Design Process
What is a passive house?
The concepts of passive, ecological, and efficient houses are currently very much in vogue. Many clients confuse these terms with modular or prefabricated houses, while others ask us to explain the differences between the various types of homes.
Amidst this confusion of concepts and options, today we will attempt to explain why building a passive house is an excellent choice.
In short, a passive house is a conventional home that incorporates passive architecture strategies—also known as bioclimatic architecture—to create a comfortable indoor environment with zero or near-zero energy consumption.
From this starting point, our passive house can be more or less ecological depending on the materials and construction processes employed. It can also be more or less energy-efficient based on how much we manage to reduce consumption; a passive house can achieve zero consumption and even produce more energy than it consumes.
And what is the difference between a passive house and a Passivhaus?
This is one of the first questions our clients ask. More than 25 years ago, a group of German architects and engineers, pioneers in energy efficiency, decided to establish construction standards for passive houses that would be certified with an international efficiency seal.
The extent to which this seal is necessary is a personal matter for each client. Naturally, this certification involves an additional cost, as it requires a certified engineer to verify that the house meets the established efficiency requirements.
Many of our clients prefer not to certify and instead invest the cost of certification into the house itself. However, it is true that for individuals who may wish to sell their home as an efficient property in the future, the Passivhaus seal can be an attractive asset for the international market.
Following this clarification, let us now focus on the generic concept of a passive house, beyond the scope of certification.
Passive houses utilize various bioclimatic architecture strategies, such as the use of courtyards, porches, south-facing openings, walls that capture and store heat, high-quality insulation, or cross-ventilation to regulate indoor temperature and humidity. The goal is to reach comfort levels with the minimum possible active energy input—active consumption being defined as those systems that require energy to function, whether renewable or otherwise.
Slow Studio always works along these lines and we are open to helping any client interested in learning about and entering the world of passive houses.
What is a passive house
Starting from the beginning, a passive house seeks construction systems and finishes within the architecture itself that work in our favor to achieve the greatest possible comfort; that is, the best balance between temperature, humidity, and ventilation throughout all seasons of the year.
Once passive architecture strategies have been implemented to achieve near-zero consumption, we can utilize renewable energy systems to achieve the desired indoor comfort, especially during months when outdoor temperatures are extreme. We have very useful options available, such as solar, wind, biomass, or similar energy sources.
A passive house typically reduces its energy consumption significantly compared to a conventional house. Generally, the reduction ratio is established between 80% and 90% in relation to a conventional dwelling, particularly those built before the implementation of the CTE construction regulations.
Strategies used by a passive house
Now that we understand what a passive house is, we can begin to discuss how to achieve such a radical reduction in energy consumption in our home.
Today, there are different strategies we can adopt, provided the site and location allow for them, to reach zero energy consumption.
We will focus primarily on strategies that work in the Iberian climate, as a different strategy must be adopted for each climatic zone.
Generally, the most commonly used strategies in our latitude are:
- Capturing solar radiation.
- Generating natural ventilation.
- Increasing the home’s insulation.
- Leveraging thermal inertia.
- Utilizing the greenhouse effect.
- Generating the necessary energy through renewable sources.
1. Solar capture
Solar capture is one of the most important factors when defining what a passive house is.
In this regard, any wall or opening serves as an energy collector, provided it is well-designed.
A glazed surface or a window represents the primary heat capture strategy today. Likewise, we must keep in mind that these openings and their heat contribution to the interior must always be controllable through solar protection elements, as we must be able to avoid overheating during very hot seasons.
Conversely, in winter, we are interested in capturing as much sunlight as possible, avoiding losses due to poor enclosures, defective carpentry, or unresolved thermal bridges during the design phases.
Orientation:
Within the topic of heat capture, orientation is a vital first step to ensure the proper functioning of all other systems, in addition to acting as a highly efficient passive strategy in its own right.
It is important to orient the dwelling correctly, differentiating those rooms and partitions that will face south, north, east, and west.
