What are passive houses and how do they work?

Passive houses are those that make the most of bioclimatic architecture to create a building with high energy efficiency whilst ensuring suitable comfort throughout the year for those who live there.

When was the idea of passive houses invented?

At the end of the 70s, people were already beginning to think about sustainable awareness. To this awareness we should add the oil crises of 1973 and 1979 which led people to start thinking about the energy model, especially in the United States.

American schools of architecture took these currents of thought into account and began to consider the idea of buildings that used as little energy as possible without economising on the comforts of the people living in them.

The result of these works was the publication of a book called "The passive house: Climate and Energy Saving" published in 1979 by The American Institute of Architects. This manual represents a commitment to taking advantage of the climatic particularity of the location of dwellings to increase the independence of traditional cooling and heating systems that are dependent on the conventional fossil fuel network.

This milestone opened a line of development for architecture in the following decades, making maximum use of technological innovations in design and construction.

What factors should be taken into account in passive houses?

Here are some determining factors when creating a passive house:

• The geographical location: Its position as well as its orientation establishes a specific climate, a house facing northeast does not enjoy the same advantages as one facing southeast.
• The prevailing climate: by consulting historical records and forecast models, you can learn about the hours of sunshine, the volume and frequency of rainfall, relative humidity, average, maximum and minimum temperatures, etc.
• What the house is used for: If it is a workspace, if it is a habitual residence, second residence, etc.
• The number of people who live there and their routines: It is important to know the use that will be made of the house, what spaces will be needed (office, games room, etc.), what they will be used for and when (morning, afternoon or night).
• The shape of the building and its relationship with the surrounding area.

These factors will determine what needs to be done to obtain minimum comfort (stable and pleasant temperature throughout the year, depending on the season) in spite of the climate, making use of the advantages of the climate and mitigating the disadvantages.

What resources do passive houses use?

Architects combine a series of resources depending on the characteristics of the house:

• Thermal insulation of the house and the materials used for this.
• Cross ventilation and protection against draughts.
• Capturing solar and/or wind energy. Taking into account the movements of the sun and prevailing winds.
• The thermal mass of the building, to maintain a stable temperature. The large majority of passive houses maintain an internal temperature of 20ºC.
• And finally, making use of sustainable energies, mainly solar: passive systems for the generation and storage of solar energy are incorporated, as well as the use and accumulation of heat.

How do passive houses take advantage of solar energy?

Here are some of the most common solutions:

• Installation of solar panels to generate electricity
• Systems for capturing and storing solar energy: heat accumulates somewhere in the house (usually under the floor).
• Roof heating system: this system that takes advantage of the heat from the roof of the house, protecting it during the coldest hours.
• Greenhouses: with translucent walls.
• Wall heating system: walls with a dark inner chamber (with or without holes, which create convection).
• Surfaces with glass.

How will you know if a house is passive? The Passivhaus standard

In the late 1980s, architecture began to lay the groundwork for a passive house standard. Bo Adamson, a professor at Sweden's Lund University, and physicist Wolfgang Feist of the Federal Republic of Germany's Institute for Housing and the Environment laid the foundations for the Passivhaus standard, which saves 70% in energy consumption compared to conventional homes. In Spain, with a milder climate, consumption is reduced by about 60% with the best energy rating for the building.

This concept focusses on the following architectural elements, included in the Passivhaus Building Platform (PEP in Spanish):

• Bioclimatic design: taking into account the climate and orientation, solar protection, etc.
• Thermal insulation: that protects from temperature changes and avoids loss of heat or cold.
• Thermal bridge prevention: creating unbroken insulation and avoiding leakage points.
• Hermeticity: by testing, a limited, controlled thermal can be guaranteed that eliminates unwanted air leaks and interior air currents.
• Windows: with the appropriate insulation and protection in each case.
• Mechanical ventilation with heat recovery: this is continuous ventilation without loss of heat or cold.
• Solar protection design: to avoid overheating.

When a building passes the tests undertaken by an expert technician, it obtains a certificate. There are several types of certificate: superior (Premium) is awarded if the building has energy self-sufficiency.

Passive houses in Spain

The first building with Passivhaus certification in Spain was the Assyce-Ecoholística house (Moraleda de Zafayona, Granada), built in 2009. Since then, numerous projects all over Spain (blocks of flats, offices, nursing homes, schools, etc.) have been awarded the Passivhaus certificate. Since awareness of renewable energies and respect for the environment has become so fashionable, the figure is expected to continue to rise and architectural trends will develop towards greater sustainability.