The Netherlands is grappling with a substantial housing crisis, marked by an estimated shortage of 380,000 houses. To address this issue, an annual creation of 100,000 new housing units is deemed necessary. However, the current construction rate stands at only 70,000 houses per year, indicating a considerable gap in resolving the housing crisis. Recognizing the potential of urban densification, especially through vertical extension using Cross-Laminated Timber (CLT), presents a sustainable solution. Nevertheless, challenges arise, such as the unique approach to vertical extension and the structural constraints posed by CLT's lower strength compared to materials like concrete.

This research aims to identify the vertical extension potential of CLT in existing buildings by developing a parametric tool that considers various structural constraints. The ultimate goal is to contribute to informed decision-making practices for sustainable and effective structural design in vertical extensions.

The methodology comprises four phases: analysis, synthesis, simulation, and evaluation. The analysis phase examines existing vertical extensions, structural context, and spare capacity concepts, forming the basis for synthesis. A parametric tool is then created using Grasshopper and Karamba, employed in the simulation phase to conduct a parameter study based on the analysis phase findings. This study assesses the effects of the original structure's base geometry on spare capacity and evaluates the design of the extension itself.

The results of the parameter study reveal that the presence and placement of a stability core have the most significant impact on spare capacity in the existing building. The original construction grid and building height also influence spare capacity, though to a lesser extent. Additionally, wall layouts in the extension, such as core alignment, functional design, and façade-aligned layouts, significantly affect spare capacity utilization in both the original structure and the extension.

Variations in extension grid show differences in spare capacity utilization, with effects smaller in magnitude compared to wall layout variations and displaying less dependence on the original structure's geometry. In the vertical extension itself, failure tends to concentrate on connections between CLT panels and floors, particularly with wall layouts emphasizing functional design.

In conclusion, the research, coupled with the development of a parametric tool, successfully achieves its main goal. The tool's accuracy is validated through extensive assessments of horizontal load transfer from the extension to the original structure. The parameter study highlights the significant effects of various parameters on extension design and the original structure, emphasizing the tool's utility in exploratory design stages for vertical extensions.