The passive house

From the German term “passivhaus”, the passive house is the most sustainable housing model currently in the design scenario.

Its origins date back to the 80s and 90s of the 900th century, when two Northern European scholars and physicists started some studies with the aim of identifying the construction standards aimed at creating buildings with low environmental impact. The result allowed to achieve excellent performances for energy saving but rather high manufacturing costs that did not make the proposal applicable by a large user base.

However, since it was a typology that guaranteed many advantages in terms of energy and comfort, studies continued and the model developed to the present day as an excellent example of sustainable construction.

Although it is an innovative proposal in the construction field, the passive house uses already known technologies and its real novelty consists in the particular combination of these solutions. In fact, ecological construction materials are used, the orientation and solar exposure are exploited and the compact physical shape and very large openings are preferred. In fact, thanks to the correct thermal insulation, the containment of energy consumption and the use of passive devices, this type of building requires little auxiliary energy for its heating. It follows that the traditional systems used in homes such as boilers and water heaters that involve the use of a lot of energy are not necessary.

Built with a wide range of materials (wood, concrete, brick), passive houses can be considered almost self-sufficient and guarantee high quality standards. Initially, they were widespread in Northern Europe (Germany, Sweden, Switzerland, France) and only later did they also spark the interest of designers in the Mediterranean area.

However, it is important to specify that it is not possible to apply the model indiscriminately in geographical areas with different climatic characteristics, but it is necessary to shape the design choices on the specificities of the place. For this reason, in Italy there is a growing interest in this type of construction but the necessary studies for the application of the model in temperate climates are underway.

As time goes by, such building schemes will prove indispensable to safeguard the environment and future generations. To understand the importance of sustainability applied in construction, we must be aware of how destructive the use of non-renewable energy sources is in the long term. Furthermore, as far as the Italian scenario is concerned, the economic boom of the 50s and 60s of the twentieth century caused uncontrolled construction aimed at high profit at the expense of quality in terms of energy and comfort. For this reason, today it is good to remedy this situation and adopt, in the design stage, some measures considered indispensable: the optimization of resources, the exploitation of renewable sources, the containment of energy consumption and the adoption of passive systems as the only solution for heating. These choices are used in the passivhaus which, in addition to having a minimal ecological impact on the ecosystem, ensures high living comfort at reduced management costs.

Features

Once the concept of passive house has been clarified, it is necessary to illustrate the technological choices that distinguish it and make it an optimal model for sustainable architecture. As anticipated, the typological scheme combines together reasoned design solutions, placing particular attention on respect for the environment and its protection.

PHYSICAL CONFORMATION AND ORIENTATION

The first aspect to consider concerns the shape of the building: a compact volume is preferable to discontinuous and irregular elements. In fact, the presence of protruding and overlapping bodies causes the formation of harmful thermal bridges, origin of huge heat losses. It has been demonstrated that, on the other hand, structures with regular and linear lines are able to optimize the energy needs of the entire system, retaining the heat incident on the facade better and for longer. The position of the building is also very important if we consider the peculiarities of the place where it will be inserted. In fact, it is necessary to consider some climatic and local phenomena that will necessarily affect the success of the project. In order to choose the optimal orientation for a building, it is necessary to calculate its position in relation to the cardinal axes, the shading deriving from pre-existing buildings, the presence of wind currents and sources of noise.

As for the first aspect, today the east-west axis is preferred with the aim of making the most of the hours of sunshine on the southern front during the winter. In fact, as is well known, solar radiation varies depending on the season of the year and for this reason it is good to opt for improved solutions compared to the least favorable period. Furthermore, the sunshine conditions vary greatly depending on where you are: in colder countries it is preferable to make the most of solar radiation, while in dry and arid places it is necessary to maximize fresh air currents. These measures are used in order to improve the thermal comfort of internal environments by exploiting local climatic characteristics.

Shading is also an element to take into consideration since it is good to consider how the quantity and quality of the sun's rays that hit the facade vary in relation to the presence of buildings or screening elements in the immediate vicinity of the building in question. Otherwise, this phenomenon can be indispensable in particularly arid and muggy territories. In order to mitigate excessively hot climates, ventilation currents also intervene, which are very useful for buildings with an east-west orientation. In this case, the warm winds coming from the south will balance the cold winds present on the north front.

