In january 2009 he founded 'one fine day': office for architectural design with the aim to complement his research as professor for digital design at the Fachhochschule Trier with a studio that focuses on the practical application of advanced digital design tech­niques and manufacturing processes. Prior to this Holger worked with UN Studio, Amsterdam, from 2002 until 2008 where he became senior architect in 2007. He collaborat­ed with UN Studio/United Architects, New York, on the competition entry for the World Trade Center site in 2002, and with Bolles+Wilson, Münster, on several projects and competitions in 2000/2001.