According to Australia’s 2011 Census, 88.9 per cent of Australians live in urban areas. Those areas are defined as the built-up areas of towns and cities of more than 1,000 people.

The Australian Capital Territory leads the pack, at 99.5 per cent urbanised, while the Northern Territory ranks at 73.8 per cent.

Growth over the coming decades is predicted to be robust, says the Australian Bureau of Statistics, with all major cities forecast to double in population by mid-century. The total population is expected to top 60 million by 2101.

This growth will put pressure on housing supplies, which already pose affordability challenges. The mean number of persons per household has been creeping up lately, with the figure at 2.59 in 2013-14. That’s a slight uptick from 2011-12, which was at 2.57 persons per household.

Besides rising prices, a strong trend in housing is the demand for walkable neighbourhoods. In contrast to multi-storey towers, this trend is about neighbourhood living, not necessarily city living. The concept of a walkable neighbourhood calls to mind tree-lined streets, local cafes, shops, and restaurants, and nearby schools, all in proximity to single-family homes.

Unfortunately, single-family homes gobble up land without creating the density that’s optimal for truly affordable, walkable neighbourhoods. Simultaneously, the demand for single-family homes has precluded the zoning changes needed to adapt to the demand for walkable neighbourhoods. Those changes include encouraging low-rise and multi-family buildings that can increase the density, or critical mass, needed to create walkable neighbourhoods.

Homeowners in single-family neighbourhoods have been vocal – and successful – in combatting multi-family projects in their neighbourhoods, partly because the proposed projects have been vastly different in form from the single-family dwelling.

A complementary type of development, however, called “Missing Middle Housing,” can help to solve those problems. The term Missing Middle Housing was coined by architect Daniel Parolek, principal at Opticos Design in Berkeley, California, to describe multi-family or clustered building forms that integrate into single-family neighbourhoods and enhance neighbourhood walkability and affordability.

The concept is not new, but has mostly been out of favour for decades as municipalities and developers have chosen to promote single-family homes in sprawling, auto-centric developments, as well as high-rise multi-family forms such as towers that have sometimes been crammed into older low-rise neighbourhoods. Low-rise, multi-family forms have been largely excluded from the single-family neighbourhoods where they could help create the walkable environment.

Missing Middle style housing offers several benefits to cities and residents, including greater affordability, greater variety, and greater efficiency. As Karen Parolek, principal at Opticos Design, noted in an article in Better Cities and Towns, cities across the country are in need of more affordable housing. The program provides more units on less land than single-family detached housing, smaller units can be cheaper, and more units on a single property can lower unit costs while still giving developers a reasonable profit. Furthermore, increasing density with space for local businesses can obviate the need for a car, further enhancing affordability.

According to Opticos Design, characteristics of Missing Middle Housing include:

• A walkable context
• Medium density but lower perceived densities
• Small footprint and blended densities
• Smaller, well-designed units
• Off-street parking does not drive the site plan
• Creating community
• Marketability

The Missing Middle model includes several building types:

• Bungalow court
• Side-by-side duplex
• Stacked duplex
• Townhouse
• Fourplex
• Multiplex
• Courtyard apartments
• Live/work
• Carriage house

Why has this housing form been relegated to the sidelines? Codes and zoning have played a strong role, while developers have looked for bigger and more profitable projects and homeowners have rejected multi-family forms in their neighbourhoods. Zoning districts, for example, often have a gap between single-family structures and larger, multi-family structures. According to Opticos, that gap is especially apparent “when the zones shift from upper (smaller lot) single-family zones that only allow single-family detached uses/homes and the lower end of medium density/multifamily zones that usually allow much bigger buildings.”

The Missing Middle model is the real-world application of form-based codes that specify the types of building forms that can be built in a neighbourhood and at what density, as opposed to the use of each building. This type of development holds promise for both older urban neighbourhoods that are walkable and have nearby amenities but need to increase density, as well as suburban neighbourhoods that are not presently walkable. The Missing Middle approach would integrate appropriate low-rise, multi-family dwellings into both environments, with developers and business owners able to use the structures as needed in that neighbourhood.

Furthermore, varied housing forms support people at different stages of life, enabling them to remain in their homes and neighbourhoods, whether that’s the urban or suburban context. According to Daniel Parolek, people of varied ages are interested in this type of housing, including “Millennials who do not want to live in single family suburban homes and want a walkable neighborhood, Baby Boomers who are downsizing and want and need to live in a walkable community.”

Many Baby Boomers, in particular, are more attracted by walkable neighbourhoods, rather than price.

“They often want quality over quantity as well, so small units do not necessarily mean cheap,” Parolek noted.