INTERNAL FUNCTIONALIZATION

In order to maximize solar orientation, the choice of the intended use of each individual internal space must be undertaken taking into account the solar trend. Given that in the case of residential buildings, an east-west orientation is preferable, it is best to allocate the rooms facing south to the living area (living room/kitchen/study) and place the sleeping area and accessory rooms (bathrooms/storage rooms) on the north side. In fact, the south side is considered optimal because during the cold seasons a greater quantity of solar rays hits it, thus enjoying more heat, while in summer the highest sun hits the rooms more indirectly without overheating them. If the apartment enjoys an east view, it is advisable to place the bedrooms there, so that they can enjoy the first heat of the morning and will not become excessively hot in summer because they are in the shade in the afternoon. The rooms on the west side, on the other hand, receive solar rays throughout the afternoon, and in summer require screening elements to alleviate excessive heating.

THERMAL INSULATION

In new generation buildings, designed according to the Passivhaus standards, the perimeter walls and floors are equipped with a very thick layer of insulating material (30 cm), usually positioned inside the outermost section of the wall. This particular insulation also concerns the roof of the house, since it constitutes an integral part of the building in direct contact with external atmospheric agents.

If you want to improve the performance of the envelope of a pre-existing building, you will need to intervene by inserting a coat that can be external or internal. The first type is usually used in detached houses, while the second is chosen in the case of intervention on individual units belonging to larger buildings (urban condominiums). In this way, the perimeter walls ensure low transmittance and high thermal insulation, so that in winter the heat necessary for heating the environment is retained and in summer it is blocked outside. Thanks to this measure, it is possible to enjoy optimal living comfort during all seasons of the year.

PASSIVE HEATING SYSTEM

The adequate thermal insulation that characterizes the passive house allows it not to require traditional heating systems. Heat sources that are too often underestimated contribute in part to ensuring balanced temperatures: household appliances, lighting fixtures, kitchen stoves, occupants of the house. Furthermore, sustainable solutions such as solar panels and heat pumps are used; the former produce thermal energy by exploiting incident solar rays, while the latter contributes to the same function by using resources such as air, water or soil. These are alternative methods to the systems used in the past that required a large expenditure of non-renewable sources and a significant production of pollution harmful to the fate of the planet.

HIGH PERFORMANCE FIXTURES

They have always been the connecting element between the inside and outside of the building and for this reason, in traditional homes they can often represent a danger for drafts and heat dispersion. In order to avoid this type of inconvenience, the passive house uses only triple glazing, which, since it is extremely insulating, guarantees air, water and cold sealing. Furthermore, a few large openings are preferable, which allow more sun rays to filter into the internal environments, thus providing them with a greater quantity of heat and lighting. This benefit is maintained inside the building, thanks to the high capacity of triple glazing to thermally insulate. It is therefore preferable to choose windows with frames that perform on average but are insulated to the maximum, up to the glass edge, so as to obtain high performance guaranteed through a preventive calculation.

CONTROLLED VENTILATION

In order to ensure appropriate hygienic and sanitary conditions inside living spaces, it is well known that adequate internal air exchange is necessary. However, especially during the winter season, opening windows can cause excessive heat dispersion. To address this problem, the passivhaus model proposes the inclusion of a ventilation control system. This system consists of a device designed to monitor heat exchange and can work for both cooling and heating. In fact, this system allows the incoming cold air to retain the heat of the outgoing flow from the service areas (bathrooms and kitchen). In this way, an air exchange mechanism is triggered between excessively heated rooms and colder rooms (perhaps positioned on the north side of the building), so as to ensure optimal and more balanced comfort between the various rooms.

It is therefore possible to note how all the phenomena analyzed contribute to making a passive house more or less efficient: the thermal insulation of the perimeter walls and controlled ventilation each have an impact of 30%, the type of window and the presence or absence of thermal bridges contribute to the total with 15% and finally the orientation and presence of electrical appliances with 15% each. These standards belong to the passivhaus model that was introduced and tested in territories belonging to Northern Europe, characterized by rigid climates and low temperatures.

In order to apply the same scheme in the Mediterranean area, which is characterized by its mild climate in winter and hot in summer, it is necessary to assume that the standards must be shaped on the particularities of the place. If in the first case the primary need is to heat the interior spaces of buildings, in Southern Europe the need is the opposite, since there is a greater need to cool the spaces during the summer season.

To overcome this situation, a study was conducted on the specific territorial features that allows the model to be applied paying attention to the cooling aspect. In fact, if the dictates of the passivhaus model, conceived for the most rigid climates, can also be applied in more temperate areas, it is also true that in such territories it is also necessary to prepare adequate systems of darkening from the sun's rays (essential during the day) and low-consumption cooling systems. These are extremely important measures especially if applied in highly urbanized contexts, where heat islands and concreting contribute significantly to environmental overheating.

