The Royal Botanic Gardens in Sydney recently opened its newest horticultural display space, the Calyx, designed by PTW Architects and McGregor Coxall.

The circular structure is made from a series of radiating steel frames and is set beside Ken Woolley’s Arc glasshouse built in 1987.

According to Troy Uleman, Project Director of PTW Architects, designing a building for a flexible horticultural display set within a landscape of national historic importance, required an architectural approach that would not detract from the importance of its setting. PTW based its design on a ‘jewel in the Garden’ concept, creating a serene and peaceful building with the capacity to adapt to ever-changing requirements.

Built at the site of the Arc Greenhouse in the Garden, The Calyx applies intelligent and sensitive architecture to reinvent itself through emotive and informative exhibitions changing every six to nine months.

Working with Cockram Construction, the PTW team designed the highly flexible building using existing elements of the Arc, originally designed and constructed in 1994 by renowned Australian architect, Ken Woolley, while retaining the extraordinary design quality, integrity and innovation of the existing structure.

A circular steel structure, the Iris is the most visually engaging element of the building and is also the most highly visible segment of the building from afar. Containing the foyer, education and retail space, it can be turned into an event space at night with retractable walls that allow the exhibition and event spaces to be combined.


Client Group Project Team: Project Director - BGCP Director, Strategy and Projects; Project Sponsor - BGCP Director, Horticulture; Project Manager - Root Projects Australia; Quantity Surveyor - WT Partnership; Mechanical Peer Review - Flux

Design & Construct Project Team: Contractor - Cockram Construction; Architect - PTW Architects
Project Team: Troy Uleman, Neill Hill, Glenn Harper, Sara Best, Rod Brown, John Shipp and Rebecca Qin; Landscape Architect - McGregor Coxall; Services Engineers – Jacobs; Structural Engineer - BG&E; Heritage/Archaeology - GML Heritage; Planner – Urbis; Certifier – DLA; Arborist - Tree Wise Men; Access - Morris Goding Accessibility Consulting