Although there are different criteria and approaches to conceiving this type of dwelling, there are a series of fundamental principles worth considering. In this article, we compile the essential keys to understanding what defines a passive house and how this translates into a real architectural project.

In our studio, we receive many people who are clear that they want a passive house, but it is common to find confusion: there is a tendency to associate passive house with timber house, or to believe that a passive house must necessarily have Passivhaus certification.

We always insist on the same thing: a passive house is, above all, a well-designed and well-built home.

Well-designed, because it is designed to adapt to the environment: with openings oriented to the south that allow solar capture, strategically positioned daytime areas, natural north-south cross ventilation, solar protections such as porches, overhangs or louvers, thick walls that accumulate heat, and excellent insulation that prevents that heat from being lost. All of this forms part of a rigorous approach that we develop in detail later.

Well-built, because materials and technical solutions are not chosen at random. Materials with thermal mass capable of storing and releasing heat efficiently are used, breathable insulation that prevents condensation, perfectly airtight joints to minimize energy losses, carefully calculated high-efficiency glazing… And all of this is not only designed, but requires exhaustive control during construction.

Furthermore, a passive house is closely linked to vernacular architecture, that architecture which over the centuries has adapted to the climate of each place. Building a dwelling in the Pyrenees is not the same as doing so by the sea in Alicante. Observation of local construction techniques and the use of local materials give us clues about which solutions have historically worked in each region, often the result of a long process of trial and error.

Of course, today architectural design has evolved into what we know as architecture 4.0: what was once knowledge transmitted through generations is now validated with 3D models, thermal simulations, and precise mathematical calculations. But it continues to be based on the same logic: making the most of available resources to generate interior comfort without resorting to active systems.

In short, when we ask ourselves what a passive house is, we are talking about a dwelling designed with climatic common sense, where intuition and local experience become a technical strategy capable of generating comfortable spaces throughout the year with minimal energy consumption. All of this is supported by energy demand studies that allow us to know, before building, what temperature each room will have in each season of the year, and thus adjust each project decision—such as the amount of insulation needed—to guarantee the final result.

What characterizes a passive house?

The basic principle that defines what a passive house is is the reduction of energy demand through so-called passive systems. These systems are characterized by not requiring energy consumption to function, as they take advantage of climatic conditions and the physical characteristics of the building to guarantee interior comfort.

Some examples of passive systems are good thermal insulation, proper orientation of rooms and their openings, which must also have effective solar protections for summer, or the selection of high energy-efficiency windows and glazing. All these elements work together to minimize the need for mechanical heating or cooling.

Once we have designed the dwelling following passive criteria, the next step is to cover the remaining energy demand. This is where active systems come into play, which do consume energy, although this can come from renewable sources. This is the case, for example, with photovoltaic or thermodynamic solar panels, which allow electricity or domestic hot water (DHW) to be generated sustainably.

When we manage to ensure that all the energy needed to cover these demands—such as heating, hot water for bathrooms and kitchen, or electricity for lighting and appliances—comes from renewable sources, we can speak of a zero-consumption passive house. It is important to remember that, following current comfort standards, even in very efficient dwellings there will always be a certain energy demand to cover, especially in cold climates or depending on usage habits. The key is that this demand be minimal and can be satisfied cleanly and efficiently.

1. Solar capture / protection

To understand what a passive house is, it is key to know how solar radiation is managed throughout the year. In climates such as the Mediterranean, with hot summers and cold winters, the strategy must adapt to the season: in summer, the sun is higher and radiation is intense and vertical, while in winter it is lower, horizontal, and less abundant. Therefore, the objective is to capture solar heat as much as possible during winter to heat the interior, and in summer to protect the dwelling from radiation to avoid overheating.

Orientation is decisive in this strategy. The south facade is the most efficient for solar capture in winter, followed by the east and west facades. In contrast, the north orientation receives very little radiation, remaining in shade most of the day.

Beyond installing conventional windows with shutters, the design of a passive house makes the most of this natural resource. Different solutions can be employed: carefully selecting the type of enclosure, the number of panes and air chambers, or the degree of transparency of the glazing.

As for solar protection, the options are very varied: pergolas, adjustable shutters that allow light and ventilation, eaves, or even deciduous vegetation, which protects from the sun in summer and lets light through in winter. Each of these elements contributes to passively regulating interior temperature, reducing the need for artificial climate control.

2. Thermal mass

When we talk about what a passive house is, one of the key concepts is thermal mass. This term refers to the capacity of a material to accumulate heat and release it gradually. The greater the mass of the material, the greater its storage capacity.

A material with high thermal mass captures and stores heat gradually, releasing it slowly when the ambient temperature drops. This generates a lag between the temperature of the material and that of the exterior, which is very beneficial. In winter, for example, solar heat can be stored during the day and released at night, maintaining a comfortable environment even when it is colder outside.

In summer, if we protect the walls to prevent them from accumulating heat, thermal mass allows us to preserve nighttime coolness indoors and avoid overheating during the hottest hours.

A very effective passive strategy to take advantage of thermal mass is to semi-bury the dwelling, since the ground has a large thermal mass that dampens temperature changes. Other materials with high thermal mass are concrete, stone, ceramic brick, or compacted earth.