Advantages and disadvantages of the passive house

The model described involves a series of positive and improving aspects for the quality of life but, as with all choices, it also presupposes some disadvantages. As anticipated, it is the most sustainable current building typology of all; in fact, thanks to the application of pre-established building standards it is possible to obtain significant savings in terms of energy and money. In fact, energy consumption compared to a traditional building is reduced by 90% and management costs are significantly reduced.

These results are achieved through the use of solutions designed to increase thermal insulation, exploit local environmental resources, control ventilation and eliminate thermal bridges. Passivhaus are considered ecological and efficient because they exploit natural resources without compromising the well-being of future generations and require low management costs.

Furthermore, a greater psychophysical well-being is found in the occupant, since the air quality is better and the environment is healthier and safer. Despite obtaining such a positive balance, the passive house model also involves some disadvantages. The first concerns the initial investment cost which is higher than usual and amortizable over a fairly long period of time. However, prices can vary depending on the needs imposed by the specific location and the higher cost is due to the higher quality of the materials used. Unfortunately, currently, on the Italian territory the model has not yet spread on a large scale both because of the need to adapt the Nordic model to the temperate climate and because the costs are still too unpopular. However, the growing awareness of the importance of the diffusion of low environmental impact buildings, pushes us to hope for a concrete improvement also at a national level.

The comparison between a traditional building and a zero impact one

The passive house is distinguished from all other housing models by its intrinsic characteristics and by how these elements are all grouped together in the same project. Naturally, the needs and performance of a passivhaus vary depending on the location where they are located, because as already mentioned, the same building will have different consumption depending on the local climate and the needs aimed at obtaining internal thermal comfort.

A recent study calculated the CES, or specific energy consumption, of four building typologies that hypothetically had the same characteristics in terms of square meters, typology, floors above ground and location. The comparison was made between an old building, a building constructed according to the law that imposes the containment of energy consumption, a low-consumption house and a passive house. The energy balance of each typology was calculated in one year: the first building would consume 5500 liters of diesel for heating, with losses due to dispersion and transmission equal to 913 liters and gains equal to 550 liters.

The CES would correspond to 37 liters. Through the measures provided by law 10 of 1991, the same building would guarantee lower losses with a diesel consumption of 2.200 liters and a CES of almost 15 liters, thus more than halved. This is the case of the most common residences currently. Then there are low-consumption buildings that, through the optimization of thermal insulation and the use of adequate windows, significantly reduce dispersion, guaranteeing a CES of less than 7 liters. Finally, the most sustainable model is represented by the passive house which, thanks to the absence of thermal bridges, the compact shape, the correct orientation and the use of low-consumption systems, guarantees a CES of less than 1,5 liters.

Summarizing the results obtained from the study in the table:

BUILDING TYPE	*CES (lt)
Old building	37
Building according to Lex 10	15
Low energy house	<7
Passive house	<1,5

Since the difference between the consumption of an old building and that of a passive house is very significant, there is a growing interest worldwide in making significant improvements to the built environment to bring it as close as possible to optimal standards. In fact, through careful renovation it is possible to improve the energy efficiency of even the oldest buildings.

First of all, it is necessary to carry out an energy diagnosis of the building to identify the weak points on which to intervene to achieve greater well-being and an optimal cost-benefit ratio. One of the first elements that must be analyzed is the envelope: an intervention to thicken the insulating layer could lead to a clear economic saving. In fact, in this way the internal environments would require a smaller amount of energy necessary for their heating.

In these cases, it is possible to intervene with a thermal coat that can be applied to the external or internal layer of the perimeter walls. In the first case, the insulating power is greater and the operation does not compromise the internal usable square footage, but the costs are higher and intervention is made from the outside only if the entire condominium requires this type of solution. Instead, when you want to proceed with this action on the single housing unit, you need to opt for the internal coat that is easier to install and can be chosen in numerous variants of insulating material (wool, expanded polystyrene, wood fiber, cork, mineral foams).

Another fundamental aspect is represented by the controlled mechanical ventilation which, thanks to a heat recovery system, guarantees the exchange of air without causing useless dispersions. This solution, combined with the others, guarantees the cessation of the use of fossil fuels and the exploitation of renewable sources present in nature.

Sometimes, installing a photovoltaic system on the south-facing roof slope allows you to exploit the sun's rays to produce energy useful for the home's energy needs. It is also a good idea to check the condition of the window frames and replace them with high-performance products. These interventions allow you to significantly improve the condition of the building and make it go from a very low energy class (G) to an ideal class (A), optimizing performance and ensuring greater comfort in the interior spaces.

