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If you are planning a new build or just curious about ways to save energy on your heating bills, you might have heard of the passive house concept. For those who do not know, passive houses are highly energy-efficient buildings that can consume up to 90% less energy than regular housing.
The basic principles of passive house are fairly simple and can be condensed down to just a few key points. These are as defined by the International Passive House Institute.
- Buildings should have quality continuous insulation.
- Buildings should be airtight with no gaps or leaks to allow escape of heat or entry of drafts.
- Buildings should have high-performing windows and doors, either double or triple glazed, depending on the climate.
- Buildings should use mechanical ventilation to maintain a healthy and comfortable internal atmosphere. The heat and moisture recovery as part of the system should be utilized for efficiency.
- Buildings should not have thermal bridging. This means they should not contain components that conduct heat from inside to outside the building.
It is worth noting that the passive house concept is not the product of one person, but rather a point arrived at after contributions by numerous individuals and institutions. Many of the core ideas are just common sense.
Our buildings should not needlessly waste energy when smarter design can overcome this issue. It does not seem like such a radical idea. In fact, should it not be the standard for all new buildings?
Why passive house is necessary
According to research published last year by PNAS, housing accounts for 20% of the annual greenhouse gas emissions of the United States. Redesigning housing to be more energy efficient is just one of the big steps we can take toward a more sustainable future.
If our houses and workplaces performed on average, a fairly conservative 60% better, this would reduce housing related greenhouse emissions to only 8%.
Switching to sustainable energy sources is a much more green alternative to power produced by fossil fuels. It is also a big commitment for the future. By building and retrofitting our houses to perform better, we can drastically reduce the amount of power we require in the first place. This makes sustainability a much more attainable goal.
A short history of passive house
What many people do not know is that passive house design is a somewhat international idea. Though the idea was more fully defined in Germany, its roots lie in North America. During the oil crisis of the mid-1970s, a team from the University of Illinois developed an energy efficient housing design they called the Lo-Cal House.
The Lo-Cal House design features double thick walls with offset studs to cancel out thermal bridging. Thermal bridging occurs when a construction material such as wood conducts heat from the inside of a building to the outside. Often this happens when an uninsulated stud or rafter makes contact with both inside and outside surfaces.
This can considerably lower the insulation properties of a wall, in some cases by 30% or more.
Eliminating thermal bridges and making use of additional layers of insulation can drastically reduce the amount of energy needed to heat a building.
In 1977, a team of engineers built what is known as the Saskatchewan Energy Conservation House. They took the Lo-Cal House design a little further with higher rated insulation. They also implemented a solar heating system and the house was one of the first to be fitted with an air to air heat recovery unit.
The concept was taken up in Germany by physicist Dr. Wolfgang Feist who refined it and defined passive house (Passivhaus) standards. He also founded the Passivhaus Institute in 1996. It is an industry leader in research and development of passive house construction concepts and materials, and a design resource.
Passive house for different climates
There is no one-size-fits-all design that would be suitable for every climate. In colder climates, houses would naturally want to take advantage of direct heating from the sun. This requires south facing windows to allow in the sun’s heat during the daylight hours.
A house in a tropical climate would likely require a very different design. The insulation properties may be equally high, but the design would concentrate on decreasing the amount of heat transferred through roofs, walls and windows.
For those who wish to build in more moderate climates, lower amounts of insulation would be required.
Examples of passive houses, in such diverse climates as the US, Canada, Mexico, Spain, Taiwan, Greece and the United Arab Emirates, illustrate that there are many possible solutions to the challenges of different climates.
Retrofitting an existing house
The passive house standard is not just for new builds, but can also be applied to pre-existing buildings. This can be achieved by improving insulation, replacing windows with high quality units, increasing how air-tight the building is, adding ventilation with a heat recovery system, as well as using renewable energy sources like solar power.
Significant energy savings of between 75% and 90% have been achieved by applying the standards. However, it is not always possible with some buildings due to pre-existing structural thermal bridges. There is, therefore, a different standard for retrofitted buildings called EnerPHit.
Passive house in the United States
The term Passive house is being used more regularly and if a building is specified as such, it should be certified. Certification allows you to know that the building is achieving the highest possible performance standards.
It is not so much a necessary standard to comply with as a tool to aid construction. The certificate is helpful in letting you know where improvements can be made. It can also equip you with the knowledge you need to make your home as energy efficient as possible.
There are two agencies that are able to certify a building in the US. These are PHI (international Passive House Institute) and PHIUS (Passive House Institute US). The two companies were once affiliates, but have since parted ways, which means there are two differing certifications for passive house in the US now.
Though there are differences between the two, you will end up with a highly energy efficient house with either of the institutes you choose.