Passive House: What Is It? How Much Can You Save?

How to save energy and achieve optimal thermal comfort with sustainable materials, thermal insulation, and ideal exposure.

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By Max Bender

passive house

The passive house is currently the most energy-efficient housing model. It is a concept developed in Europe and represents one of the most valuable contributions that university research has made in order to encourage sustainable construction.

What is a Passive House, Exactly?

Also known by its German name, Passivhaus, it is a construction that consumes very little energy and allows for significant economic savings.

It follows a specific building standard that maximizes the energy performance of heating and cooling systems while maintaining high living comfort, relying on intelligent design solutions, and renewable energy sources.

Origin of the Passive House

But let’s first delve into some history. The concept of the passive house emerged about thirty years ago, and it has an interesting story.

In the year 1988, two Northern European universities decided to collaborate to conceive a new generation of homes. The initial idea was to leverage the quality of construction materials and solar exposure to minimize the energy requirement for internal heating of the building. The protagonists of this collaboration were the German physicist Wolfgang Feist and Bo Adamson, a researcher at the Faculty of Engineering at Lund University in Sweden.

The result of the collaboration was surprising: it was discovered that by coordinating various devices and measures for thermal insulation and energy efficiency, buildings could be created that almost did not need heating, even in winter and in the cold climates of northern Europe.

The devices used were not new:

  • Wall insulation
  • Thermal windows
  • Building orientation for the best solar exposure
  • Ventilation system to recover heat during the necessary air circulation between the interior and exterior

However, by coordinating these devices in a reasoned manner and maximizing the quality level of construction materials, buildings were achieved whose energy efficiency was far superior not only to traditional buildings but also to those designed according to the latest thermal regulations.

Since then, passive houses have spread, first in the countries of Northern and Central Europe—Germany, Sweden, Austria, the Netherlands, Switzerland, France. Buildings based on the concept of the passive house have recently been constructed in the United States as well.

Let’s now look at some fundamental aspects of this type of housing and what interventions can be made to make the house sustainable.

How a Passive House Works

From a technical point of view, the efficiency of a passive house is due to the combination of several essential measures: thermal insulation, internal heat, thermal windows, shape and exposure, and ventilation. Let’s take a closer look.

  1. Thermal insulation: Achieved by increasing the thickness of the insulation material (about 30 cm compared to the 8-10 cm of traditional houses) and placing external thermal insulation, i.e., insulating material sheets on the outermost part of the wall, rather than on the inside as is normally done. The insulation covers all external walls of the building in their entirety, not neglecting the proper insulation of the roof.
  2. Internal heat: Thanks to perfect thermal insulation, the building can be heated by heat sources found in all homes but usually go unnoticed. These include active appliances, domestic lighting, sunlight entering through windows, the kitchen, hot water flowing in the bathroom, and the occupants themselves. Although minimal, the amount of heat produced by these sources is by no means negligible when adequately preserved.
  3. Thermal windows: A weak point in building insulation is generally the windows. In a passive house, the glass in the windows is triple instead of double. The glazed surface becomes more insulating than the frame itself, which is why designers tend to plan fewer large windows instead of many small ones. Large windows increase brightness and the heat produced by sunlight. At the same time, they reduce heat loss through the window structure.
  4. Shape and exposure: Thermal insulation is also achieved through the study of the building’s shape. Compact volume buildings better retain heat compared to fragmented or distributed volume buildings. It is necessary to plan the correct exposure of the building to the sun. In this way, the sunnier walls will be able to absorb heat, for example, through glazed surfaces. The colder and less sunny walls will instead be perfectly insulated. In temperate climates, shading of walls facing the sun must also be provided to keep the house cool in the summer months.
  5. Ventilation: Air circulation between the interior and exterior is necessary in all buildings but generally causes significant heat loss. In a passive house, the problem is bypassed through mechanically controlled ventilation. What does this mean? It is a system that, through a high-energy efficiency motor and a special heat exchange device, allows the incoming air to absorb up to 80-90% of the heat from the outgoing air before circulating indoors. This form of mechanical ventilation also serves to equalize the temperature of the different rooms in the building. It recovers heat from rooms where more is produced (such as the bathroom, kitchen, and more crowded areas) to give it to colder rooms, such as bedrooms and the living room. At the same time, it allows for the exchange of stale air.
passive house
A lovely example of passive house.

What a Passive House Must Have

A passive house, to be defined as such, should be designed to ensure high living comfort by minimizing the need for active heating and cooling systems.

Good efficiency can be achieved through thoughtful architectural design and intelligent building design, taking into account orientation, shading systems, natural sunlight, excellent insulation, intelligent heat management, and the use of renewable energy.

The building’s orientation should be optimized during the design phase. Good exposure ensures excellent natural lighting, reducing the need for artificial lighting and heating. The positioning of openings and the percentage of glazed surfaces also help capture and retain heat. Good orientation and the right amount of glass walls keep the house warm in winter, cool in summer, and well-lit. Adequate natural ventilation through the proper placement of windows limits the use of summer air conditioning systems.

Externally, natural or artificial shading systems such as awnings, sunshades, trees, green roofs, or other architectural elements designed to block the summer sun and reduce overheating are ideal for limiting the use of heating and cooling systems in different seasons.

Insulation leads to effective thermal insulation, which should be applied to the entire external envelope of the building with an external thermal coat covering walls, roof, basements, and floors. An insulating layer should limit heat loss in winter and coolness in summer.

Minimizing thermal bridges is a key element of these green homes. These are areas of construction where heat transfer to the outside occurs more easily (joints between masonry and fixtures, material changes for walls, joints between the load-bearing structure and infill walls), but they can be reduced as much as possible to avoid heat losses.