However, it is important to specify how the decision to improve the characteristics of an existing building is more difficult in the case of large buildings. This is because the presence of many housing units presupposes the agreement of a large number of people, often inattentive and disinterested in important issues such as environmental protection. Fortunately, the current scenario sees a growing awareness of the problems related to pollution and the possible solutions that concern more sustainable construction, thanks to which, in exchange for greater expenditure, economic savings are guaranteed while respecting the environment.

Realized examples

The origin of the passivhaus lies in the northern European territories and only later did the model spread to the central European area. The first example built, in 1991, is located in Germany and consists of a group of four independent villas; subsequently, in 1999 the first multi-family complex was built in Freiburg.

Over the years, there have been various types of residential constructions that have affected Sweden, Germany, France, Switzerland and Austria. It is precisely this last nation that has seen the passive house establish itself as a standard model established by law and in some areas today, it is a mandatory choice for new constructions. Late compared to the European scenario, America has established itself, where in the USA the passive house arrives in 2006, thanks to a German program.

In all cases, the model is successful thanks to the attention to detail, the sensitivity in the use of quality materials and the maintenance of high living standards. As regards the Italian situation, in recent decades there has been a growing interest in issues concerning the containment of energy consumption and the efficiency of buildings.

The diffusion of the passive house is still slow and differs greatly between the northern area of ​​Italy and that of the center and south, in fact, the passive buildings built are mostly in Trentino Alto Adige. Furthermore, the CasaClima agency is based in Bolzano, an organization that deals with the study of the performance of buildings located in the regional and national territory. The organization has established a law that provides for mandatory energy certification at provincial level and a protocol with reference standards according to which a building with Casa Clima Oro classification has the characteristics of a passive house. This last typology still concerns a low percentage of the Italian built fabric, in fact only 80 buildings have been certified. However, Italy ranks fifth in Europe after Germany, Austria, Switzerland and Belgium.

Let's now see how the passive house standards are implemented in different building typologies:

PUBLIC BUILDING
Ex-Post Bolzano, Michael Tribus Architecture, 2004

Through the recovery of the old building intended for the Bolzano post office, dated 1954, the new headquarters of the Province was established, which today represents the first example of a public passive building. The original compact shape and the reduced presence of openings have allowed the requalification of the pre-existing building into a passive house.

From the point of view of the envelope, the walls, previously made of bricks without insulation, have been equipped with an external coat consisting of a 35 cm thick insulating layer, while all the windows have been equipped with triple glazing. Furthermore, on the façade, it is possible to observe the particularity that characterizes the envelope in correspondence with the openings: the oblique and changeable intrados maximizes the exploitation of the incident solar rays. In this way, the energy needs of the building and its thermal insulation have been optimized.

As regards the distribution of the internal spaces, the old plan was characterized by a subdivision into spaces diversified according to the function. During the design phase, a complete redefinition of the spaces was carried out, which today includes a central corridor and two lateral sections occupied by the new offices. The project also included the renovation of the plant system, through the replacement of the old boiler with an air conditioning system that provides heat recovery and that consumes only one liter of fuel oil, per square meter per year, used for heating.

Finally, a roof garden has been set up on the roof to help cool the building in the summer. The ExPost in Bolzano is now the first Italian example of a zero-impact building, which, thanks to targeted interventions, has reduced consumption for its management and use by 90%.

PRIVATE HOUSE-STUDIO
Passive House Studio House, Piraccini+Potente Architecture, 2018, Cesena

Another virtuous example in Italy is represented by the Casa Studio Passive House in Cesena, which is a renovation and remodeling of an existing urban complex, in a sustainable way. The original building is converted into a residence and professional studio and through the use of particular technologies, it reduces costs and energy consumption in full respect of the environment.

The use of different materials ensures the exploitation of their natural properties and makes the building highly efficient. The intervention involved the use of a high-performance casing that, thanks to the optimized insulation, allows the rooms to be heated without resorting to traditional heating systems. In fact, the heat is provided by passive systems, such as solar rays, household appliances and the occupants of the house.

Furthermore, thanks to the controlled ventilation system, the heat of the air coming out of the domestic environments is retained and reused in the incoming flow of filtered air. These measures make the building respectful of the environment (reduction of pollutants), energy efficient and a guarantee of the psychophysical well-being of those who live and work there.

