Design Process
Design of a Biopassive House
Passive houses are currently in vogue; who wouldn’t want a home that consumes no energy, or rather, generates it without relying on the grid?
In recent years, hundreds of companies have emerged selling eco-houses, passive houses, efficient houses, and zero-consumption houses. What is the difference between them, and how can we clarify this set of terms?
The reality is that even ecological house builders themselves are often unclear on the term. If we are to be radical, an ecological house should not only be zero-consumption and efficient, but its materials should also respect both the environment and its inhabitants.
In this regard, at Slow Studio, we have specialized for years in building ecological and healthy houses—that is, zero or near-zero consumption homes (depending on the budget and the site’s potential) that are in harmony with the people who inhabit them, generating a healthy interior environment with natural ventilation, free from toxins and radiation of all kinds.
What do we call this type of house?
For us, it is the type of house that all builders and architects should design. However, as the market is still light years away from building this type of home, those of us who champion them are known as “ecological” or “passive house designers,” or “biopassive” if we include the term “bio” in relation to everything living, to health, and to the people who inhabit the homes. (The term “biopassive houses” is, by the way, registered by our colleagues at 100×100 madera).
And precisely today, we want to tell you how these types of houses are designed: houses that capture heat from the sun, store it in winter, and protect themselves from it in summer; houses that breathe and ventilate naturally without air conditioning; houses whose materials are chosen with extreme care so they do not emit toxins into the environment; houses without waterproof paints that prevent natural humidity regulation; houses that generate energy through solar panels—in short, an efficient and healthy home.
What does biopassive house mean?
Well, first of all, let us analyze the composition of this word. Let us divide it into BIO – PASSIVE.
As one might expect, part of the term involves the concept of a passive house—that is, those zero-consumption ecological houses that reduce domestic energy expenditure, saving us from electricity, gas, and water bills without depriving us of the comfort a conventional home would provide. They work with natural and healthy materials that breathe and generate a healthy indoor environment, maintaining pleasant temperature and humidity levels while ensuring they are free from toxins.
On the other hand, the term BIO introduces an additional input: the fact of taking advantage of and utilizing the natural resources of the environment and the location where we are situated.
Likewise, we can also relate this “bio” to biological. A house of this type, a biological one, prioritizes people’s health above all else; therefore, it will be a house free of toxins, chemicals, and radiation of all kinds.
Sounds like a dream, doesn’t it? Surely the next question is: How much does a biopassive house cost? Is it more expensive?
The best part is that all of this can be achieved without the need for large investments, provided that the right strategies are employed. We can draw inspiration from traditional architecture, which used passive resources to ensure comfort. Opening windows, orienting rooms correctly, and designing openings and their filter and protection systems are examples of these strategies.
Design of a Biopassive House
As mentioned, a biopassive house merges two concepts:
Firstly, that of the bioclimatic house—that is, a dwelling that takes advantage of the natural resources offered by the site without losing sight of the “bio” concept referring to biological factors that affect people.
And secondly, the passive house, characterized by its high energy efficiency through passive systems, whether through solar gain, solar protection, or high levels of insulation.
The strategies of this architecture use design elements or the architecture itself to achieve energy gains. For example, a window placed with a southern orientation or a porch to protect us from the sun in summer are simple strategies that help us understand how a passive house works.
These two concepts are closely linked, both in terms of energy savings and the utilization of climate conditions.
Finally, there is a third concept implicit in the definition of a biopassive house: its relationship with the biological. Thus, a house of this type takes great care to preserve and improve the health of the people who inhabit it. It is, therefore, a house free of toxins, chemicals, bacteriological agents, and radiation of all kinds.
Thus, the design of a biopassive house should take into account:
1. Bioclimatic design adapted to the conditions of the site.
2. Inclusion of energy efficiency strategies from passive architecture.
3. Working with natural and breathable materials that generate a healthy indoor environment.
Let us go into detail on each of these points:
1. Bioclimatic design adapted to the conditions of the site
Before starting to build, we must pay special attention to the land where we will erect our house. Where are we located? What is this place like?
The characteristics of the site will largely define many future project decisions; therefore, a thorough study of the location, occupation, implementation on the land, shape, porosity, compactness, etc., is vital to have a solid documentary basis to work from.
Location
The choice of location is often conditioned by personal preferences, such as proximity to work, schools, good connections to public transport networks, or even the type of neighborhood that interests us.
Once we have the plot, current regulations may limit or condition the type of construction we can build on it. There may be restrictions regarding the built area, maximum height, alignment with the street line, materials, facade tones, etc.
To avoid unforeseen issues, it is important to consult with an expert before purchasing land and, if necessary, speak with the municipal urban planner regarding the regulations governing our plot.
Our team at Slow Studio always reviews the regulations applicable to a piece of land before the client purchases it. In this way, we design based on knowledge, ensuring that the house we build complies with all regulations while simultaneously taking advantage of all the possibilities the site offers.