Of these orientations, those with the greatest impact on the performance of a passive house are North and South. We must remember that in our latitudes, the sun moves from east to west, so the South facade will receive solar energy for the majority of the time.
It is considered logical, therefore, to orient daytime living areas or common use zones in that direction to take advantage of the sun’s heat during the day. In contrast, rooms or areas for occasional use, such as hallways, storage rooms, or bedrooms used infrequently, should be oriented to the North.
Size of openings:
Constant control of the openings made in the building’s facades is also considered very important, as they represent the most critical points and the areas through which the most significant energy losses will occur if not treated properly.
As a reference (each case must be analyzed according to the terrain and orientation), in a passive house, 70% of the south-facing wall surface should be glazed to generate the greatest heat capture for the interior of the rooms, always ensuring that the carpentry and design guarantee airtightness and that no thermal bridges exist.
In other orientations with less radiation, we must reduce this surface area since the window is the part of the facade where thermal transmittance—the heat exchange between the interior and exterior—is highest.
The surroundings can influence the size and position of windows, as there may be elements that create shadows or noise from which we wish to protect ourselves.
Solar protection systems – Filters:
This section refers to those elements, architectural strategies, or systems that allow us to protect the interior of the home from excessive solar capture that can occur, typically in summer.
While we generally seek systems to heat and capture energy, in summer we will certainly want to protect ourselves from solar radiation to maintain a cool and comfortable interior.
To achieve this, we can use porches or pergolas that allow us to block or soften the sun’s rays in summer, while in winter, they would pass through without issue.
Furthermore, a widely used resource for pergolas is the placement of deciduous vegetation, so that in summer it will be much more opaque than in winter, allowing us to avoid or capture light appropriately.
Another strategy involves solar filters on windows, with the primary objective of protecting openings from excessive radiation. The protection must be placed on the exterior face of the glass. There are many types and models of filters available; as they are facade elements, they contribute to the aesthetic of the building’s skin.
Solar capture systems – The Trombe wall:
The Trombe Wall is a passive solar capture system frequently used in bioclimatic architecture.
It consists of a wall oriented toward the most favorable sun position throughout the day. To obtain good performance from the system, the materials used must be those that allow it to absorb heat as thermal mass, such as concrete, stone, or adobe.
Its principle is simple: the Trombe wall utilizes solar radiation through two facade layers. On the exterior, a transparent glass or polycarbonate is placed in front of a south-facing wall. An air space is left between them, and vents are installed to change its behavior depending on the time of year and temperature.
During the summer, it will be important to ensure good ventilation in the system to avoid overheating the indoor air. To do this, we leave the vents open, although at night, we take advantage of the fact that the wall is cold and allow air to circulate through it to cool down.
In contrast, in winter, the primary objective is to capture as much heat as possible and transmit it to the interior of the rooms, making the system function like a radiator. Air passes through the chamber between the wall and the glass and is heated by solar radiation. At night, we close all passages so that the warm air is preserved inside.
2. Natural ventilation
Having addressed solar radiation capture, let us now discuss how to generate natural ventilation for our passive house.
Generally, the objective of these ventilations is to dissipate the excessive heat generated inside the home during the summer.
Thanks to good ventilation, we can avoid the use of air conditioning—a noteworthy point in our explanation of what a passive house is, since air conditioning is a system that extremely dries out the indoor environment, leaving relative humidity at minimum levels and causing discomfort in the mucous membranes and a consequent reduction in our defenses. This is why many of us catch colds when summer begins.
In the design phase, something as simple as placing windows on opposite facades to generate what we call cross ventilation is vital to ensure the air currents that will cool our home.
Another option, particularly suitable when working on houses with large surface areas, is to create interior courtyards that allow us to ventilate all or nearly all rooms through cross ventilation.
3. Maximum thermal insulation
So far, we have discussed heat capture or dissipation strategies to explain what a passive house is, but any system is useless if we do not pay attention to the details, allowing leaks in the house. Once we reach the appropriate indoor temperature, it is very important to prevent it from being lost.
