While is it fairly easy to grasp what Passive House is about, it remains a little abstract for those who have not had the opportunity to design, build, live or occupy one. Here is a list of frequently asked questions that can hopefully assist in filling in the blanks. Got a question not answered here?….please drop your question into the comment box below and we will get back to you soon.
Why are conventional Australian houses significantly less efficient and why do they end up costing so much more than Passive Houses?
Three words…minimum building code! More specifically, insufficient insulation detailing, vapour barriers that are inevitably punctured, uncontrolled thermal bridging, poor quality windows (80% of the market is single glazed!) and dated construction techniques. To summarise, poor building envelopes! To make up for these subpar practices, air-conditioners and heaters are required to make up for all of that energy loss which ends up costing homeowners each and every year.
Isn't a Passive House a complicated, high-tech building?
The technology employed in Passive Housing is tried, tested and completely user friendly. In conventional building, most have separate heating and cooling systems that require programming. At its foundation, Passive Housing is a simpler technology that regulates ventilation and air-circulation rather than the production of heat and cold through more artificial means.
Will I have to source building materials internationally?
While a trip to Bunnings is likely to lead to disappointment, materials are now available locally and are growing by the day. There are a number of certified suppliers based in Australia who work specifically with Passive House Designers and Builders.
What is a ‘thermal bridge’?
The calculations around Thermal Bridges are rather complicated and intricate, but essentially, thermal bridges are the points at which conventional housing design lose energy. They are often unaccounted weak points in the building fabric resulting in high local discomfort, moisture and mould while providing a highway for energy loss. Passive House design specifically addresses thermal bridges in order to maximise energy efficiency unlike any other standard.
Can I be sure that my Passive House will ‘work’?
Absolutely. But it is essential that your project has been properly designed in PHPP, supported by a Certified Passive House Designer or Certifier and then well-executed on-site by Certified Passive House Tradespersons. There are over 80,000 Passive Houses of all building types throughout the world, providing very high levels of comfort in various climates. The ‘Lucky Country’ of Australia is easy by comparison!
Do I need professional assistance to achieve a Passive House?
Yes. In order to achieve the Passive House standard, it is vital that the building design is tested and verified using the specialist PHPP software. At present there are now over 90 Certified Passive House Designers and Tradespersons providing dedicated full Passive House services in Australia.
Is there a qualification or certification process for Passive House builders?
There is a certification process for Tradespeople available through the Australian Passive House Association or one of its partners. Individuals who complete the Passive House Exam must demonstrate a sound knowledge and application of the fundamentals of Passive House Construction. They are also expected to further their knowledge and development in Passive House.
Living in a Passive House
What is it like to live in a Passive House?
Great, Fantastic! A Passive House construction ensures a long, durable building life, that requires light-filled spaces and high levels of comfort. Combined with extraordinary low heating/cooling bills and excellent indoor air quality, Passive House buildings also provide a major opportunity to reduce your carbon footprint. It is very quiet too, due to the well-sealed building envelope.
Are Passive Homes comfortable?
Extremely comfortable, so comfortable that Passive Homes are often designed without a heat source even in Canada and cooling in warmer climates. Typically, the heat from residents combined with internal equipment and passive solar heat entering the building are enough to markedly improve comfort. Due to the well-sealed building envelope, all that is required is a relatively basic ventilation system which supplies fresh air making for superior air quality without causing any unpleasant draughts.
Summer or winter, you can be assured that your Passive House Building will provide a maximum level of comfort with reasonable construction costs – something that is repeatedly confirmed by Passive House residents.
Can you open the doors and windows?
Don’t believe the hype! Passive House buildings are extremely comfortable in all seasons, with windows being a major comfort component. While it is true that Passive House Buildings are designed so there are no drafts, temperature variance is extremely narrow (even near doors and windows), and active, balanced ventilation makes for superb indoor air quality, this does not mean we cannot open windows on a beautiful day or when it gets stuffy! Simply put, while your often don’t need to open them because Passive House Buildings are designed around the occupants comfort, a user will know best!
Passive buildings are super airtight – what about moisture and mould problems?
Passive buildings do require an extremely airtight building envelope, perhaps 25 times tighter than a conventional building in Australia. Does this lead to moisture and mould? Well, without adequate ventilation, insulation and an airtight barrier it would but of course, this is exactly how Passive House Buildings must be designed.
With constant, low-level ventilation a major preventative of moisture problems in addition to maintaining excellent air quality, Passive House professionals are highly aware of designing out moisture and mould and can often undertake detailed modelling (if required) to identify and address potential moisture issues with a variety of techniques during the design.
Is it unhealthy to occupy an ‘air-tight’ building?
It is probably truer to say it is more unhealthy living in a draftee space typical of Australian buildings. One of the main benefits of Passive House buildings are the high air quality as a direct result of air-tight design that allows the controlled provision of lots of fresh air via a balanced ventilation system. In normal buildings, fresh air enters the building through a series of vents and through infiltration or drafts. However, such means of ventilation is uncontrolled and you cannot be sure that all spaces at all times are being properly or sufficiently supplied with the correct amount of fresh air. Indeed, as the entire volume of air in a typical Passive House is changed on average between 8 to 12 times per day (depending on the setting of the system) ensuring very high air quality throughout, plant growth is known to flourish, a sure sign that things the space is healthy!
