What is Passive House/Passivhaus?
According to Felicity Bernstein of Melbourne Design Studios, it’s a ‘fabric first’ approach that makes the inside of a building pretty much independent of the outside climate. ‘A Passivhaus provides a stable internal temperature of around 22 degrees celsius all-year around, no matter what the outside temperature is, generally without relying on air-conditioning or artificial heating,’ she says.
‘It’s a more all-encompassing building standard, that also looks at health and comfort as well as building physics, condensation, indoor air quality and so on.’
Homes built to the Passive House standard use elements of passive solar design, which is all about optimising your environment by harnessing the sun for heating, whilst also mitigating summer radiation. That’s why sustainable homes in Australia tend to feature big northern eaves, double-glazed windows, and concrete and brick features that provide the home with thermal mass, because they can absorb, store and release heat well.
This means a building can rely on less active heating and cooling systems, and more ‘passive systems’ that are managed by the home’s residents: for example, opening and closing windows, or operating window shading as required to help cool or heat the home. But this isn’t the only thing that makes a home a passive house!
What are the main principles behind a Passive House?
Passive House design relies on five core principles:
Thermal Insulation ensures the home has an efficient ‘envelope’ around all the home’s floors, walls, and roofs. Altereco director James Goodlet says the quality of insulation required depends on the climate of the home’s location.
Airtight construction (which prevents air-leakage) is a requirement for passive homes, because ‘air leakage’ is one of the main contributors to an uncomfortable (and potentially unhealthy) house, creating pathways for moisture to travel, and mould to grow, James says. ‘To verify the air leakage in a Passive House, a building is pressure tested – also known as a blower door test – measuring how many times per hour the air volume within a building completely exchanges.’
High Performance Windows. ‘Windows are the weakest part of the thermal envelope, so critical consideration to window and external door design is imperative to meeting the standard. There are numerous manufacturers now in Australia creating passive house windows, however there is also a strong market of windows being imported.’
Thermal Bridge Free Construction. A thermal bridge – also known as a cold bridge – is a weak spot in the insulation where heat transfer is much higher. This could be due to a break in insulation or if the insulation is interrupted by a material with higher thermal conductivity, such as wood. ‘Picture the inside surface of an aluminium window, which then drips onto a timber reveal and mould grows,’ James explains.
The final principal, Heat Recovery Ventilation, (HRV) is ‘an essential addition that ensures that fresh, filtered air is distributed through the home, and that stale air and moisture are extracted from the home, maintaining an optimal relative humidity range. The heat recovery component ensures that energy loss is minimised.’
What are the benefits of a Passive House?
Passive houses by nature are sustainable and extremely low-energy, meaning they hold plenty of long-term savings for your energy bill.
‘Passive houses can save up to about 90% of the energy that a traditional house uses in this climate. Depending on your habits, this could be several thousand dollars each year,’ Felicity says.
‘Traditionally, in Victoria we use approximately 70-80% of operational energy for heating, and 20-30% for cooling. A passive house easily gets rid of pretty much all heating requirement and can reduce the cooling component substantially.’ And with the addition of solar panels, homeowners of a Passive House can easily turn their home into a zero-energy home, doing something good for the environment while saving substantial money each month!
Marc Bernstein-Hussmann adds that they also offer a number of significant health benefits, thanks to the better indoor air quality, while rigorous testing processes means they will have a higher quality construction than the average home, preventing mould and the home’s longevity.
‘I like to compare it with living in a tent vs keeping your food at the temperature you want it in an esky,’ Marc says. ‘Traditional houses are often quite drafty, and the indoor air is at a similar temperature to the outdoor air unless actively heated or cooled’.
‘However, these days most people expect more from their houses, and have huge energy bills to keep their house comfortable. This is where passive house provides such a huge benefit.’
Is it more expensive to build a passive house? What are the downsides?
Felicity says a passive house can be slightly more expensive to build, anywhere between 1%-15% more expensive – at least, for now. But with an increasing demand for passive houses, she expects the market will catch up sooner rather than later.
James says the only downside of passive houses is that when a passive house gets hot, it will take longer to cool. But the occupants can help this process by knowing when to open and close blinds and windows, letting hot air out and cool air in. He also notes that the certification process by a third-party like the Passive House Institute to get a build accredited can also be ‘quite onerous’ and come at an extra cost.
Do all passive houses have to be certified?
In short, no. ‘You can build a Passivhaus in Australia without having it certified, as long as your modelling, the so-called Passive House Planning Packages is correct, and you’ve employed all the five principles correctly and have airtightness tests done,’ Felicity explains. She says it can be quite difficult for someone who isn’t familiar with the ins and outs, so it’s best to get a Certified Passive House Designer and also Certified Passive House Trades on board to work through this for you!