It is vital to use the correct insulation thickness. In a passive house, we typically install between 15 and 20 cm of insulating material, depending on the needs of the local climatic zone. This is a unique aspect of this type of housing, as we are commonly accustomed to seeing houses where the thickness does not exceed 10 cm.
Another aspect to consider is ensuring the absence of thermal bridges throughout the entire building envelope.
A thermal bridge is an interruption in the insulating material or a poor resolution of an enclosure that creates a direct connection between the interior and the exterior.
This usually occurs when construction details are not well-resolved. For this reason, we consider it very important to take the design phase into account, allowing ourselves to be guided by experienced architects to review all these points and avoid errors that will be detrimental in the future.
4. Thermal inertia
Another major aspect when discussing what a passive house is involves the topic of thermal inertia.
This concept refers to a material’s ability to store heat.
When we say a material has thermal inertia, we mean that it will capture and accumulate heat and gradually release it into the cooler room. This system will help us maintain a comfortable temperature during cold periods.
The most common materials with high thermal inertia are concrete, ceramic or compacted earth bricks, or the various types of stone that can be placed on both the interior and exterior of the facade.
The location of the material is not random; if we place the capturing wall on the interior, the heat we generate inside the house will be “stored” in the materials and released at night when the temperature drops.
Conversely, if we place the thermal inertia on the exterior side relative to the insulation, we will ensure that external cold or heat takes longer to reach the insulation, helping to reduce the temperature exchange between our house and the environment.
Generally, we work with interior inertia systems while insulating on the exterior, as this has proven to be the best strategy for achieving efficiency in our climate.
Finally, great attention must be paid to the terrain on which we build because, like some materials, the ground also has significant thermal inertia and can serve as natural insulation if the house is well-seated within it.
5. Greenhouse effect
The primary benefit of this system consists of generating overheating in a volume of indoor air, using glass as an energy collector which, in turn, does not allow it to return to the exterior.
In summer, when solar radiation is most intense, we must ensure comfort by protecting solar inlets with opaque filters that prevent indoor overheating.
6. Use of energy from renewable sources
Finally, a last note to understand what a passive house is and how we can implement it.
In some cases, especially in homes located in places with extreme temperatures, we must ensure that the house always maintains the appropriate level of indoor comfort.
While this is sometimes difficult due to extreme temperatures of both cold and heat, we can include an additional energy supply system to guarantee this comfort throughout the year.
When these occasions arise, it is important—to understand what a passive house is and how it works—that we opt for energy supply systems whose primary source is renewable. That is, through solar or wind energy, or through fuels such as biomass or wood chips.
Hot water can be obtained through solar panels that heat the water directly, or by heating the water through what we call a back-boiler fireplace. This involves heating a boiler with wood, chips, or biomass. The heat obtained is stored in a water tank.
These systems guarantee that as long as fuel is available, we will have hot water.
The Canadian well is a system used primarily to preheat the air we use to ventilate our home.
It works through an installation of pipes in the subsoil, where the temperature remains constant throughout the year.
Given this situation, the sensation will be that in winter, the air coming from the Canadian well will be warmer than the outside air, while in summer it will be cooler.
Finally, one last system to mention: geothermal energy is the energy stored in the form of heat below the Earth’s surface.
It works very similarly to the Canadian well, as a conduit is also installed in the subsoil, but this time, instead of circulating air, we pass water through it, so that the ground preheats it to a temperature of approximately 12-15°C.
Geothermal energy, however, is usually not cost-effective for installation in a private home, as the payback period is too long.
To conclude this post on why to build a passive house, it is important to mention that for its proper functioning, personalized design for each case is essential. A design that manages to respond to the needs of the family, the terrain, and the local climate in the most efficient way possible.
To this end, we consider the role of an architect expert in bio-architecture essential, with whom we can work with total confidence on our home project.
Our studio, Slow Studio, offers this service, and we will be delighted to welcome you to answer any questions about what a passive house is and to evaluate, if applicable, its construction on your land.