Building a biopassive home

Passive homes are on trend. Everyone wants an eco-friendly, efficient, passive, or slow home—adjectives that refer to this new architecture. Whether because we are a family with a certain level of environmental awareness or because we are looking to save energy, the truth is that this is what the market demands, and that means companies adapt and market their products accordingly.

Even so, the reality is very complex, and many builders who have reinvented themselves as catalogue-home sellers jump on the bandwagon of trendy adjectives to label their homes as eco. It is therefore necessary to be cautious and distinguish between marketing buzzwords and the reality of the buildings.

A home can be very efficient and use little energy, yet be neither healthy nor eco-friendly. A company that offers homes with a steel structure—a material with a high environmental footprint—and insulates them with polystyrene, a petroleum derivative that does not breathe and can cause condensation and mould in our walls, may be very efficient, but it will be neither healthy nor eco.

In this context, the term “biopassive home” appears—a term that, incidentally, was registered a few years ago by our colleagues at 100×100 madera—and it refers to passive homes—those that reduce energy consumption thanks to bioclimatic design—and that are also designed to protect the health and wellbeing of the people who live in them.

In the coming months, we have set out to launch a series of articles that will explore in depth what passive homes are and the different ways of referring to them, which we will be sharing on the blog of our architecture studio.

When we consider building a biopassive home, most people are unsure about its specific characteristics and what needs to be taken into account to build one.

In today’s post, we will try to explain the most important factors to consider when building a biopassive home.

What is a biopassive home?

A biopassive home brings together two concepts that have already appeared on this blog: the bioclimatic home—i.e., a dwelling that makes use of the natural resources offered by its location—and the passive home, characterised by high energy efficiency through passive systems such as solar gain and solar protection, or high levels of insulation.

As you might expect, these are two closely related concepts, due to energy savings and making the most of the climate conditions where we are.

In addition, the term passive home or biopassive home should not be confused with Passivhaus homes, which are a type of certified home with specific insulation and airtightness requirements determined by the Passivhaus Institute in Germany, the body that certifies them as such.

Let us look at the principles for building a biopassive home.

Comfort in a biopassive home

When thinking about bioclimatic or passive homes, we often forget the benefits these types of dwellings provide when living in them. In our studio, whenever possible, we use natural, non-toxic materials made through more natural processes that are more respectful of the environment.

In addition, by achieving an ideal temperature through biopassive architecture, it is practically unnecessary to use heating or air-conditioning systems. As a result, the indoor environment maintains stable humidity of around 50%, which supports better immune system function, as it is not affected by extremely dry indoor climates that encourage dust and, with it, pathogenic microorganisms.

Land Characteristics

Before embarking on the construction of a biopassive home, it is very important to take into account the land on which it will be built. The characteristics of the site will define many of the decisions that need to be made about the project.

Location

When building a biopassive home, we select the plot based on proximity to our workplace or schools, how well connected it is to public transport, or the type of neighbourhood we are looking for. All of these factors can define the type of home we will need to build.

One of the factors that can limit us most is the regulations affecting our plot. These may restrict the square metres we can build on our land or the number of storeys we can build.

In this regard, it is important to consult an expert before buying a plot and, where appropriate, speak with the municipal technician about the regulations that affect it. In many cases, municipal regulations limit the number of square metres, the number of storeys, and distances to neighbours.

For all of this, we always review the regulations that apply to a plot before the client buys it. In this way, we ensure that we design a home that makes the most of the possibilities offered by the site conditions.

Sunlight

To build a biopassive home, it is essential to be able to take advantage of the sun that reaches the house. For this reason, in addition to choosing a good location for our needs, we must check that it is well oriented. The best possible orientation is, without doubt, south, as that is where the sun will come from for most of the day, especially in winter.

It is also important to know whether there are obstacles that block the sun, such as nearby buildings or trees, both on our plot and in the surrounding area.

Terrain Slope

The slope of the land, in addition to increasing the budget because earthworks and retaining walls are required, can be detrimental if it is not well oriented. If the slope faces south, it can offer advantages for opening up to the south and protecting us from the outdoor climate on the north-facing façades.

If, on the other hand, the slope faces north, this requires additional effort in the architectural design process to capture the sun. In this case, it will be necessary to design a home with courtyards that allow sunlight to reach all rooms.

