Concrete a key component of Australia’s first Passive House apartment building

Sustainability architects have for many years specified concrete for its thermal qualities, and it’s clearly an essential part of construction – especially in mid to high rise buildings and infrastructure. In recent times it’s attracted the attention of the Passive House movement.

Concrete has long been heralded for its versatility, appealing price point and recyclability. It’s also fire proof. 

Architects in particular hail its ability to deliver longevity, which is key to the sustainability principle of “long life, loose fit, low energy“. Loose fit design means that interiors to be reconfigured or refurbished when needed, but the base building should in theory last “100 years”, a lifespan that concrete can deliver. 

Now the material has also been embraced by the one of the more sustainable building methodologies to emerge in recent years, Passive House (or Passivhaus). In particular, Australia’s first Passivhaus-certified apartment building, The Fern, recently completed in the inner Sydney suburb of Redfern, has used concrete as a solution that helps deliver the air tightness and temperature control that is central to Passive House.

It’s a good story for concrete that has come under scrutiny over carbon emissions, at least at the point of production, and other environmental concerns that face the construction industry in general. 

These pressures have not been ignored and researchers have worked had to lessen concrete’s environmental impact by using less cement and more recycled content such as fly ash or waste plastics,  and more efficient design to reduce structural materials.  

With Passive House it’s the inherent nature of the material that is proving its value, able to deliver a comfortable interior temperature with very little energy used in heating or cooling, plenty of ventilation without uncomfortable draughts, and the additional benefits of being sealed against pests such as cockroaches and vermin. 

It delivers these benefits by sealing the building envelope, controlling air movement through a heat exchanger and using insulation to prevent heat transfer through the walls. 

Advocates claim that Passive House dwellings typically use around 10 per cent of the heating and cooling energy of the average house. Given that most of the carbon emitted from a building comes from its operation and use, the impact of carbon emissions from concrete construction ends up being a small part of the building’s overall output.

According to a report from the Centre for Design (CfD), at the School of Architecture and Design, RMIT University, building operation “contributes to between 75 per cent and 96 per cent of environmental impact, depending on the impact category and the building considered”.

And the long-life of concrete buildings further reduces the carbon impact when it is amortised over the life of the building. 

The Fern, in Redfern, open for short term rental

In constructing The Fern, architect and builder Oliver Steele, of Steele Associates, specified in situ concrete construction for slabs and walls. Only 3-point Greenstar certified concrete was used, with maximum available recycled content, for this Ultra-eco development. 

And although principally chosen for its structural, acoustic and aesthetic qualities, it has, according to Steele, delivered several unexpected benefits.

“We noticed that while construction continued through summer the building stayed quite cool,” he says. “I think that was partly because of the thermal mass of the concrete slabs and walls.

“But the great benefit we’ve found with concrete construction is its airtightness, which is a key factor in the Passivhaus system. It’s quite difficult to achieve airtightness with framed structures because you’re essentially starting with a series of openings that need to be covered and sealed.

“Because concrete is monolithic, that’s not an issue. Even the cold joints between the walls and slab are inherently airtight.

“I was hoping this would prove to be the case, and it’s been borne out with all the blower-door testing we’ve subsequently done.”

Steele says service penetrations also proved not to be a problem, with a simple sealant used around fire collars to achieve the required airtightness.

Internally, concrete walling has been exposed through the living and bedroom areas, with the form lines and bolt holes adding to the character and sense of solidity. 

A reusable modular steel formwork system was used to construct these in situ walls. The vertical joints are at 600mm centres, and the concrete surface has been hand-finished with Carnauba Wax to create a natural sheen.

While The Fern achieves some passive solar benefits from its east-facing aspect, its urban location also comes with some compromises. 

“The cornerstone of good passive solar design is orientation,” Steele says, 

“If orientation is imperfect – as is so often the case in urban environments – the passive solar concept is compromised. “Passivhaus overcomes this challenge, creating a well-insulated, well-sealed, temperature-stable interior, kept fresh with heat recovery ventilation.”

Steele says he and his team have worked for five years to make The Fern an “exemplar of sustainability”, while at the same time setting a high benchmark for quality, form and function. “We considered every element of the building from first principles, and rigorously interrogated the apartment typology, taking nothing for granted. All our decisions were driven by quality and sustainability,” says Steele. 

Each of the apartments boasts a sheltered balcony, bespoke furnishings and a palette of warm, natural finishes and materials, including concrete.

Another distinguishing Passivhaus feature of the development is Heat Recovery Ventilation (HRV). HRV delivers constant filtered, fresh air to living and sleeping areas while extracting stale air from kitchens and wet areas. An inbuilt heat exchanger swaps the heat from incoming supply air to outgoing exhaust air in summer, keeping the interior space cool, while in winter it works in reverse to keep the warmth inside.

As well as creating thermal comfort, HRV makes for a quiet, clean, dust-free interior, which is a huge benefit in city dwellings. 

If you want to try Passive House living for yourself, The Fern serviced apartments are available to book now. 

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