Interior front of the residence and office – Photo: Daniele Domenicali from archello 

SOCIAL HOUSING
11 Logements collectifs, VOUS ÊTES ICI ARCHITECTES, Paris, 2014

This is an innovative example of a passive building applied to the social housing building typology. The project, located in a central area of ​​Paris, in the V Arrondissement, is carried out with particular attention to the pre-existing and includes residences and services.

The complex is characterized by a compact shape and alternating full and empty spaces, while the facade is characterized by a laminated skin in treated wood. The openings are equipped with double glazing and flexible shading elements that give the possibility of regulating the level of natural lighting and heating according to needs. The correct thermal insulation, the high-performance double glazing, the presence of solar panels and a roof garden, together with the loggia system facing south, guarantee the high efficiency of the buildings that compose it.

The latter are characterized by individual apartments of different sizes that enjoy a particular orientation, designed to maximize the exploitation of the sun and wind currents and therefore ensure adequate thermal comfort. This project constitutes an innovative example for the typology of social housing and stands out for the typical peculiarities of the passivhaus and for the balance with which it fits into the pre-existing urban fabric.

Overlapping blocks and detail of the laminated wooden facade with holes – Photo: Architizer 

UNIVERSITY LABORATORIES
Warren Woods Ecological Field Station, Go Logic, Michigan, 2006

This is the first passive research center that houses the laboratories of the University of Chicago. The area is characterized by the pristine reserve that rises near the shores of Lake Michigan and the building, with high performance, fits harmoniously into the context.

The aim of the project was to create a University branch for research that was highly sustainable from an environmental and economic point of view. The compact shape of the building and the linear design were chosen precisely to maximize the thermo-hygrometric performance.

Differently from a passive residential building, in this case it was necessary to ensure humid environments, useful for analysis and experiments, but at the same time comfortable spaces for the occupants. To this end, in the plan, all the laboratories were placed on the north side, less exposed to the sun's rays and therefore less heated, while the rooms intended for meetings and training are exposed to the south. The large openings are equipped with glass to control the sun's rays, so as to guarantee the entry of light but at the same time avoid overheating.

In this regard, traditional heating systems are excluded in favor of a solution, specifically designed for the case in question, capable of exploiting the heat produced by the laboratory machinery to heat the internal environments. Furthermore, it is important to specify how the highly insulating envelope helps to avoid unnecessary heat dispersion. From the point of view of materials, wood was chosen for the facade in line with the natural context and steel for the solar screens.

Facade of the building and detail of the perforated metal blackout panels – Photo: www.inhabitat.com

The construction of passive buildings is essential for the well-being of today and of future generations: energy efficiency, saving of available resources, careful choice of technologies and materials, attention to detail and respect for the environment must always be the basis of quality architectural design.

The legislation

The current scenario presents us with problems regarding the building-environment relationship and the consequences that a design lacking awareness and responsibility for future generations would entail.

It is important that a model that can improve the quality of life, while fully respecting the planet, is conceived right away. For this reason, the European Union programs are committed to regulating new construction as much as possible so that it guarantees energy savings and the reduction of pollution produced. In fact, it is well known that urban buildings are highly energy-hungry and cause 50% of global energy expenditure. Studies and research have shown that a "typical" European house is responsible for high consumption (29% of total electricity) and ever-increasing management costs.

It is therefore clear that this situation must be remedied by intervening at a comprehensive level, in order to reduce waste and maximize the energy performance of the built environment, exploiting renewable resources. To this end, the EU Directive 31/2010 of the European Community was established, which established that starting from 2018 all public buildings and from 2020 private ones, must comply with specific standards in order to make them almost passive buildings, that is, with reduced energy consumption (almost zero).

All countries that are part of the European Union establish minimum standards that must be respected in the perspective of a forward-looking construction. Starting from the peculiarities of the place where the building is located, it is essential to improve its performance, minimizing its energy consumption. To operate to this end, it is necessary to intervene on the pre-existing through the insertion of specific technologies and systems and foresee them without hesitation in the new construction.

The air conditioning systems of the rooms, those designed for hot water and lighting systems, must comply with the requirements aimed at energy saving. These requirements are verified through certificates, valid at European level, which attest the energy class of a building and its characteristics. As regards the certificates relating to passive houses, few buildings have earned this certification to date. These are properties that enjoy low consumption during the year (120 kWh/mXNUMX) and are characterized by very high levels of thermal insulation and optimal energy efficiency. In Italy, studies and research are still underway for the analysis of the built environment, necessary to develop an action plan aimed at optimizing the overall performance from an energy, economic and social point of view.