The passive house (originally named ‘PassivHaus‘ in German) is a house, or building, capable of covering most of its energy needs by harnessing solar contributions (for heating) and shading elements (for cooling). This, combined with mechanical ventilation systems with heat recovery, high-performance thermal windows, and proper thermal insulation of the envelope, results in extremely low consumption for maintaining the indoor temperature.
In recent years, especially since the energy crisis of the 1970s, there has been much talk of NZEB (Near Zero Energy Building) structures. These buildings require a minimal amount of energy, making them more “sustainable” from an energy standpoint, given the global energy crisis and related CO2 emissions into the atmosphere.
In 1988, thanks to the studies of Professors Feist and Adamson in Germany, the Passiv Haus system was born, aiming to enhance and optimise all the constructive components of the building envelope to reduce energy consumption, increase indoor comfort, and improve hygienic conditions.
In 1996, the Passivhaus Institut was established, an independent research institute in the field of building energy efficiency. This institution has made substantial contributions to the collection and processing of climatic data, building performance simulation, the development of high-performance building design software, validation and development of construction components, and knowledge dissemination (www.passivehouse.com).
A Passivhaus can save 90% of the energy for heating compared to ordinary buildings and about 75% compared to the legal requirements in Italy. Given the very low electricity consumption, the rising energy costs, which significantly increased in recent months due to energy dependence on other countries, do not pose a threat to Passive Houses.
A bit of story of Passive House
The first Passivhaus was built in Darmstadt, Germany, in 1990/91, and was the residence of Feist himself.
The building, which houses 4 families, has been continuously monitored over the years, consistently maintaining the same energy consumption. Despite a construction cost increased by 8% compared to the minimum requirements for terraced houses, the set objective was achieved, and the project was later presented at the 2000 Hannover expo. Since then, many PassivHaus projects have been implemented mainly in Germany, Austria, France, Switzerland, and Sweden.
Key Points of Passive House
It should be noted that Passivhaus is not a brand or construction standard but an open and publicly accessible system. They are general principles derived from physics, applied to building envelopes, to achieve high performance. Thus, the principles are applicable to any technology or construction system: masonry, wood, or others. A Passivhaus consumes (for both heating and cooling) a maximum of 15 kWh/m2 per year or 10 W peak consumption per net square meter of walkable surface.
Passivhaus buildings (Classic, Plus, Premium) can be certified by the Passivhaus Institut and to obtain this must follow specific design and execution procedures.
But what are the basic principles of a Passivhaus?
- BUILDING ENVELOPE (external insulation)
- THERMAL BRIDGES (reduction and/or elimination of thermal dispersions leading to molds and condensation)
- WINDOWS (use of high thermal performance external windows)
- AIR TIGHTNESS (significant reduction of air exchange between inside and outside)
- MECHANICAL VENTILATION (mechanical regulation of air exchange with heat recovery)
Thanks to the careful design of the above elements, it is possible to ensure:
a. Thermal comfort (adequate internal temperature)
b. Hygiene criteria (constant control of the air humidity level)
c. Energy savings (sustainability)
d. Economy (low building maintenance costs)
Passiv Haus Certification Criteria
What are the criteria required for a building to be certified Passivhaus? Let’s take the generic data provided directly by the Passivhaus Institute.
- The heating energy required must not exceed 15 kWh per square meter of net surface or 10W peak per square meter. The same applies to cooling, with a tolerance for air dehumidification.
- The primary renewable energy (PRE) used by all appliances must not exceed 60 kWh per square meter per year for Classic certification, 45 kWh/m2 per year for Plus, and 30 kWh/m2 x year for Premium certification.
- The air tightness (air exchanges between the inside and outside due to infiltrations), calculated with a pressure difference between the inside and outside of 50 Pa, must not exceed 0.60 per hour.
- The air heat recovery rate of the ventilation system must not be less than 75%, and the energy requirement for ventilation must not exceed 0.45 Wh/mc.
- Thermal comfort must meet the criterion that the living areas of the building should not overheat (internal temperature exceeding 25 degrees) for more than 10% of the solar hours in a year. Also, indoor air humidity cannot exceed 12g/kg except for 20% of the annual hours.
Advantages and costs of a Passive House
The main advantages associated with designing a passivhaus are related to physical well-being, hygienic comfort, and energy savings. It should be noted that the passivhaus system does not stem from the need for economic savings related to the cost of energy resources, but this aspect should not be underestimated.
Furthermore, it should be highlighted that the care required in constructing the envelope, which must meet high technical and constructive requirements, reflects the quality and therefore, greater building durability with a consequent reduction in interventions and maintenance costs. This is an aspect that should be seriously considered in the economic evaluation of a Passivhaus. Often, it is necessary to evaluate not only the initial investment, which can sometimes be higher, but the annual costs, considering energy savings, low maintenance, and high living comfort, over the entire life of the building.
From common experience, a passive house costs approximately 10% more than a traditional home. However, this figure needs to be analysed on a case-by-case basis. Passive house design considers various factors, from legal aspects to exposure, shape, number, and size of openings, to architectural features. Each of these elements can influence the final cost; for instance, proper exposure can maximise solar gains.
A special mention is deserved for the finishes, which, of course, impact the overall construction cost. Taking into account the above, this average additional 10% in costs can be offset, or at least reduced, by decreased energy expenditures over time, reduced maintenance needs, increased building longevity, and last but not least, an overall higher quality. This quality often translates into higher marketability of the building, even from an investment perspective (for builders and investors).
It’s always advisable to consult with a knowledgeable expert when planning your Passive House. The factors in play are numerous, and it is recommended to engage a team of professionals capable of achieving what is termed as the cost-optimum, meaning the best cost-benefit ratio in constructing a Passivhaus.
In conclusion, the Passivhaus represents a challenge and an opportunity. It is an invitation to shift our design perspective towards a future where comfort, health, and sustainability are perfectly balanced.
Bureau69 Architects is a PassivHaus supporter, and Massimiliano Strano is an architect who has undergone official PassivHaus Designer training. He can ensure the right professionalism and the correct network of collaborations among designers, technicians, certifiers, and installers to achieve your predetermined goal of constructing your PassivHaus. If you wish to discuss your project, please contact us by phone or fill out the form on our contact page.
For further insights, you can refer to the document at https://passivehouse-international.org/upload/PH_brochure_IT.pdf.
PHOTO: PASSIVHAUS INSTITUTE