The presence of high-efficiency windows with double or triple glazing, filled with inert gas and well-insulated frames, is another key element to insulate the house from the cold.

Intelligent heat management involves using high-efficiency equipment and appliances, as well as lighting systems that consume less energy.

The use of renewable energy to meet the energy needs of the house, such as a solar thermal system for heating water or geothermal energy, the use of photovoltaic panels to produce energy, or other forms of renewables, allows for energy production and reduces dependence on fossil fuels, leading to savings.

The Importance of Design and Materials

Based on these essential points, different projects can include specific solutions and additional details, both aesthetic and functional. Some houses, for example, utilize geothermal energy, the natural heat of the earth, through pipes buried in the garden or courtyard that branch into the building.

In some cases, the study of solar exposure is combined with the use of modern photovoltaic technologies. Shading can be achieved with architectural elements or through the planting of suitable plant species. An example in this regard is deciduous plants: they lose their foliage in winter, allowing sunlight to pass when needed the most.

As for materials, the possibilities are wide-ranging: a passive house can be made of wood, bricks, or concrete.

The significant advantages of a passive house are evident: first and foremost, a significantly reduced ecological impact, thanks to the elimination or minimal use of the heating system, and secondly, comfort, thanks to optimal lighting and a uniform temperature in different interior spaces.

Benefits of a Passive House

The benefits for those who choose to live in an efficient house are evident, especially in the long term, considering the expenses for the design phase and materials that may seem higher initially. Furthermore, the savings for high living comfort are coupled with the value that the building maintains over time, making it more attractive on the market when put up for sale.

Let’s detail the advantages it offers:

  1. Greater Thermal Comfort: A more stable internal temperature throughout the year, achieved through effective insulation and airtightness, eliminating cold drafts and air currents.
  2. Good Indoor Air Quality: Thanks to a controlled mechanical ventilation system, a constant supply of filtered fresh air is guaranteed, reducing humidity problems, mold formation, and indoor air pollutants.
  3. Energy Savings: Lower energy consumption, up to 90% less energy used for heating and cooling compared to traditional buildings. This leads to substantial savings on utility bills. With the installation of renewable energy production systems, such as solar panels, energy self-sufficiency can even be achieved.
  4. Less Dependence on Energy Fluctuations: Lower spending on energy comfort makes the family less vulnerable to price fluctuations related to the volatility of the electricity market.
  5. High-Quality Materials: The standards required for a passive house involve higher-quality construction techniques and materials, resulting in a longer lifespan for the building.
  6. Higher and Stable Real Estate Value: The market value is always higher than that of a traditional building, thanks to the long-term energy and economic savings, appreciated by potential buyers.
  7. Improved Sound Insulation: Thermal insulation and airtightness also result in better sound insulation, reducing external noise.
  8. More Ecological Materials and Lower Environmental Impact: Sustainable materials used to increase insulation are also more environmentally friendly, reducing CO2 emissions because less energy is used for heating and cooling, and renewable energy sources are utilized.

Costs of a Passive House

The underlying idea is that a 100-square-meter passive house can be heated with only 100/150 dollars per year.

However, there are some problems, summarized in two fundamental elements.

Firstly, the cost, and secondly, the climate. The cost of a passive house is still relatively high. Even considering the expected savings in terms of electricity and gas bills, the initial investment can only be amortized over a relatively long period.

The cost is due to the high quality of materials, the high specialization of the reference professionals, and the need to use cutting-edge technologies.

passive house

The second problem encountered is common to all countries in the temperate zone: the passive house was conceived for the cold climates of continental Europe. Therefore, the simple transposition of the original model may not be the best choice when building in countries with warmes climates. In many regions, summer sun and heat pose a much greater problem than the rigors of winter, and this must be taken into account during the design phase.

In several countries, designing a passive house can cost even twice as much as a regular construction or renovation. The cost can vary from 3000 to 5000 dollars per square meter, making it a (average) higher expense compared to traditional construction.

However, a calculation of the real costs cannot be made, given the numerous variables involved. The results always show an average energy saving of 90% and an increase in the home’s value.

That being said, and with all the eventualities of specific cases, with a passive house, savings in the long run do exist. It has been calculated that a passive house needs an average of 1.5 liters of fuel (equivalent to about 15 kWh) per square meter of living space, compared to the 10-12 liters consumed by a traditional house solely for heating. This represents a 90% saving!

Where Passive Houses Are Found

A house is considered passive if designed following well-defined standards established by the Passivhaus Institut in Darmstadt, Germany. The goal is to reduce the energy demand for heating and cooling to a level that can be easily offset by renewable sources, leading to an almost zero or very low energy balance.

Buildings that meet these criteria are increasingly found. Obviously, these are almost always newly built single-family homes because the criteria for making them low-impact are defined during the design phase. This is not easy with the renovation of an existing building, especially since orientation and shading are elements defined by the original design and not replicable during renovation.

In Europe, especially in Northern countries, outside larger urban centers with historical or 70s-80s buildings, there are several houses built with these new criteria because they are designed from scratch and are single-family homes. However, numerous multi-family and public buildings are also constructed with these criteria.

How to Certify a Passive House

You need to check if there is an affiliate institution in your country connected to the Passivhaus Institut in Darmstadt to submit the certification request with all the necessary documents, photos, and anything else needed to indicate that the building is equipped with efficient systems. It must also include:

  • Passing the blower door test for the airtightness of the building elements
  • Project documents related to systems and structures
  • PHPP software documents
  • Declaration from the works director certifying the correct execution of the works based on the PHPP software
  • Passing of 3 tests: airtightness < 0.6 h-1, primary energy requirement < 120 kWh/m2 per year, energy demand < 15 kWh/m2.

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