Sunlight
One of the main characteristics in the design of a biopassive house is ensuring that it makes the most of the energy and natural light from the sun, especially in winter. For this reason, besides choosing a good location, it is important to look at the sunlight conditions of the site—that is, its orientation relative to the daily movement of the sun.
The best orientation in our latitudes is, without doubt, south-facing, as it ensures good general lighting for most of the day, even in winter. In summer, it is recommended to filter and dose this radiation if we want to avoid excessive heating inside the home.
One must consider obstacles that may affect the lighting of the site, whether they are other nearby buildings or elements of vegetation outside or within the plot.
Terrain Slope
The topography of the land is another characteristic to consider in the design process of our house.
It is usually inevitable to have to modify its morphology, using machinery for earthmoving and building systems or retaining walls to properly settle our building.
These procedures usually increase our budget, but by using the appropriate implementation strategies, we can take advantage of the topography itself to improve the conditions of the dwelling.
Generally, we should avoid north-facing slopes, although by using interior courtyards, we can facilitate the lighting of all rooms inside the home.
In contrast, south-facing slopes are ideal and advantageous, as they allow for a facade that receives full solar radiation, while we can shelter and even partially bury the north facade in the earth itself, naturally insulating the wall.
Climate
Regarding climatic conditions, we must take advantage of the benefits of each local microclimate.
We have clients who buy land 20 kilometers from a large city where climatic characteristics can vary, with temperature differences of up to 4 degrees less throughout the year.
It is necessary to know the meteorology and climatic characteristics of the place where we settle our construction.
Once we have performed this analysis, we can select which architectural resources and strategies we will use to adapt to and make the most of the opportunities provided by the existing climate.
In winter, for example, solar radiation is lower and temperatures are colder. Inside the home, we want to ensure comfort, so we must store and conserve as much heat energy as possible. Windows capture and transmit this energy into the home; thick walls also gradually accumulate heat, transporting it from the outside in and providing it to the rooms at night when it is colder outside. This is an ideal strategy, although it is useless if the house’s insulation is poor and we quickly lose all this energy.
In summer, the same elements treated differently can also be useful. Windows, this time open and on opposite facades, generate pleasant air currents that help ventilate and cool the house. The incorporation of porches or natural or architectural filters on the facades that receive the most sun will prevent excessive heat gain by the walls. Vegetation can be integrated into the architectural design, as it generates air and maintains a fresh and healthy environment while filtering the sun’s rays and creating pleasant shaded areas.
2. Design Strategies for a Biopassive House
All these preliminary steps, especially the analysis and assessment of pre-existing conditions, must serve us when planning the design of our future home.
It is important, especially at this point, to have a trusted architect who can guide us in decision-making as well as in the planning and design of a biopassive house.
The design—that is, the project phase—is very important. In it, we will consider all the conditions and characteristics of the location, sunlight, climate, and topography of our land to correctly choose what our biopassive house should be like.
Implementation on the Land
We will begin by determining the space the construction will occupy. The structural and foundation surface must be considered. Next, the perimeter of the house, which will likely be linked to the interior distribution and space of each room, distinguishing between common areas, private areas, and service areas.
The implementation must identify the most suitable spot on the plot—the one that receives the most sun in winter and that, if they exist, protects us as much as possible from unfavorable winds that could jeopardize our well-being.
These elements, as well as others such as potential noise disturbances, can also be addressed with architectural protection strategies or vegetable barriers.
The shape or volume of the building should generally be compact to ensure the utilization and accumulation of energy at one point. Furthermore, reducing the facade surface area avoids unfavorable energy exchanges.
This premise may vary if, for example, as mentioned earlier, the slope of the land is unfavorable (north-facing) and our typology must include a system of interior courtyards in our design, generating small, pleasant, and bright microclimates throughout the rooms of the house.
Solar protection (porches, protection of openings according to orientation—south, east, west—vegetation…)
Although it is very important to orient the house to capture as much energy as possible, in summer we will want to protect ourselves from solar radiation to avoid capturing more heat than necessary. To achieve this, we can incorporate porches, pergolas, or solar filters on the windows into our design, among others.
Firstly, and considering our (Mediterranean) climate, porches usually yield good results. The sun’s angle in summer is higher than in winter, which is why a porch will protect us from radiation in summer but allow us to receive it in winter.
Pergolas work similarly, although they are not completely opaque. They must be placed correctly, as they could potentially be detrimental; a pergola that is too extensive could prevent sunlight in winter, which would not allow us to accumulate heat inside.
In this case, planting deciduous vegetation can help, achieving more opacity in summer and radiation permeability in winter.
Regarding solar filters, there are many types and models. To choose, we will have to consider our main objective—that is, protecting the windows from excessive radiation.
Regarding filters, it is important to distinguish between the orientations of the dwelling: a western orientation requires filters with adjustable vertical slats, as this is where the sun sets and where solar radiation is more horizontal.
