'Blue–Green' housing: designing for sustainable cities

The development of new housing in Australia is having a major impact on the ecosystems, including water systems, of our cities. There are models of housing, however, that can harmonise with the environment. We call this ‘blue–green’ housing.

These poor impacts are most clearly visible in the housing sprawl at the outskirts of our cities. Impacts are also occurring through poor infill housing within the middle suburbs. When we hear of the rise of ‘urban heat islands’ and the declining ‘urban forest’ in Australia, poor infill development is often the cause. Gradually, many of our spacious and leafy suburbs have been filled as housing has multiplied. In the process, suburbs have been built-out and paved over. They have lost backyards and front yards, along with vast numbers of trees. Residential densities have increased, but open space, shade, landscape and amenity have been sacrificed.

There is a demonstrated need to live more densely and to limit sprawl. This need must be supported by housing models that are well designed, sustainable and environmentally responsible.

Coordinated and well-designed infill housing offers a great opportunity to strengthen ‘blue–green’ systems in Australian cities, including our bushland, parks, recreation areas, tree canopy, verges, rivers, waterways and urban drainage networks. These have been called our ‘blue–green infrastructure’ – as vital to our health, safety and quality of life as all our other urban infrastructure.

Considered and designed appropriately, our cities and our housing developments can support more people, along with more flora, fauna, water, shade, recreation and amenity.

These challenges and opportunities have been a core focus of a research project undertaken by the CRC for Water Sensitive Cities a multidisciplinary research network established in 2012 to inform new approaches to urban water management in Australia. This network aims to foster cities that are well designed, cooler, greener, and as a result, more liveable for human inhabitants and more supportive of flora and fauna.

The CRC for Water Sensitive Cities project on infill housing brought together a range of practitioners and researchers to demonstrate blue–green housing. Drawing together expertise from architecture, urban design, climate modelling and water engineering industries, along with industry, government and community partnerships across Perth, Adelaide, Melbourne and Brisbane, the project crosses a range of scales and disciplines to demonstrate how a water sensitive city can support higher density communities while, at the same time, enhancing environmental values [1].

Delivering 'blue-green' infill housing

The project has involved strategic thinking, design and evaluation across a range of scales: from the single dwelling unit and housing type to the grouped site, extending to the precinct, all the way to the blue–green systems of the city. In many ways, poor infill outcomes are problems of scale. Lot-by-lot thinking is one of the central challenges in ‘business as usual’ infill housing — a lack of strategic planning and policy coordination that has come at the expense of good design and environmental outcomes.

Many of these impacts are gradual, happening cumulatively over many years. Such as the decrease in ground permeability (which impacts, among other things, the potential for rain to recharge aquifers), or the loss of tree canopy. On a single site the impact is small, but it becomes dramatic over time at a system scale. In Perth, in the decade between 2009 and 2018, tree canopy loss on private lots across inner-city suburbs was 644 hectares [2].

Addressing these issues requires new collaboration and coordination between design, science, planning and community. A key output of the project has been an evidence-based design guide in the form of a Typologies Catalogue.

This is an illustrated toolkit of infill units, arrangements and precincts, informed by principles that emerged from design research and quantitative testing. The range of models was iteratively developed in response to the feedback from hydrological and thermal calculations, including measurements for water sensitivity and urban thermal comfort, which demonstrate the benefits of the designs in scientific terms.

The infill typologies are underpinned by design approaches that achieve high-amenity dwellings, with careful regard to delivering open space. Critically, the designs have also been developed across different scales: starting with the dwelling units and typologies, to their arrangement on sites, working up to precincts, and their impacts upon city-scale systems.

Developing a range of suitable typologies

The availability of a range of dwelling types is important in ensuring environmentally responsive models of infill which can be easily replicated across cities. In the current context, there is a low range of medium-density housing types available on the market, a so called ‘missing middle’ in Australia [3].

By examining a range of typologies, the catalogue becomes useful across a range of contexts, from smaller scale infill of 30 dwellings per hectare, to medium and larger scale infill developments of 50 dwellings per hectare and higher. The designs include the courtyard, terrace, townhouse, stacked and cluster dwelling types and ’walk up’ and mid-rise apartment typologies. Many of these typologies were developed by the project design team while others were selected from national and international case studies for their applicability in Australian suburban settings.

The comparative benefits of 'blue-green' housing

At the site scale three scenarios were tested for each typology - a typical existing suburban condition of detached housing, standard 'business as usual' industry practice for infill development and a water sensitive design response. The advantages of the water sensitive scenario were demonstrated across dozens of parameters, among them canopy tree cover, deep root zones, ground permeability, occupancy, water consumption, urban heat and open space metrics.

