Everyone claims to build green buildings, advocating energy efficiency and ‘sustainability’. However, Australia’s buildings fall considerably short of actually achieving their energy star-rating, and have detrimental building defects that lead to significant structural and health implications, hence making a mockery of sustainability credentials. Australia, please wake up.
The challenges emanate from ‘dew-point-shifting’. In response we present the four core elements of the European ‘Passivhaus’ standard, a voluntary building standard that effectively leads to super-performing ‘architectural esky’ buildings. In future articles I will discuss results from better insulating and air-sealing of buildings, and also the importance of high-performance windows, including triple-glazed windows. Windows remain the weakest point of the thermal building envelope by far, even with ‘Passivhaus’ buildings.
The local building codes of Australia demand that buildings are better insulated and more airtight. However, while still applying conventional building techniques and materials, we ignore the fact that the dew-point gets shifted into our building envelope and that moisture is trapped in walls and ceilings. This results in interstitial mould formation, which in turn leads to structures rotting invisibly and ultimately generating respiratory health challenges for occupants.
Every residual building gap (e.g. around windows, doors or structural beams, and at skirting boards, light switches and power points, down-lights, kitchen cabinets) becomes a focus-thoroughfare for cold air ingress and/or moist warm air exit. Similarly, structural steel beams and concrete slabs as well as walls become significant thermal bridges between indoors and outdoors, all leading to moisture condensation within the building envelope.
In the last 30 years knowledge about building physics and truly effective solutions were developed in Europe and have passed on to the entire suite of building professionals. Europe now rolls out Passivhaus buildings as a standard matter and at no extra costs – poised to last and perform well over hundreds of years.
What does Passivhaus mean?
The German word ‘Passivhaus’ translates as ‘passive house’ in the context of the building’s reaction to the weather. Passivhaus, however, is not to be mistaken for the better-known term ‘passive solar’, which relies heavily on the benefit of winter-sun exposure and lots of thermal mass for (potential) warmth.
Passivhaus buildings in contrast work with any architecture. They can be lightweight, any shape or size, and even without solar exposure. These buildings behave just like eskies. They are perfectly insulated as well as air-tight (sealed) all around the building envelope. Unless windows or doors are opened, neither cold, heat, rain, wind nor noise are felt inside. The building therefore needs effectively (almost) no heating or cooling, all year round, almost irrespective of climate zone.
However, as Passivhaus buildings barely loose heat, solar heat gain control of windows is paramount. To keep unwanted sun out, this calls for external shading, preferably via active devices such as external blinds, screens or shutters. Solar-control glazing (tinted glazing) is omitted as invariably too costly and superfluous.
Fresh air and energy rating
Fresh air is supplied to the entire house by a comfort ventilation system during weather periods when windows and doors are better not opened for thermal or humidity reasons. The comfort ventilation package includes a high-efficiency energy recovery ventilation unit and an integrated miniaturised reverse-cycle air-conditioner/heat-pump system.
The specific heating and cooling design loads of Passivhaus dwellings are both limited to, and easily achieve, 10 W/m2. For example, a 250m2 five-bedroom family home runs on a single 2.5-kWth/R reverse-cycle air-conditioner/heat-pump unit. Translated to the Canberra region, the real performance of a Passivhaus is around a true 9-star building. The energy consumption of such a building is around eight to ten times lower compared to a calculation-rated 6-star design.
Adopting the basic Passivhaus toolbox allows architects to be free of design constraints while achieving extraordinary building performance and health. It took Europe over two decades to wake up, to understand how to build healthy sustainable buildings. How long will Australia take?
For more information visit www.laros.com.au.