10 Keys to Building a Passive House

On a planet with limited resources and a systematic growth logic, there is growing awareness of the unsustainability of this situation. It is for this reason that passive houses are gaining importance in this new way of understanding life and housing sustainably. Today we explore in depth what we call the 10 keys to building a passive house.

Indeed, to ensure our homes operate on renewable energy without compromising the comfort we are accustomed to, it is essential to minimize energy consumption. But how is such a goal achieved? And, more importantly, is it necessary to sacrifice the comfort our society has attained in recent times?

The answer lies in a self-sufficient housing model that requires minimal energy to guarantee 21st-century comforts, positioning itself as a future alternative that draws on concepts from traditional architecture—learning from history to avoid repeating the same mistakes. Thus, this amalgamation of architectural strategies shares a series of keys that we will develop in today’s article.

Beyond the 10 keys to building a passive house that we will review in detail below, we must remember that the primary objective of a passive house is to adapt to the available resources of the location.

What is a passive house?

This is not the first time, nor will it be the last, that we define the keys to building a passive house—a concept with which we identify both personally and professionally. Broadly speaking, this form of architecture combines construction systems and materials that work in our favor to achieve pleasant and healthy interior environmental conditions. The strategies for carrying out such a project are divided into passive and active—where the former utilize natural resources, while the latter employ mechanical systems to meet the remaining energy demand during months when external conditions are less favorable.

Thus, we see how one of the advantages of the passive house is the reduction in energy consumption, meaning we are minimizing the energy mortgage without sacrificing the comfort conditions we are accustomed to. Specifically, this reduction compared to a conventional house is estimated between 80 and 90%. Surprising, is it not? Below, we reveal the keys necessary to turn this apparent dream into reality.

10 Keys to Building a Passive House

We have selected a list of key strategies for building a passive house, among which we will enumerate 9 passive strategies and one active strategy, which we reserve for number 10, as every passive house requires a minimum energy input to ensure the comfort of its occupants.

1. Assess Construction Possibilities

As we have just explained, lower consumption means less energy expenditure, both for the planet and for our wallets. As with all long-term investments, clients tend to be reluctant to invest more money in the construction of their future home, but becoming aware of the advantages and future amortization of this investment can convince us. Thus, it is true that a greater initial investment will be necessary, but it is estimated that we will recover it in approximately 10 years. In fact, current construction regulations are increasingly strict in this regard, and there are European countries that already require new construction homes to have zero consumption as an essential condition for granting building permits.

On the other side of the coin, we find a contribution that is very difficult to assess in economic terms: the benefit of a sustainable lifestyle to personal health. Indeed, in the same way as Slow Studio’s philosophy, bioclimatic projects prioritize the use of natural materials produced through environmentally respectful processes, which do not contain chemicals and self-regulate their humidity—two characteristics highly beneficial to our health. As we can observe, a change in mindset is necessary when evaluating construction possibilities in terms of personal benefit and not solely economic.

2. Prioritize Solar Gain

A first step in implementing a bioclimatic house on a site involves understanding the local climate and the project’s relationship with the possibilities for solar gain and protection. Understanding the winter/summer variation in our climate, one must not underestimate the sun’s capacity to heat the house, but it will also be necessary to find ways to protect ourselves in summer without losing interior light quality. Thus, glazing will be essential in our future passive house, taking into account concepts such as orientation, size, solar protection systems, and solar gain systems.

Another common conception characterizes windows as sources of heat loss, but it must also be considered that this depends largely on their orientation. It is for this reason that in bioclimatic houses, approximately 70% of the south façade surface is calculated to be glazed, while openings in other orientations are minimized due to their lack of insulation. At the same time we orient the openings, we are also orienting the rooms in relation to their program, so daytime living spaces such as the dining room will also be oriented south to take advantage of the sun’s warmth during the day.

The counterpart comes with the need to address overheating in summer, with strategies such as porches, pergolas, and solar filters on windows. The two essential principles are leveraging the change in solar angle between summer and winter—so we can have a simple static element that protects us in summer while allowing sunlight in winter—and placing such elements always on the exterior face of the glass to avoid the greenhouse effect (which we will discuss later).

3. Leverage Thermal Mass

Thermal mass is a concept also frequently mentioned in this blog, but very important for understanding the principles on which passive strategies are based. It refers to the time a material needs to heat up, a measure directly proportional to the time it will take to release that heat. Therefore, a wall with high thermal mass will store heat from radiation during the day and then release it into the cold night environment.

In our climate, unlike how construction has been carried out in recent years of real estate frenzy, it is desirable for the wall’s thermal mass to remain on the interior and protect it with insulation on the exterior face. That is, we have a brick or concrete wall that accumulates heat inside the house, and this wall has insulation and protection on the exterior face. In this way, the heat entering through the windows or generated by the house’s own use accumulates in the wall, and it does not dissipate heat because it is insulated on the outside.

In summer, the process is reversed, and what we want to achieve is for this wall not to heat up. Therefore, we use solar protection to prevent the sun from entering the house and ventilate through openings in opposite directions (north-south). The walls of our house remain cool, and since they are insulated on the outside, they do not gain heat from sun exposure.