In the study of the courtyard typology, for example, the water sensitive infill design increases existing tree canopy to more than 10 trees, nearly triples occupancy with up to 30 residents, and achieves 77% site permeability. On the same site, the ‘business as usual’ infill development allowed for only 2 canopy trees (removing 4 trees), up to 20 occupants and achieved only 21% permeability. The existing condition in this case was detached housing with large backyards: 6 canopy trees, up to 12 occupants and 59% permeability [4]. An ongoing process of design and redesign, quantification and re-quantification refined each of these designs based on a framework for architectural, urban space, thermal and water considerations.

The spatial arrangement of infill typologies on sites is a critical part of this design exercise. The housing arrangements proposed in the catalogue are best-practice designs with high amenity. They are optimised to channel northern light and prevailing breezes, with efficient and flexible internal planning, and generous connections to the outdoors. These are fundamental principles of good design that are lost in the 'business as usual' practice of infill housing owing to a range of factors that prioritise ‘yield’ above design: maximising the number of dwellings on each site, the number of rooms in each dwelling and number of carparks, and squeezing out open space.

Principles of good design are lost because of a low engagement of design expertise in housing, and because planning requirements have been slow to incorporate principles of good design. Open space in particular is rarely done well in 'business as usual' infill – becoming the unconsidered ‘left-over’ space between the dwelling and its boundaries. Well-designed open space became a key principle in the project because of its importance to both environmental performance and design amenity. A prioritisation of open space can ensure water sensitivity, the retention of trees and lowering of urban heat. Quantity, usability and connectivity of open space are all essential in well-designed infill housing.

The project’s principles address three realms of open space: private, communal and public spaces. Allowing for generous and connected open space within these three realms became a key design objective, a concept that is as important for humans as it is for ecosystems.

The incorporation of a useable, secure and private ‘outdoor room’ connected to the living spaces brings potential for recreation, sun and ventilation into the home. Beyond this, there is careful allocation of communal open space for shared amenity between residents, balancing connection and privacy for the dwellings. Areas with existing trees can become integral communal spaces, incorporating shared facilities. Driveways can be designed to have multiple functions, at times they might transform into communal spaces. With future flexibility in mind, driveways might change function altogether to become additional courtyards or gardens, particularly as modes of transport change. It is critical to knit communal open space to the public open space realm, to streets, pedestrian networks and adjacent parks. These extend out to all the blue–green systems of the city: bushland, recreation areas, tree canopy, waterways and urban drainage.

Precinct-scale benefits

The project considered the precinct scale in three case study suburbs (each examined in the Typologies Catalogue): Knutsford in Perth, Salisbury in Adelaide and Norman Creek in Brisbane. This demonstrated key benefits of precinct-specific infill such as allowing for seasonal overland flow in floodplains between flooding and drought, the daylighting of existing buried creeks to become new green corridors or precinct-scale water storage opportunities.

Improving city-scale ecosystem

Even in the context of a single city, there are cities within cities and systems within systems. Within one city are many vegetation types, soil types, rainfall, microclimates and each have their own design requirements. This has been the subject of continuing design research in Perth [5].

The blue–green systems of Perth are within one of 36 global biodiversity hotspots - regions of extreme value to human and ecological health that are in conflict with human impacts, including infill housing. Ecological mapping across Perth has uncovered ‘flashpoint’ areas, where housing will have substantial ecological impacts unless planning and design changes course.

As a global epicentre of rich and diverse ecology, finding the pathway of repair out of these urban–biodiversity conflicts is urgent [6]. We must work to take an ecological focus to understand precinct-scale and precinct-specific strategies.

In these sensitive ecological areas, that have many surrounding Threatened Ecological Communities, there is need for highly considered infill design and precinct regeneration. Specific strategies are being developed for coupling ecological care and repair with urban regeneration. Many of these ‘conflict zones’ between urbanisation and ecosystems are a decade or more away. To ensure good outcomes, planning is needed now to couple urban regeneration with a serious agenda for ecological regeneration. These contexts require forward planning, strategic approaches and coordination.

This project paves the way for informing policy in many states and setting performance targets for development assessment [7]. How these new approaches are handled from a planning perspective is crucial. The work asks us, as planners, designers and researchers to raise design and performance criteria in planning, to design more nuanced and coordinated precinct planning controls and to cultivate a more connected concept of urban and environmental issues.

AUTHOR ACKNOWLEDGEMENT

The project team has been led by University of Queensland water scientists Steven Kenway and Marguerite Renouf and architects and urban designers Nigel Bertram (Monash University) and Geoffrey London (The University of Western Australia) with Beata Sochacka, Oscar Sainsbury, Shenbagameenal Surendran, Mojtaba Moravej, Kerry Nice, Tatjana Todorovic, Niloofar Tarakemehzadeh and Daniel Jan Martin. The author is a doctoral candidate at the CRC for Water Sensitive Cities.