Planning for permeability delivers measurable benefits to the community, environment, and economy — up to $2.20 for every dollar invested.
The City of Port Phillip engaged SGS Economics & Planning to assess options for outcomes-based planning requirements that improve permeability across residential and commercial developments. Current planning controls specify a 20% pervious surface requirement for residential uses. This study examined how equivalent environmental outcomes can be achieved through alternative design solutions, such as green roofs, rainwater tanks, and permeable paving.
Working with Hansen Partnership, who modelled feasible design solutions for five building types, SGS conducted a cost benefit analysis to test the economic and social value of introducing permeability equivalence requirements. Using SGS’s Small Area Land Use (SAM) model, we projected the uptake of new buildings over time and modelled how local and neighbourhood-level benefits—such as urban cooling, energy savings, reduced emissions, and improved health outcomes—emerge as green cover increases.
The results showed that for every dollar invested, permeability alternatives deliver between $1.80 and $2.20 in community, economic, and environmental benefits. The findings demonstrate that integrating permeability equivalence into planning controls is both feasible and beneficial, providing a strong evidence base for policy reform.
This is the first known study in Australia to apply economic evaluation techniques to permeability in planning. It offers a replicable framework that combines economics, land use modelling, and design expertise to support data-driven decisions and advance more resilient, sustainable urban environments.
This project was nominated for planning excellence at the 2025 PIA VIC Awards.