In modern passive houses, these materials are preferably placed on the interior, since exterior insulation is very efficient and we want to preserve heat in winter or coolness in summer. In the past, when insulation was not used, thermal mass was exploited in very thick exterior walls—as in stone or earth houses—that accumulated heat during the day and transmitted it to the interior with a lag of several hours, keeping nighttime temperature more stable.

3. Insulation

Thermal insulation is one of the pillars that marks the difference between conventional construction and a passive dwelling. Its function is simple but crucial: to prevent the heat or coolness of the interior from being lost to the exterior and vice versa. Thus, once the ideal temperature inside the dwelling is achieved, insulation maintains that comfort stable without the need for continuous energy expenditure.

In traditional construction, insulation is usually insufficient, which forces reliance on heating or cooling systems for much of the year. Following the principles of a passive house, thickness is significantly increased: compared to the 5-8 cm typical in old buildings in Spain, 15 to 20 cm are installed, which drastically reduces energy demand.

Furthermore, not all facades are insulated equally. Those oriented to the north, for example, receive less solar radiation and are more prone to thermal losses, so it is advisable to reinforce their insulation or even semi-bury them to take advantage of the ground as natural protection and thermal mass.

Openings—windows and glazed doors—are the most vulnerable points of the envelope, as they have less insulation. Therefore, investing in high-quality windows and high-performance glazing not only improves efficiency, but also prevents interior comfort from depending on active climate control systems.

4. Absence of thermal bridges

The efficiency of a passive dwelling depends not only on the thickness of its insulation, but also on it being continuous and without interruptions. Thermal bridges are precisely those breaks in the insulating envelope that directly connect the interior with the exterior, allowing heat loss in winter or heat entry in summer.

In a section drawing, the insulating layer should be able to be followed with a continuous line, without lifting the pencil at any point. Floors, slabs, roofs, windows, and structural junctions must be protected, even if this requires combining different insulating materials.

When a construction detail is not resolved correctly, the thermal bridge becomes the weakest point of the envelope, compromising thermal comfort and increasing energy consumption. In temperate climates, this problem often goes unnoticed, but its effects are felt: the most problematic areas are usually the junction of the slab with the facade and the junction between the window frame and the wall.

In addition to energy losses, thermal bridges can generate condensation when a cold point is combined with a warm, humid environment. This not only damages materials, but can also affect the health of occupants, reinforcing the importance of eliminating them in the design and construction of a passive house.

5. Natural ventilation

Natural ventilation fulfills two essential functions: one related to climate comfort and another directly linked to the health of those who inhabit the dwelling. From a climate perspective, it allows accumulated heat to be dissipated from the interior during the warmer months, taking advantage of the natural movement of air to cool spaces without resorting to mechanical systems.

As for health, ventilation promotes constant renewal of interior air, eliminating impurities, reducing CO₂ concentration, and regulating humidity levels. This process helps prevent problems derived from a closed and unhealthy environment, such as the appearance of mold or the proliferation of dust mites.

To optimize it, it is key to use cross ventilation, which consists of placing openings on opposite facades, preferably oriented to the north and south, to generate effective air currents. It is also possible to use interior courtyards that, strategically located, facilitate air exchange between different rooms and improve the environmental quality of the entire dwelling.

Energy consumption

Active systems are those that require an energy input to function, whether from renewable or non-renewable sources. Before delving into them, it is advisable to analyze the annual energy consumption of different types of dwellings to understand the scale of the issue.

A dwelling is considered passive when it manages to reduce consumption by at least 80-90% compared to a conventional house. This consumption includes not only the energy for climate control, but also that necessary for the operation of appliances, lighting, production of hot water, and cooking. Even water use—which we will see later—influences total consumption.

In Spain, the average annual expenditure of a conventional single-family dwelling is approximately 150 kWh/m². In a 100 m² house, this represents about 15,000 kWh per year, of which around 65% is allocated to climate control (heating and cooling), while the remaining 35% corresponds to the use of appliances, lighting, cooking, and domestic hot water (DHW).

Reducing the weight of climate control in total consumption is key, and this is precisely what passive construction strategies achieve. The objective is to minimize the energy needed for heating and eliminate, as far as possible, the use of active cooling systems.

The Passivhaus standard, originating in Germany, serves as a reference. It certifies dwellings with a maximum consumption of 15 kWh/m² per year for both heating and cooling. If we apply these values to a 100 m² dwelling, the annual expenditure would be 1,500 kWh to heat it, equivalent to the consumption of a hair dryer running for the same time.

To this is added the demand for primary energy—that needed for lighting, appliances, cooking, and DHW—which, not counting climate control, is around 5,000 kWh annually in a 100 m² dwelling. This figure can be reduced through efficient appliances, complete shutdown of devices on standby, and use of natural light, although there will always be a minimum consumption for daily life.

Renewable sources

Renewable energies can be used to generate heat or electricity. In the case of lighting, appliances, and cooking, electrical energy is essential, while heating and DHW can be resolved with thermal energy.

Generate electricity

For total self-sufficiency, current options are wind and solar energy, that is, photovoltaic panels or wind turbines. However, electricity storage remains a challenge, so many installations feed surplus into the electrical grid and consume from it during periods without production, such as at night. This situation could change in the coming years with advances in energy storage technologies.

Heat water

Both DHW and heating in a passive dwelling are resolved with thermal energy. While it is true that many conventional dwellings consume gas, a fossil energy source that heats water to very high temperatures, renewable energy sources have other implications.

Below, we will evaluate the different methods for generating thermal energy: