Everything you should know before building a passive house.

The concept of Passivhaus (passive houses) raises many questions among our clients. What are these types of buildings everyone is talking about really like? In this article, we will analyze what makes them different and discuss the fundamentals of the Passive House standard.

Passive houses are here to stay!

The years of pandemic have left their mark on society and new ways of life are here to stay. The consolidation after the confinement of new concepts such as teleworking and virtual meetings have caused us to spend more hours at home. As a consequence, new concerns have appeared among home users. For example, we give more importance to indoor air quality, outdoor spaces, and surrounding ourselves with natural elements, such as plants and water.

In addition, the fact of spending more and more time at home has allowed us to better understand the buildings we inhabit, as well as to identify their deficiencies. Unfortunately, for years, construction malpractice in Spain has resulted in buildings of poor quality, with poorly resolved construction details, and full of thermal bridges. True energy drains.

This new trend has favored the exodus from the big cities. After the pandemic, many families decided to make a radical change in their lives in search of a more peaceful rural environment.

This change of priorities in many users, added to the incessant changes in the price of energy, has caused an increase in interest in this new type of construction, passive houses.  

How do passive houses work?

The fundamental principle of a passive house is its very low energy consumption.

A good passive house is born from the study of the climate where it will be located, and optimizes the architectural solutions applied to its design, in order to reduce energy consumption as much as possible. In short, the basis of the passive house is the good design depending on the place.

In order to achieve such low energy levels, designers focus on minimizing heat loss. This is often due to unwanted air infiltrations, poorly sized thermal insulation, or poorly resolved construction junctions.

The passive house does not lose energy. That is why it is so efficient!

The human species should not deny the part of the blame that falls on it in this story, taking responsibility for the depletion of certain natural resources, and also, for the loss of biodiversity in certain regions of the planet.

And how do they manage not to lose energy? They are based on two main concepts:

First of all, a thermal envelope free of thermal bridges, that is, the insulation completely surrounds the house without interruptions.

And, secondly, a high airtightness. The designer defines a continuous tightness line. As a consequence, heat losses due to infiltrations are drastically reduced. This sealing also provides high interior acoustic comfort, that is, the house is very well insulated from outside noise. True oases of peace and tranquility!

They are so quiet that we must pay special attention to the sound levels of the facilities (ventilation machines, electrical appliances, etc.) so that they are not annoying on a day-to-day basis.

¿Cómo se ventila una casa pasiva?

Then you will say... if we are creating a bunker from which air cannot enter or leave, how do we ventilate the house? Opening the windows!! Because contrary to what gossip says, a Passive House can be ventilated by opening the windows.

Even so, the vast majority of passive projects integrate a double flow controlled ventilation system, which ensures a continuous supply of fresh air.

There are two reasons why we recommend the installation of this ventilation system:

– First, for hygienic reasons. If we do not properly ventilate the interior spaces, uncontrolled humidity levels can cause interstitial condensation in the walls of the envelope, with the consequent appearance of mold on our walls.

– The second reason, for health reasons. Controlled ventilation ensures constant CO2 levels inside. In addition, the supply of fresh air passes through filters, leaving it completely free of allergens (without pollens) or pollution particles.

What is passive in a house?

As its name well indicates, passive houses are based on the application of a series of passive criteria with a great impact on the energy efficiency of buildings. Next, we will list the most important ones: 

• THE ORIENTATION OF THE BUILDING

Passive houses apply basic concepts of architecture, often forgotten in exchange for aesthetic whims that do not adapt to the climate of the place. A previous study of the terrain, its sunlight, the prevailing winds, and the natural barriers, are essential when forging the foundations of a good passive project. It is what we also know as bioclimatic architecture.

Therefore, it is essential that the openings to the south are projected correctly, associating themselves with the daytime spaces of the house, favoring heat inputs in the cold months, and preventing this radiation in the summer months. For this reason, it is common to find solar protection systems in passive houses such as pergolas, cantilevers, porches, or more complex mechanized systems, such as blinds with adjustable, adjustable and raised slats.

In short, the ideal orientation of a passive house is south, since it allows maximizing the building's solar gains in winter, and controlling solar radiation in the summer months. In warm climates such as the Mediterranean, the west façade is the one that is most exposed to the heat of the sun.

Finally, a good orientation of the openings of the building with respect to the prevailing winds in the area, will allow us to favor passive ventilation in interior spaces.

• COMPACITY IN PASSIVE HOUSES

The smaller the surface of the enclosure that is in contact with the outside air, the lower the energy losses. That is, the more compact the house is, the more its energy efficiency will improve.

This point is less relevant in Mediterranean climates, where less compact passive buildings have been built, but where compensatory criteria have been applied, such as increasing thermal insulation, or reducing north-facing windows. In addition, in less compact projects, the same volumetry can favor the energy behavior of the building by casting shadows on itself.

• SUN PROTECTION

Sun protection is a fundamental issue in hot climates such as those on the Mediterranean coast. In the summer period, solar protection must ensure the regulation of solar radiation that penetrates into the house, preventing it from entering during the central hours of the day, where heat inputs are more important.

We differentiate two types of protections, the fixed ones (cantilevers, pergolas, porches…) or mobile ones (mallorquinas, blinds, blinds…)

Note that the sun protections must always be placed on the outside, that the horizontal slats are optimal for south orientations, and that the vertical slats must be placed in east and west orientations. 

• NATURAL VENTILATION IN PASSIVE HOUSES PASIVAS

A very common strategy in Mediterranean climates is night ventilation. Traditionally, in times of great heat, we completely close the house during the central hours of the day, to prevent the warm outside air from entering. And at night, when it cools down, we open the windows so that fresh air cools the house. This traditional method is also applied in passive houses.

In addition to natural ventilation, as we have previously mentioned, passive projects usually install a double flow controlled ventilation system with heat recovery.

• THERMAL INSULATION AND INERTIA

First of all, we will talk about thermal insulation. One of the most important tasks in the design of Passivhaus buildings is the definition of the thermal envelope. A passive house should be completely covered with a continuous insulating skin, thus ensuring the reduction of heat losses through thermal bridges.

In Mediterranean climates, houses with thicknesses between 7/8 cm on the walls and 12/15 cm on the roof have been certified.

In order to reduce thermal bridges, it is essential to apply SATE insulation systems on the outside, especially in new construction. 

On the other hand, thermal inertia, as you well know in Mediterranean climates, is a good thermal manager. So that we understand each other, the walls of a light wooden construction have very little inertia, on the other hand, concrete walls, thermoclay, mud walls... ensure a high inertia.

A wall with a high thermal inertia knows how to manage the high temperatures of a summer day, to then dissipate that excess heat at night, thanks to good natural night ventilation.

Similarly, in winter, it stores the energy that reaches it through solar radiation during the day, to supply it to the interior during the night, as if it were secondary heating.

• UNIQUE PASSIVE STRATEGIES

Sometimes singular strategies are used, such as the typical galleries of Asturias. Other warmer climates use wind towers, or solar chimneys (which take advantage of cold nights), or the so-called trombe walls.

They are ancestral strategies that can be applied in passive houses, as long as they are well applied and really help the interior comfort of the house.

What does it mean to have Passive House certification?

The Passive House Institute PHI is an independent research institute that has played a key role in developing the concept of passive houses. In addition, it is the entity that grants the passivhaus seal to buildings that meet the certification criteria.

defines the passive house as that building where we can provide the necessary energy for heating or cooling only through the minimum air flow necessary to maintain hygiene conditions in the interior rooms.

In other words, maintaining interior thermal comfort only thanks to controlled ventilation.

It is an international standard, which is applied with the same criteria throughout the world, regardless of the weather.

CONCLUSION

Passive houses are the result of the good practice of our profession, of a job well done, both by the architect and the builder. Passive constructions are a guarantee of good execution.

Strict periodic controls in the execution processes guarantee a high quality seal. A rigorous control of the watertight joints prevents the accumulated heat from escaping. The high-quality glazing and carpentry are studied in detail, and the Insulations, highly breathable, prevent the appearance of moisture that can be so harmful to our health.

These are the main benefits that a passive house will bring to your daily life, do you dare to take the step?

(Read article Ecological houses)

BIBLIOGRAPHY

– ecological architecture. An illustrated manual. Editorial G.G.

– Circular economy in the construction sector. CONAMA

– Environmental management. Life cycle analysis. Principles and frame of reference.  ISO 14040 of 2006.

PHOTOGRAPHS

– Guilhem Guinot – Instagram

– https://passipedia.org