Climatic characteristics

As we mentioned at the beginning of the post, to build a biopassive home we must take advantage of the local climate and, so to speak, take the good and insulate ourselves from the bad.
Let us give an example: in winter, we will use south-facing windows to capture all the heat that reaches our home. Once the heat is inside, we must store it through the thermal mass of walls or floors and prevent it from escaping through continuous, airtight insulation, in order to maintain that warmer indoor temperature.

In summer, as the sun is higher, porches will protect us from excessive radiation and cross-ventilation will help ventilate the home to dissipate any heat.

In this way, depending on the conditions of the place, we will use the resources that architecture offers to adapt to the existing climate.

Key points for building a biopassive home

Once the plot and the surrounding environment have been identified, we can begin to plan our future home. If, up to now, the presence of an architect was not entirely essential, it will now be vital to choose an architect who can guide us in certain decisions and lead the design project for a biopassive home.

Designing a biopassive home

The design of a biopassive home begins with the space the building will occupy on the plot and the internal layout of rooms and shared areas. Both are essential aspects for getting the most out of our home and ensuring it functions well.

The first concept refers both to the building’s position on the plot and to the external form our home will have. By placing the building, we will look for the best location to receive winter sun and, if necessary, protect ourselves from the strongest winds in the area so they do not affect us in winter.

As for the form, we are interested in a relatively compact shape, meaning less façade and, therefore, less energy exchange with the outside. This helps prevent losing indoor temperature. This is not a fixed premise, as the amount of façade will also depend on other factors such as the interior spaces we have and the inclusion of courtyards, which are very suitable in our climate.

Returning to the layout of rooms, we must first think about how we will use them and at what times of day. For example, we use bedrooms mainly in the morning and at night, so placing them on the east façade would be a good option to have light when we wake up.

Following this, the living room and dining room would be located to the south, as they are used more generally at any time of day. On the north façade, on the other hand, we would place bathrooms or other spaces such as storage rooms, even the entrance—areas used more occasionally and that do not require such tightly controlled temperatures.

Window size

As we have emphasised from the beginning, when building a biopassive home, solar gain will be essential to heat the home, especially in winter. Therefore, to ensure sufficient solar exposure, the size of the windows should cover, depending on the glazing and the room, between 12% and 20% of the room’s floor area. This would provide enough radiation to minimise heating costs.

Also, to increase energy savings, it is advisable for glazing to account for between 50% and 70% of the south-facing façade, provided we have sufficient thermal mass and use thermal glazing.

However, we do not install windows only to obtain light and radiation, but also to control ventilation in the home. For this reason, it is advisable to place windows on two or more walls to achieve cross-ventilation. This will help dissipate accumulated heat in summer and give us control over the ventilation we want.

Thermal Insulation

Once we have managed to let solar radiation into the home, our goal is to keep it inside for as long as possible. For this, it is very important to have the right thickness of thermal insulation in the façades.

The amount of insulation is one of the main differences compared to conventional homes, where, even if the minimum required thermal performance is met, the aim is not near-zero energy demand to guarantee comfort.

Avoiding thermal bridges

If thermal insulation is such an important factor when building a biopassive home, we cannot afford to have discontinuities in the insulation—that is, thermal bridges.

A thermal bridge occurs when heat energy passes from inside to outside the home, or vice versa, through a point in the element that separates inside from outside and has no barrier to heat transfer.

This often happens due to poorly resolved technical details, which is why it is important to review and resolve the most problematic points of the project.

Airtightness

We have all heard, more or less, about thermal insulation and waterproofing, but airtightness is a topic that, although important, is often overlooked.

After installing appropriately sized windows in the right place and adding good thermal insulation to maintain a comfortable indoor temperature, air leaks can undermine all of this work.

Air entering where it should not acts like a thermal bridge and can create unwanted air movement. It is important to ensure the joints of the same material, as they are often weak points in the inside–outside separation.

Thermal Mass

Once the heat is inside our home, as we have already mentioned, we must retain it indoors for as long as possible. For this, in addition to using thermal insulation, we can also rely on what we call thermal mass.

Thermal mass is a material’s ability to store heat and then release it. Therefore, if we place elements with high thermal mass, such as concrete or stone, in a location where they receive solar radiation, they will store that energy and release it when the temperature drops. In this way, in winter, materials with high mass will store heat during the day and release it at night, helping to moderate the temperature.

Having reviewed all these characteristics, we realise that building a biopassive home is not designed like most homes we find today. And as we might expect, building a biopassive home is not the same as building a conventional home in terms of cost. For this reason, the following considerations should be taken into account.

If you have any questions about how to build a biopassive home, or if you are considering building your own home, please do not hesitate to ask us.