Is the ventilation system noisy?
The ventilation system itself is housed in a very well insulated and airtight cabinet which is normally positioned in a utility room. The noise from the fans is no greater than that from a modern fridge. The ducting is fitted with what are referred to as ‘attenuators’ and combined with acoustic insulation, which reduce the sound of air passing through the system. In bedrooms, if designed correctly and properly fitted, air passing through the system should be barely audible at normal flow rates.
What happens if there is a power-cut?
Similar to normal houses, all mechanical systems will cease to work. However, because Passive House Buildings are so well insulated, they will maintain a higher level of comfort for much longer than would a normal house in the event of a power failure. If the power cut lasts for a prolonged period (say, more than 12 hours), then the windows can be opened to provide fresh air if required.
Carbon monoxide alarms can be fitted in the house to detect reduced air quality.
Can I have an open fireplace in a Passive House?
The answer from an Australian perspective is very likely to be no. Having an open fireplace would introduce too much heat into the space and may dramatically reduce the efficiency of the mechanical heat recovery ventilation system (due to lack of airtightness). However, there are other really clever means of having a real flame effect in your Passive House, including bio-ethanol fires as well as wood burning boilers or stoves with glass fronts. By the way, if you have young children in the house, please reassure them that Santa Claus knows Passive House Buildings very well and he uses the ventilation system and some magic dust to bring the gifts for Christmas morning.
How does it work?
How energy efficient is a Passive House?
Passive Houses are designed to be incredibly energy efficient, up to 90% more efficient than a typical Australian home (cooling + heating). With a high level of insulation and an airtight building envelope, the key to the design is to minimise heat loss/gain and control annual solar heat gain. By designing building envelopes that incorporate “thermal bridge free design”, energy loss is significantly reduced around windows, exterior doors, mechanical openings, corners of the building and junction points in between the roof and the walls. Using high quality windows (minimum triple glazed) and insulated exterior doors are an absolute must in a Passive House.
How is a Passive House heated and cooled?
A Passive House takes advantage of the largest free source of energy on the planet, the sun. By orienting the main windows in the building to face north, there is a significant amount of energy gain within the space. Along with the heat given off from the occupants and appliances, this is often all that is required to keep the home comfortable year round.
A ventilation system is still required to provide fresh air throughout the home. The ventilation system transfers fresh air into the home from the exterior while a heat exchanger extracts the wasted heat from the air that is exhausted to the exterior. The excess heat is then recycled within the heat exchanger unit to heat the fresh air coming into the home.
Cooling a Passive House Building relies on its super insulated shell and the airtight building envelope which prevent the sun from heating up the space. Designing the roof to have large overhangs, operable shutters on the windows and even light cladding colours are all basic strategies that when coupled with effective natural ventilation ensure that a Passive House Building is cool throughout the hot summer months.
Do Passive House buildings use solar panels, geothermal systems and wind generators to achieve their excellent energy efficiency performance?
The thermal performance or the efficiency of a building, and the energy source or technology used supply heat or electricity, are two different things. Renewable energy systems do not affect the thermal efficiency of the house itself. In a Passive House building the primary goal is to achieve a superbly well-insulated and tightly sealed building envelope, then introduce fresh air via a very high-efficiency heat recovery ventilation system. Renewable energy technologies can be used on Passive House buildings that want to go the extra mile and go beyond Passive House Classic certification.
My builder says putting more insulation into a house than that required by the Australian Building Code is uneconomic.
When you continue adding insulation to a building beyond what seems economic, there is a definable level of efficiency where a full-sized furnace is no longer required because sufficient heat can be delivered to the building by other means. This allows capital cost savings to be realised on the heating and cooling system. Savings that can be put towards extra insulation and higher efficiency windows. This “definable point” is how the Passive House Standard is measured and achieved.
Why do you need a ventilation system in a Passive House Building?
A lot of energy is required to heat air, or cool it during summer, yet very little energy is needed to move air around via an efficient fan. Therefore in order to achieve low energy use in a building, air leakage has to be minimised or the heating energy you pay for just ends up leaking outdoors. All Passive Houses must achieve a stringent airtightness requirement. Certified Passive House ventilation units have exceptional energy efficiency and are highly recommended.
Wouldn’t a Passive House building overheat in summer with lots of insulation and north facing glass?
One of the design requirements for any Passive House Building is to ensure summer comfort. Buildings must be designed with appropriate summer shading on north facing glazing in particular. In areas of high summer temperatures where cooling loads predominate, it often becomes necessary to minimize east- and west-facing glazing, as well as using spectrally selective glass to reduce summer overheating. As the amount of glazing, like every other building component, is determined with the Certified Passive House Designer and PHPP software, it is important to get them involved early so all client requirements can be met.
How does Passive House construction differ from regular construction?
