Architect: Cracknell + Lonergan
Builder: Peter Lucas
Location: Dolans Bay, NSW
The Lyons House in Dolans Bay, a State Heritage-listed residence designed by the influential architect Robin Boyd, represents a bold exploration of form and structural balance. Constructed around 1967, the two-storey building is characterised by a first floor that cantilevers approximately 3.5 metres beyond the ground floor facade on all four sides.
This design centres around an elevated external terrace and swimming pool, creating a private outdoor sanctuary enclosed by the upper-level living areas. Partridge was engaged to conduct a structural condition assessment following reports of perceptible building movement during high wind events.
The ground floor utilises a traditional concrete slab and load-bearing masonry wall construction, providing a solid base for the lightweight timber-framed first floor. The significant cantilevers are managed through a system of timber beams and diagonal timber struts braced against the ground floor structure. To achieve the double cantilevers at each corner, hybrid steel and timber trusses are concealed within the first floor facades on the southeast and northwest elevations.
Using Spacegass, our team developed a comprehensive structural model to analyse the building’s response to dead, imposed, and wind loads. This technical review identified potential wind uplift issues at the furthest points of the double cantilevers. The analysis confirmed that the eastern corner, which faces the highest wind exposure, experienced the most significant uplift forces.
Collaborating with the heritage architects at Cracknell + Lonergan, we designed a strengthening scheme to improve occupant comfort and structural resilience. This involved integrating a steel beam within the first floor framing in the eastern corner to reinforce the existing hybrid truss and bring wind uplift deflections within tolerable limits. We also developed rectification details to securely tie the base of the diagonal timber struts to the ground floor structure. These measures ensure the house can resist wind uplift forces during extreme weather events, protecting the heritage fabric from potential damage under ultimate limit state loading.
