Frequently Asked Questions
Is Passivhaus the same as passive solar design?
Passivhaus (or Passive House) often gets confused with passive solar design, but there are some subtle yet fundamental differences. Passive solar design strives to maximise solar heat gain, and relies heavily on north facing windows, thermal mass and natural ventilation. Passivhaus adopts a fabric first approach, where windows, insulation and airtightness are all of the highest standard. Fresh air is supplied by mechanical ventilation which incorporates a heat recovery process to retain heat which would otherwise be lost. These features ensure that Passivhaus buildings lose very little heat. They rely much less on solar heat gain, so orientation is less critical. Passivhaus can be an effective solution for sites where solar access is less than ideal.
Passivhaus is much more than just ‘rules of thumb’. The design must be verified and the construction must be tested to ensure that the stringent comfort and energy criteria are met.
Is Passivhaus necessary in Australia’s climate?
Which climate? Australia has so many different climates. The Passivhaus standard may have originated originated in Germany, but it is growing internationally. Thousands of Passivhaus buildings in some 45 countries across the globe demonstrate that it is applicable in almost all inhabited climates. There is over one million square metres of certified Passivhaus floor area worldwide. Some 3,000 certified designers. And the design software is available in 25 different languages.
Passivhaus is relevant everywhere because the laws of physics don’t change. And neither do the requirements for comfortable and healthy indoor living conditions. Designing to the Passivhaus standard requires the use of certified local climate data. Rather than the somewhat ‘one size fits all’ approach of Australia’s construction code.
Is Passivhaus expensive?
Passivhaus and conventional construction are like apples and oranges. Passivhaus is a quality assurance standard which requires investment in high quality building components. The windows are of exceptionally high performance. There are increased levels of insulation. And excellent workmanship is required during construction in order to achieve the stringent airtightness criteria. These features cost more up-front, but Passivhaus is designed to be affordable over the long term. Expensive heating and cooling systems can be eliminated, ensuring significantly reduced running costs over the life of the building without compromising on comfort.
“Price is what you pay. Value is what you get.” - Warren Buffett
What is it like to live in an air-tight building?
Passivhaus buildings are renowned for having excellent indoor air quality. They are many times more airtight than conventional buildings, ensuring the air quality can be closely controlled. A mechanical ventilation system supplies 100% fresh, filtered, outside air throughout the occupied spaces. At the same time, stale air is exhausted, reducing the concentration CO2, VOCs and excess moisture.
Passivhaus targets a range of 40-60% relative humidity, generally accepted as comfortable and healthy for indoor environments. Relative humidity levels which are too low feel dry and can lead to respiratory problems. And high humidity can contribute to mould growth, dust mites and fungus, making it dangerous for people with asthma and allergies. Achieving these comfort and health criteria with natural ventilation alone would be impossible.
Is mechanical ventilation noisy & expensive to run?
Mechanical ventilation with heat recovery (MVHR) is a key component in achieving the Passivhaus comfort and energy criteria. Mechanical ventilation is essentially just fans which remove the stale inside air, replacing it with fresh outside air. But in winter when this outside air is cold, it then has to be reheated. Passivhaus ventilation systems incorporate a heat exchanger, which retains the warmth from the inside air and uses it to preheat the cold outside air being brought in.
A properly installed MVHR system is very quiet, with highly efficient fans running at much lower air speeds than conventional air conditioning. It retains around 90% of the heat contained in the stale air extracted from kitchens and bathrooms. So even when operating 24 hours a day, it can save over ten times as much energy as it uses.
Can i open the windows?
Passivhaus occupants can open their windows whenever they choose. The benefit of Passivhaus is that when it’s too hot or too cold, or too noisy, or if security is a concern, or if someone is sufferring from allergies…it’s simply not necessary. The mechanical ventilation system running in the background is usually far more effective at bringing in a continuous supply of fresh air so that it doesn’t ever feel stale or stuffy.
Common sense and individual preference will determine whether windows are opened or not. If it is cold or warm outside, it is likely best to keep the windows closed. But if it’s a cool summer evening, opening the windows can often assist the ventilation system to expel any built up heat. But as with any house, leaving the windows open in winter will result in cold draughts.
Is triple glazing required?
Passivhaus design considers the entire building envelope holistically, and not just individual components in isolation. The overall energy balance is what is important to understand. This means that the heat gains must offset the heat losses. The European climate generally requires the use of triple glazing. But double glazing would often be adequate in the milder climates of Australia. If you choose to import windows from overseas, you may find that the premium for triple glazing isn’t significant.
Passivhaus is not a prescriptive design standard. It recognises that every project and every climate is different. Many designers intuitively understand the climate in which they work, and whether their design decisions will affect the performance of the building in a good or a bad way. Passivhaus enables the designer to actually quantify the effects of these decisions. If necessary they can then modify the design or the individual component specifications accordingly in order to achieve an overall energy balance, and a cost-effective design.
“The whole is greater than the sum of the parts.” - Aristotle
Is heating required?
Just as a thermos flask keeps a hot drink hot, Passivhaus buildings are extremely good at retaining heat. But this heat still has to come from somewhere. Most comes from passive sources such as the sun, human occupants and household appliances. In colder climates a small amount of active heating is required in addition to the passive heat gains. But because Passivhaus buildings retain so much heat, their active heating requirements are substantially less than what would be required for conventional construction. Traditional ducted heating and in-slab hydronic systems are unnecessary. The equivalent of a hair dryer is often enough to meet the heat load of an average sized house.
Do Passivhaus buildings overheat in summer?
Overheating can be a problem in highly insulated buildings, just as it can be with poorly insulated buildings. Passivhaus buildings maintain very stable internal temperatures throughout the year, even in hot summers. One of the key performance criteria is that internal temperatures do not exceed 25°C for more than 10% of the hours in a given year. Some consider this frequency to be too high, and argue that Passivhaus designers should strive for a maximum of 5%, or even no overheating at all. This seems like a sensible approach when considering the potential effects of climate change over the next few decades.
The benefit of Passivhaus is that the risk of overheating can be tested early in the design process. That way it can be minimised or ideally eliminated altogether. It’s important to discuss your expectations and your tolerance to high temperatures with your designer. For many climates it is entirely appropriate to incorporate small active cooling systems if heat wave conditions are a concern.
Why do Passivhaus buildings often look the same?
The vast majority of Passivhaus buildings are located in Europe. Primarily in Germany, Austria and Scandinavia. These buildings generally have a traditional style, appropriate local context and construction methods. So it’s not surprising that there is a perception that Passivhaus must look a certain way. But they don’t have to. There are many recent examples of modern, contemporary buildings in various climates across the globe, including Australia.
Passivhaus does not prescribe a particular style of building. However, building physics tells us that simple and compact forms lose less heat than those with larger surface areas. This is why we curl up in bed if we’re cold during winter. As long as the Passivhaus performance criteria are met, you are free to use whatever materials and construction methods you choose. Just be aware that complex geometries, cantilevered balconies and floor to ceiling windows aren’t going to be the most cost effective design solution. The only thing limiting your Passivhaus aesthetic is your imagination.
“Simplicity is the ultimate sophistication.” - Leonardo da Vinci
