A Passive House is designed to have a stable indoor temperature of between 20oC and 25oC all year round, but needs very little energy to heat or cool. They are renown for being comfortable and healthy to live in and cheap to run.
Sound too good to be true? Jeremy Gates, our Managing Director and a certified Passive House Tradesperson, gives an overview of how Passive Houses are different and why build one.
The Passive House (Passivhaus) Institute was founded in Germany in 1996 and Europeans have been successfully building Passive Houses for many years. In Australia, interest in Passive Houses has been growing and the number of Passive Houses being built here is snowballing.
There are rigorous standards that must be met before a house can be certified as a Passive House. The 5 basic principles are:
- Thermal Bridging
- Heat Recovery Ventilation System
All 5 principles must be correctly incorporated into the building, otherwise the building will not perform to its full potential. Although the Passive House principles are most commonly applied to new buildings, they can also be adapted to renovations.
In a Passive House, windows provide light and free heating in winter. By ensuring that the size of the windows is appropriate to each orientation, solar radiation can heat the home during the winter months but not let too much heat in during summer.
Also, the windows must be airtight (windows are traditionally the weakest link in the building envelope, allowing warm/cool air to escape/enter the home). In colder climates, the windows in Passive Houses are triple glazed. In Australia, low-emissivity double glazed windows can be used. In order to ensure that heat doesn’t escape/enter the home through the window frame, frames must be thermally broken or non-metal (eg uPVC) and there cannot be any gaps around the windows. There are no leaky windows in a Passive House.
A Passive House must be air tight.
There are two airtightness layers – an internal layer and an external layer. The internal layer is to stop warm/cool air leaking out of the house. The exterior layer is a waterproof layer and is to stop water coming in. Both layers must be continuous with no breaks or holes. This requires meticulous attention to detail by the builder. Making the building air tight means no more draughts!
The floor, walls and roof of the house must all be insulated with no gaps or breaks. The floor must have a minimum level of insulation of R4, and the walls and roof a minimum of R6. There is no rule on the type of insulation you can or cannot use eg polystyrene, earthwool etc. However, some insulation types perform better than others, with better performing products meaning that the walls can be thinner compared to the less efficient products.
The insulation not only needs to meet the minimum level, it also needs to be continuous. So penetrations through the insulation must be kept to an absolute minimum.
Thermal bridges are areas of a building where energy (heat or cool) can transfer directly from the inside of the building to the outside of the building (and vice versa). In a Passive House, all thermal bridges must be eliminated. This can be done by the use of insulated construction materials or by incorporating thermal breaks to prevent the direct transfer of energy.
For example, aluminium window frames can act as a thermal bridge and so can only be used in a Passive House if they are ‘thermally broken’.
Heat Recovery Ventilation System (HRV)
In a Passive House, the HRV is the ‘lungs’ of the house. This ventilation system is essential because the house is completely air tight. The HRV runs 24 hours a day and provides a constant supply of fresh air into the house, and extracts stale air from the house, whilst keeping the indoor temperature at between 20oC and 25oC. It’s like opening your windows without losing the heat/cool from inside the house. That is because HRV systems can recover up to 90% of the heat/cool from outgoing air and transfer it to incoming air.
Apart from avoiding the dilemma of fresh air vs saving electricity on heating/cooling by keeping windows closed, an HRV is perfect for people who suffer from asthma as most of the pollens in the outside air can be filtered out within the system. It also lowers the risk of condensation, meaning a healthier indoor environment.
HRVs use no more electricity, and make no more noise, than a fridge – a small price to pay for constant fresh air inside and a stable comfortable indoor temperature all year ‘round.
Dispelling Some Myths about Passive Houses
We’ve heard some misinformation about Passive Houses (perhaps you have too). So we’d like to address some of the myths –
Myth 1: Passive Houses only work in Germany or cold climates. This is false. A Passive House will provide a stable and healthy indoor environment whether you live in a cold or warm climate.
Myth 2: You can’t open your windows in a Passive House. This is false. Of course you can open your windows. While the windows are open, the HRV system will not be able to maintain a stable indoor temperature, but when you shut the windows, the indoor temperature will stabilise again and the Passive House will continue to function as normal.
Myth 3: You can’t have a wood, gas or coal fire in a Passive House. It’s likely that you will not be able to have an open fireplace, but you can install fires that have a ‘real flame’ effect eg bio-ethanol fires.
Myth 4: When you go on holiday, you have to turn the HRV system off and so the house gets very stuffy. This is false. If you go on holiday, you can leave the HRV running. It will use no more electricity than your fridge.
Myth 5: Passive houses are very expensive to build. This is not necessarily true. If you are planning to build a good quality energy efficient home, lifting it to a Passive House standard will not cost significantly more. The glazing will be slightly more expensive, creating the air tight layers adds marginally to the labour and there will be extra insulation – however, these will not add significantly to build costs. Removing thermal bridges can be achieved through careful design, and doing this will not cost much more than a standard well-built home. The HRV system can actually be cheaper than a heating and cooling system.
Why Build a Passive House?
The top reasons to build a Passive House or incorporate Passive House principles into your renovation are:
1: Save money
Are you sick of budget busting electricity bills? Because Passive Houses only require a small amount of electricity to run, they are cheap to run. No need to fear your electricity bills or worry about increasing electricity prices.
The design and size of a passive house determines how much energy will be needed to heat and cool it. This means that it is possible to calculate how much electricity will be needed to heat and cool the passive house for its entire life span. A calculation to take to the bank when requesting a loan?
2: Fresh filtered air without opening your windows (and losing heat/cool)
This is an attractive proposition for most (if not everyone!), but is particularly crucial for those suffering from asthma or other respiratory issues where clean air is essential.
3: Reduce your carbon footprint
Less energy used means fewer carbon emissions generated. Passive Houses allow for energy savings of up to 90% compared with typical existing buildings.
If you’re interested in investigating the possibility of building a new Passive House or incorporating Passive House principles into your renovation, contact us! Building a passive house requires careful planning and execution, and it is essential that you involve appropriately certified professionals. Jeremy Gates, our Managing Director and Registered Builder, is a certified Passive House Tradesperson and is passionate about the benefits that Passive Houses have to offer.
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