ABOUT US
Holzraum System is a consulting and education partnership that combines decades of expertise in architectural, structural, and heavy timber design, with a focus on off-site manufactured, high-performance, low-carbon construction. Specializing in DFMA (Design for Manufacturing and Assembly) for wooden structures, we aim to bridge the gap between builders, architects, and off-site manufacturers, integrating Passive House principles and streamlined workflows. Our goal is to foster collaboration among project teams, ensuring projects are successful, efficient, and repeatable.
Ilka Cassidy, Dipl.-Ing. Architecture, CPHC, (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. Through Holzraum System, she has worked to merge the precision and scalability of prefabrication with the use of healthy, low-carbon materials, all while optimizing energy efficiency with Passive House principles. She has guided multiple single and multifamily projects through Phius certification.
Ilka is also committed to expanding knowledge in the industry, serving as co-host of the Passive House Accelerator Podcast and Construction Tech Live events. She is a frequent conference speaker and an active member of Green Building United in Philadelphia as well as NESEA.
Steve Hessler (co-founder) is a heavy timber structural designer, project manager and PHIUS+ certified passive house consultant with over 25 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.
A frequent industry speaker and contributor, his award-winning projects span passive houses, net-zero buildings, and large-scale timber structures. His work continues to drive innovation in digital prefabrication and high-performance construction.
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