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Holzraum System is a design and consulting partnership combining decades of experience in architectural, structural and heavy timber design, high performance and Passive House construction, CADCAM (computer aided manufacturing) for wooden structures and software development for streamlining design and manufacturing processes. Formed as a Passive House consulting and building envelope design to manufacturing firm, Holzraum System was based on our commitment to connecting builders and architects with passive house and off-site manufacturing in order to achieve unmatched comfort, superb air quality, extreme building resiliency, and among the lowest embodied  + operational carbon footprints in the building envelope industry.

Ilka Cassidy (co-founder) is passionate about Passive House envelope design and building science, focusing on the benefits of natural building materials. She grew up in Germany and received her Diploma of Engineering/ Architecture degree from the RWTH Aachen. Ilka connected to the US during her year at the University of Washington in Seattle where she won a Scholarship to study within the graduate program. Eventually she moved to Philadelphia where she co-founded C2 Architecture in 2005. She has worked on multiple projects as a Certified Passive House Consultant and is an active member of Green Building United in Philadelphia.


Steve Hessler (co-founder) is a heavy timber structural designer, project manager and PHIUS+ certified passive house consultant with over 20 years of experience designing, building and managing structural-thermal envelope offsite fabrication projects as well as on-site high performance construction projects.  Since 2008 Steve has been combining 3D modeling, integrated project delivery and building science principals to design and manage off-the-grid, net-zero, and passive house projects. Steve received his bachelors in Communications Strategies from the Pennsylvania State University in 1990 before completing a five year apprenticeship program as journeyman and lead restoration carpenter.

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David Hessler (co-founder) is a biologist, computer programmer, and entrepreneur who has worked in biopharm development, and co-founded three startups: a biotechnology company and two scientific software development companies. He has served as a senior software director and product portfolio manager for BIOVIA Dassault Systemes, and served on the project management team for construction of 30 custom homes in Ecovillage @ Ithaca, NY. David received a Biology degree from the Pennsylvania State University, and did graduate work in biochemistry at the University of Rochester.


Emily Dodson (designer) (Assoc. AIA, LEED GA, CPHC in training) works towards the marriage of building science with efficient design and construction, believing very much that architects have a responsibility to advocate for human health and high performance.  She has experience at both large and small architecture firms in Philadelphia, where she collaborated in the design of cultural and educational institution projects, pro-bono community outreach projects, and multi-family residential projects.  She has enjoyed opportunities to implement energy modeling and environmental research into designing for new construction.  Emily holds a Bachelor of Science in Architecture from Temple University and a Master of Architecture from the University of Pennsylvania, with certificates in Sustainability and Ecological Architecture.

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Matt Bischoff (software developer) is the lead developer of Holzraum Catch and has over 10 years of experience in developing web applications. He has a strong background in full stack development, and has a solid understanding of software architecture, design patterns and database management. Matt is a skilled problem solver who enjoys writing software to solve real-world problems. Matt received his bachelor's degree in Computer Science from Ithaca College in 2012. 


Sydney Hibshman (structural designer) graduated in 2015 and started working in high-end custom metal, glass, and wood fabrication. In short order they were consumed by actualizing projects from conception through design and fabrication to installation. They have worked on projects like the facade of Zaha Hadid’s 520 W. 28th street Highline residential project and Santiago Calatrava’s World Trade Center ‘Oculus’ train station. They are thrilled to be bringing the skills learned in their early career to Holzraum and see projects realized with sustainability and building performance as driving principals. Syd holds a Bachelor’s degree in architecture from Temple University’s Tyler School of Art. 

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