A southern orientation, by contrast, always receives the sun more directly and vertically, thus requiring protection in the form of pergolas or porches.
Capture and Storage of Solar Heat (South-facing openings + thermal inertia)
From the beginning, we have insisted on the importance of solar capture when building a biopassive house.
To have sufficient sunlight and depending on the type of glazing, the size of the windows should occupy between 12% and 20% of the floor area of the room in question.
With this average surface area, we will manage to provide enough radiation to minimize heating consumption as much as possible, although we must always keep in mind that the proportion of openings will depend on the orientation of the facade and the desired result.
Likewise, we can save energy by opening windows in 50-70% of the southern wall surface, provided we have sufficient accumulation mass (wall thickness) and use thermal glass.
Airtightness and Insulation
Another objective to undertake is to conserve all that radiation captured by windows and walls inside. The thickness of the wall itself must be appropriate, as must the thermal insulation we provide on the facades.
This thickness—that of the insulation—is characteristic of biopassive houses and differs from conventional ones, as the latter are limited to meeting the minimum required thermal performance, whereas the design of a biopassive house must ensure comfort with near-zero energy consumption.
At this point, it is important not to overlook the issue of airtightness.
Once the windows are located and the insulation is defined (surfaces to cover and thickness), we must not forget to ensure there are no air leaks that would waste all the design and construction effort to maintain a good interior temperature; this is achieved through rigorous control of construction details in both the project and construction phases.
Facilitating the renewal of stale air is mandatory in any home, but this is very different from air entering where it shouldn’t due to poor design control. These leaks create thermal bridges and unwanted air circulation. Therefore, it is important to ensure airtightness in the joints between materials, as these are ultimately the weak points in the path between the interior and exterior.
Natural Ventilation
Although it may seem contradictory, we must ensure that our house has its own ventilation systems, whether to renew stale indoor air or to cool it in case of excessive heat.
An air current of just 3 meters per second (that is, 10.8 kilometers per hour) manages to reduce the thermal sensation by approximately 1°C.
But how can we generate these currents and introduce them correctly into our home?
Easy! Through cross-ventilation, a natural system with which we can refresh the environment without the need for machines or mechanical systems.
By simply placing windows on opposite facades, we facilitate the air’s ability to generate an opposite path between a cold facade and a hot one, producing a current that refreshes the environment and, in the process, renews the indoor air. The only thing to keep in mind is that there should be no obstacles or walls preventing this path.
It is very common in the design of a biopassive house to have interior courtyards that serve as a controlled outdoor space through which to ventilate bedrooms or other rooms, while also providing light to rooms that may be far from the facades.
3. Building with natural and breathable materials that generate a healthy indoor environment
In the design of a biopassive house, we cannot forget the concept of health.
Surely at some point we have asked ourselves: What is all this for? What benefits does it bring me?
When we think about the design of bioclimatic, passive, or biopassive houses, we must not forget that, besides creating a sustainable home, these houses add something extra to our lives: interior comfort comes from zero-consumption strategies, and the use of natural materials is an additional input that seeks to care for our health as well as that of our environment.
The design of a biopassive house can achieve an ideal temperature without even using heating or air conditioning systems. This allows the indoor environment to maintain a stable humidity of around 50%, thus enabling better functioning of our immune system, which is not affected by extremely dry indoor climates that favor the appearance of dust and, with it, the proliferation of pathogenic microorganisms.
The choice of materials is a decisive preliminary step to ensure the overall good functioning of the home. Furthermore, building with natural and breathable materials will foster a healthy indoor environment beneficial to the health of its inhabitants.
It is recommended, and consistent, that the materials we choose be local as far as possible. By using local materials, we promote production in our area and save on transport costs.
For the wall structure, it is recommended to work with natural materials such as wood, as well as ceramic or stone materials that have manufacturing processes with a reduced ecological footprint. If the budget does not allow for this, we will at least try to use healthy materials for the interior surfaces.
The Biopassive House as a Future Investment
With all this, we can quickly realize that the design of a biopassive house involves specific knowledge, techniques, and systems different from conventional constructions.
Therefore, the cost may also be different, but in these cases, a firm commitment to the future must be made.
Construction Cost
In the construction phase, and compared to other types of housing, there is a certain extra cost in the case of biopassive houses. This extra cost is normally linked to the investment in a greater amount of thermal insulation, higher quality windows with better thermal performance, etc.
In other words, the choice is for good, durable elements that, despite the initial economic increase, will more than compensate us by not having to pay heating or air conditioning bills, etc.
Furthermore, we can also offset the investment with simpler construction solutions and materials of local origin to save on transport.
Finally, it should be noted that in no more than 10 years we will have amortized the initial investment; therefore, after this period, we will have recovered that extra cost and will begin to save all the energy we will not have to use to heat or cool our house.
Energy Savings – Benefits –
Regarding energy savings, a biopassive house reduces the consumption of a conventional dwelling by 80% to 90%. This represents a beneficial saving for both the environment and ourselves.