Efforts to quantify and reduce greenhouse gas (GHG) emissions of the built environment often neglect embodied emissions, instead focusing on reducing emissions from building operations. Sustainably sourced mass timber buildings offer a low embodied carbon alternative to traditional concrete and steel structural systems, however the variability in embodied carbon for different mass timber structural systems remains understudied. In this study, we used life cycle assessment (LCA) to compare the whole-building embodied carbon of nine mass timber design options for an eight-story mixed-use building, ensuring structural, acoustic, thermal, programmatic, and fire-rating equivalence between the designs. The study found that the mass timber designs vary significantly, ranging between a 14-52% reduction in whole building embodied carbon from the baseline concrete and steel cases, and a 31-73% reduction when considering the structural system alone. This study demonstrates the value that whole building LCA (WBLCA) provides as a primary driver for structural system design and architectural development of mass timber buildings, rather than single material comparisons using environmental product declarations (EPDs).