Sustainable building is not and should not be limited to the construction of efficient new builds. If we are to reconfigure our urban environment to reduce its impact, it is also necessary to revisit our existing stock of residential and commercial buildings.

Faced with a tight footprint and strict planning controls on a heritage site, this challenge was exacerbated for Zen Architects when chosen for the renovation of a home in Melbourne’s inner north. The client for North Carlton Green House was determined to integrate gardens into every possible space within their home, even on a site where it was not possible to achieve a garden in the traditional sense.

The single-storey, two-bedroom, Victorian terrace house sits on a diminutive 166-metre site. Due to the small nature of the home – compounded by planning and heritage restrictions that limited the ability to build up – it was necessary to use most of the available space to maximise the floor area of the house. However, this desired increase in floor area would logically result in a reduced garden area; an aspect of the brief that the client was uncompromising on. Zen Architects’ solution was to blur the lines between what was house, and what was garden.

Although it doesn’t contain a typical outdoor garden space, greenery has been incorporated throughout the entirety of North Carlton Green House – top to bottom, inside and out. Inspired by their client’s “connection with the landscape”, Zen Architects created several building layers that acted as green space: courtyard, rooftop, and interior. In other words, in place of typological garden space, Zen made the entire house a garden.

“[We] identified our client's passion for the sun as an opportunity to harness passive solar design to minimize energy use,” says the architect in a design statement. “Her passion for gardening meanwhile would provide an opportunity to increase local ecological diversity in a typology where there is typically very little garden due to size constraints. Our client required the small site to be used to maximum potential to increase floor area of the house while also increasing the garden space.”

Two courtyards that flank the dining room contain garden beds that protrude into the house, assisted by oversized glass panels with natural wooden frames. A pond that sits within one of these inverted courtyards reflects light onto the interior ceiling, while planter boxes to the outskirts act as privacy screens.

These deep, glass-bound courtyards contribute to the home’s passive heating, drawing the sunlight deep into the floorplan. In summer, interior temperatures are stabilised by a curtain of tillandsia air plants, and a deciduous wisteria that engulfs the north-facing courtyard with shade. Extensive windows have been oriented to catch breezes over the pond, further enhancing the seasonal cooling effect.

A rooftop garden acts as an extension of both green space and insulation. While Zen Architects’ renovation of the property increased the floor area from 90 metres to 132 metres, it also managed to almost double the garden space – from 20 metres to 35 metres. The garden space that would have otherwise been lost to an increased floorplan was supplemented by a green rooftop. This space can be accessed internally via a bridge that floats above a two-storey, north-facing “void” over the first-floor mezzanine.

The shape of the roof is one of the defining characteristics of the building profile. A distinctive wave shape, the curve of the upper façade doubles as a reference to the site’s palm trees while appeasing restrictive planning controls. As it dips to the west, the roof is hidden from the heritage streetscape and prevents overshadowing to neighbouring properties.

As well as acting as “an oasis from the urban environment”, the rooftop garden coats the home with between 300mm and 600mm of insulating earth. Thermal mass has also been achieved through a robust concrete ceiling and exposed concrete floors. In summer, the void that sits underneath the rooftop garden facilitates natural heat removal through a stack effect.

In North Carlton Green House, “green” is evident in both senses of the term: through the ubiquitous garden spaces, and through the range of green initiatives that keep the home functioning sustainably. High-performance wall insulation, gas-boosted solar-hydronic underfloor heating, solar hot water and rainwater harvesting systems have all been incorporated to keep the home’s environmental footprint as small as the building footprint itself.

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