As founding principal, Lehmann provides overall vision and project leadership for his studio — while maintaining an active role as one of the field's leading advocates for sustainable design.
He has spent decades advancing urban transformation through design principles that directly address climate change. His work consistently promotes the compact, mixed-use, walkable city as the optimal model of urbanisation — integrating innovative low-carbon technologies, green infrastructure, and sustainable consumption to meet the pressures of rapid urban growth.
Central to his approach are adaptive reuse and circular economy principles: retrofitting existing urban structures to preserve embodied energy, eliminate waste, and close the loop on urban metabolisms. His position is direct — "the most sustainable building is always the one that already exists" — a conviction that prioritises the regeneration of existing districts over demolition, and resource efficiency over resource consumption. The argument is developed at length in his 2010 book, The Principles of Green Urbanism, and 2019 book, Urban Regeneration. A Manifesto.
Sustainable Design and Beyond
As inaugural director of the Zero Waste SA Research Centre for Sustainable Design and Behaviour at the University of South Australia, he developed with A. Zaman the Zero Waste Lifecycle Index — embedding the waste hierarchy (avoidance, reuse, recycling, and recovery) directly into urban design and construction practice. This field-defining framework incorporates design for disassembly and extended producer responsibility, and is oriented towards behavioural change: engaging stakeholders, reducing consumption, and integrating resource recovery into the rhythms of everyday urban life.
The Principles of Green Urbanism (2010) remains his landmark theoretical contribution — a holistic strategic framework for transforming cities, incorporating behavioural incentives and low-carbon innovation designed to decouple economic growth from material consumption.
His work has shaped global policy and standards in urban sustainability, most notably through contributions to UN-Habitat. His 2016 Global Urban Lecture, "Transforming the City towards Low-Carbon Resilience," informed the New Urban Agenda by advocating integrated approaches to growth boundaries and green infrastructure. His research on zero-waste optimisation — referenced in UN-Habitat reports — has further influenced resource-efficiency guidelines for cities in the developing world, promoting scalable circular models and material reuse.