In many ways Passive House buildings can look similar to typical, local buildings. As the industry grows, so do its professional and material suppliers that will continue this trend where you cannot distinguish between a non-Passive House and Passive House Building. However, underneath their skin they distinguish themselves with a few key features.
- They often use larger quantities of thermal insulation to create a deeper but more thermally resistant envelope.
- Junctions in the envelope are carefully designed to avoid thermal bridging, air-leakage, and drafts.
- They have state-of-the-art windows, usually high-spec thermally broken units which typically have triple glazed, gas filled glazing to keep a tight control on heat loss/gain.
- Ventilation is achieved with the help of a Mechanical Ventilation Heat Recovery (MVHR). This removes heat from exhaust air, and uses it to heat incoming air to maintain a stable indoor temperature.
Do I have to have lots of north facing windows for the Passive House to work?
Not necessarily. Sure enough, it is ideal to have north facing windows to harvest the free energy provided by the sun. However, it is also possible to achieve the Passive House standard if your site does not lend itself to maximising solar gain (but you will probably have to compensate for this with additional insulation). All designs have to be tested and verified in the Passive House Planning Package (PHPP) software. If you have a wonderful view from the southern side of your house, you needn’t deny yourself of this. The Passive House is not as rigid as many people think, particularly in the Australia’s moderate warm to temperate climate.
Do you need a special site type if considering building a Passive House Building?
No, generally not. Of course, it is ideal to be able to design the building to face north, and to avoid over-shadowing by coniferous trees or local buildings. However, if these conditions do not exist on your site, then don’t worry. Allowances can be made, and tested in the PHPP software, for any shortfall in terms of ideal orientation leading to reduced solar gain.
What is the best insulation to use for a Passive House?
There are no strict rules in this regard. The critical issue is to achieve the U-values (thermal performance) required as identified by the PHPP. Thereafter, you can use whichever insulation type you prefer or can afford, whether polystyrene, cellulose, polyisocyuranate, strawbale, sheep wool and so forth. Some insulation types are better performing than others, requiring thinner walls, whereas other are less efficient and will require thicker walls.
Does a Passive House have to have thick walls?
Generally, yes. A Passive House Building needs more insulation than a typical building, and this is generally achieved by having significantly thicker walls. The thickness of walls depends on the U-values required which in turn is greatly dependant on the performance of the insulation, the type of construction (whether concrete, timber frame, etc), overall design, orientation, compactness and so forth. You generally won’t notice the thick walls from the outside of the house, however, as the windows are placed in the insulation layer which is best placed towards the exterior of the building shell.
Is it necessary to have triple glazed windows in a Passive House in Australia?
It really depends on your location and thus the climate. All Passive House’s must be designed and tested using the specialist software PHPP and you might find, on occasion, that it is possible to use very high performance double glazing in some instances. If you do use double glazing, however, be aware that you will probably experience some thermal discomfort on very cold winter nights in mountainous regions whilst sitting close to such windows due to the temperature difference that will inevitably arise between the internal surface of the glass and the surrounding living space.
How do Passive Buildings look?
Can you build large buildings to the Passive House Standard?
Yes, any type of building can be built to the Passive House standard, including skyscrapers. In Europe there are Passive House schools, office buildings, supermarkets, retail centres, gymnasiums, health clubs, and thousands of Passive House apartment units. The largest current development is the 26 story Cornell University Campus in New York, which will house 520 people, built and certified to the Passive House Standard.
Does a Passive House have to follow a strict design style? Does it have to be modern?
With the right team in charge, passive design does not dictate aesthetics. A Passive House can be traditional or contemporary but the key to a Passive House is the simplicity in its plan. It is best (most efficient and cheapest to construct) to create a compact shape (two storey is more efficient than a bungalow) with optimal solar gain, but the Certified Passive House Designer should otherwise be free to create any bespoke design according to the Client’s needs. It is important that the Passive House concept can be adapted to local cultures, styles and building traditions.
Does it cost more to build a passive building compared to a conventional equivalent?
In Australia, building energy standards are lower than in many parts of Europe, and it is relatively difficult to source some high quality components here. The extra cost will depend greatly upon design, size of project, quality of finishes and so forth, but typically a range of 10 – 20% should be prepared, assuming the builder has some experience and training in this type of construction. However, recent local social housing projects are suggesting very small additional costs.
The more large-scale window and door manufacturers bring high-performance products to the Australian market, economies of scale will drive down costs. The cost is usually offset by the massive reduction in energy bills, and the elimination of heavy mechanical heating and cooling units. With increasing energy prices, the question to ask yourself is ‘Can I afford not to build a Passive House’!
Are Passive Houses a good investment to live in?
Absolutely, with a 90% reduction in annual heating/cooling fuel consumption the energy savings will cancel out much of the increased up-front investment cost of increased insulation, better-quality windows and ventilation systems. Building a significantly better quality, smart home is a hedge against rising energy prices in the future. Above and beyond the cost savings, a Passive House owner also enjoys better indoor air quality and overall comfort…a factor difficult to include in the good investment equation!