which he cofounded and led for 10 years), the Open University in the Netherlands, the University of Antwerp (Belgium) and the Royal Dutch Rowing Federation. He is currently the president of the Wageningen University Fund and an advisory Board member of several firms.


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.



Olivier Severini
Member of the Group Executive Board
Managing Director of Deerns France and Italy

Olivier Severini is an engineering graduate from l’Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques Sciences (ENSIACET) in Toulouse. After his graduation, he expanded his knowledge in the area of management with an MBA at l’école des Hautes Etudes Commerciales (HEC Paris).

Olivier started his career as a Change Management Consultant specializing in industrial restructurations for international renowned firms mainly in the food and in the aerospace industry. After 5 years, he joined Altran, one of the leader in innovation and high-tech engineering consulting to lead the aerospace business unit in Toulouse. He rapidly evolved towards a corporate role within the M&A team, leading the post-acquisition process for the companies newly acquired. Olivier operated mainly in Italy, Spain, Switzerland and finally in the UK where he became familiar with the Building Services Industry.

When he joined Deerns on November 2010, Olivier created Deerns France office in Paris that has now established a solid reputation of the Group on the French market. Olivier was also instrumental in the acquisition of Deerns Italia in March 2012, of which he took the responsibility from day one. He also led the opening of Deerns in São Paulo (Brazil) on February 2014. Since 1 January 2012, Olivier is member of the Group Executive Board.

Olivier is giving regular lectures at HEC on matters related to business development, international business or managing firms recently acquired. He is also mentoring young graduated or experienced alumni from his business school. In a recent past, he acted as a special advisor for AFEX (Association supporting French Architects for their business diversification abroad).



Erik Lousberg (1964)
Member of the Group Executive Board
Chairman of the Executive Board Deerns Nederland

Erik Lousberg is an engineering graduate from the Zuyd University of Applied Sciences in Heerlen. After his graduation, he expanded his knowledge in the areas of energy supply and mechanical engineering, project management, and corporate management. In 2005, he completed his Executive MBA studies at the Rotterdam School of Management, Erasmus University.

Since 1 January 2012, Erik has been chairman of the executive board of Deerns Nederland B.V. Erik Lousberg entered into employment with Deerns in June of 2000, as Manager Business Development. In 2001, he was put in charge of the Eindhoven subsidiary. In 2008, he became a member of the Executive Board. Before Erik was appointed by Deerns, he had been working for an engineering consultancy in Nijmegen for ten years, occupying a number of positions.

Erik Lousberg is a member of the Supervisory Board of ISSO, knowledge institute for the engineering sector. In the past, he has been active in the executive committees of various associations, including TVVL, NVTG, DIO and NIRIA. Within the context of education for the engineering sector, he has long been involved in various post-bachelor’s and master’s training courses with Avans+, for example as chairman of the education advisory board OpleidingsAdviesRaad. He also helped initiate and set up the MIT-E training courses in the Netherlands, and the training course MEP design for civil engineers.