Materials with high thermal mass commonly used in bioclimatic housing construction include concrete, ceramic or rammed earth bricks, and stone. Additionally, it is important to consider the qualities of the ground itself as a cold-heat buffer. Semi-buried houses are an excellent way to leverage the thermal mass of the ground itself and reduce interior temperature variations.

4. Increase Insulation

Undoubtedly one of the main keys to building a passive house. This is a strategy linked to the previous concept, whose principle involves minimizing heat loss to maintain an adequate temperature inside the dwelling for as long as possible. The so-called thermal transmittance measures the speed at which a certain amount of heat is transmitted through a material—in other words, how quickly that material loses heat. Thus, increasing insulation attempts to minimize the heat exchange of the various surfaces with the exterior, with façades and roofs being the most problematic.

Compared to a conventional dwelling, a passive house must have a greater amount of insulation since it does not delegate this task to mechanical systems. While the former typically has between 5 and 12 cm of insulation, a bioclimatic house must have a minimum of 15 to 20 cm thickness. At the same time, this thickness does not have to be distributed equally; rather, it can be understood that a north-facing façade should have greater insulation as it receives less radiation and is therefore a greater source of heat loss in winter.

5. Achieve Airtightness

We must strive to achieve airtightness, that is, avoid air infiltrations that could cause a drop in the interior temperature of the rooms. The lack of air exchange with the exterior sometimes surprises many clients who think the interior air will become stale, but in passive houses, renewal of interior air is always ensured, which is in fact mandatory under construction regulations and is usually carried out through mechanical air renewal systems.

By controlling the exchange of fresh air, it can be filtered, further increasing the health benefits for occupants, especially if they live in the city.

The most important aspect regarding air renewal is the condition that the exterior air introduced does not enter at the ambient exterior temperature but that we have ways to preheat it. That is, if it is 2 degrees outside, we can preheat this air, for example, through a greenhouse or a Canadian well that circulates underground so that the fresh air enters the house at a temperature around 20-22 degrees.

6. Ensure Cross Ventilation

Effective cross ventilation is achieved when we locate openings—whether windows or doors—in opposite directions, especially on cold and warm façades, that is, north and south. This generates natural air currents due to temperature differences that increase the sensation of comfort.

The strategy involves avoiding highly compartmentalized layouts that make it difficult to ensure ventilation in all of them, as well as proposing interior courtyards that allow this exchange in a more controlled manner.

7. Invest in High-Quality Windows

As we have mentioned before, the passive house emphasizes insulation and airtightness, two characteristics that involve controlling the technical specifications of its openings, as they are the point of greatest energy loss in the building envelope.

We must pay attention to the two elements that make up the window: the glass and the frame. The glass can consist of two or three layers, between which low-emissivity chambers can be located. Likewise, the frame must have a thermal bridge break system—a concept we will develop in the next point—and correctly resolve its junction with the wall, the most problematic point.

8. Avoid Thermal Bridges

Energy losses occur through the most unfavorable point of the envelope, so all the investment in insulation can be in vain if we leave contact points with the exterior without proper insulation, that is, thermal bridges. The reality is that we live in a favorable climate where not much importance is given to certain discontinuities that are totally inconceivable in northern European countries.

However, in the case of passive houses, similar attention must be paid to the resolution of conflicting construction details—such as slab-envelope and opening-wall junctions. Added to this problem is the generation of moisture at these points, since the encounter of a cold point on a warm surface promotes condensation, which is harmful to health.

9. Use the Greenhouse Effect

The greenhouse effect consists of the arrangement of sealed glazed surfaces that allow the sun’s heat to enter but not escape back to the exterior, so it is stored inside. Thus, thanks to this mechanism, we can generate overheating of the interior air in a gallery or store heat in high thermal mass surfaces strategically positioned so that when night falls we can take advantage of this energy. Obviously, this is a strategy that is not desirable in summer, so we must design some solar protection mechanism.

10. Generate Remaining Energy from Renewable Sources

We conclude the 10 keys to building a passive house in the same way we began, remembering that the objective of a passive house should be to move toward zero energy consumption and not just the substitution of this with renewable sources. That is why we have been discussing passive methods up to this point, the only one that addresses active mechanisms. It is true that our climate can easily generate comfort situations through passive methods, but services we are accustomed to, such as electricity and hot water, require a small energy input.

Active energy generation strategies depend on each project, location, and energy demand for both cooling and heating. It is not the same to build a house in the Balearic Islands, where they enjoy an exceptionally warm climate, as in the Sierra de Madrid, where the heating demand throughout the winter will be much greater and solar input insufficient.

The needs of each family also come into play here, as well as the available budget. Energy generation options are many and range from connecting to the grid through an energy provider that guarantees clean generation through renewable plants to energy self-sufficiency via photovoltaic or thermodynamic panels to generate electricity or hot water.

In this regard, each project must be assessed individually and, above all, in close collaboration with the family, respecting their needs—again, it is not the same for a family with young children and members who work from home as for a couple without children who spend all day away. The passive and active operation of a passive house depends on the use given to it.