Why Build a Passive House?

While the characteristics of a passive house are a topic we regularly address from different perspectives, today we aim to discuss why building a passive house is worthwhile.

Well, answering the question of what a passive house is could be done in a single line:

What is a passive house

Thus, in a passive house, the goal is for the architecture itself, the construction systems, and the finishes to work in our favor to achieve the most pleasant interior temperature and humidity for the majority of the year.

During the months when the exterior temperature is too low and it is not possible to maintain a comfortable interior temperature, we will prioritize heating the house using renewable sources, such as solar energy, wind power, biomass, or similar.

Therefore, when considering why building a passive house is worthwhile, we realize that it minimizes the consumption of a conventional house. A passive house should reduce consumption by 80 to 90% compared to a conventional dwelling, especially those built before the implementation of the CTE building regulations.

Regarding passive architecture, there is the concept of Passivhaus, which, while bearing some relation, should not be confused with a passive house.

How a house becomes passive

Well, once we understand what a passive house is, let us now examine how we achieve such a significant reduction in our home’s energy consumption.

There are main strategies that, unless the location does not permit, we must follow in any case presented to us. Although they are especially designed for the Mediterranean climate or similar, these strategies can be applied anywhere, giving more or less importance to some of them.

1- Capture solar radiation

When we ask what a passive house is, capturing solar radiation is one of the first topics discussed.

Of course, a glazed surface or a simple window is the primary heat capture strategy, but this has many nuances, since solar capture is accompanied by solar protection to prevent overheating in summer.

While in winter our objective will be to allow as much sun as possible to enter, in summer we must be prepared to protect ourselves from its radiation through pergolas, porches, or other elements.

Window size

As we mentioned, glazing will be essential in a passive house. And although windows are the weak points of a façade, in south-facing areas we should dedicate approximately 70% of the façade surface to glass.

When it comes to other orientations, this surface must be reduced, since the window is the part of the façade where thermal transmittance—the heat exchange between interior and exterior—is greatest, and therefore we achieve less insulation.

The size and position of windows will also depend on whether we have environmental elements that may cast shade. For example, even if we have a south-facing façade, if there is vegetation or adjacent buildings blocking the sun, placing many windows will be of no use. Moreover, it will be detrimental since the interior heat we achieve will be lost through the glass.

Orienting the rooms

The placement of rooms in our house will be equally important in relation to the sun.

Daytime living areas or common-use zones will always be located to the south to take advantage of the sun’s heat during the day. In fact, these rooms are usually the largest and, therefore, the most difficult to heat.

To the north, we will place rooms or areas of occasional use such as hallways, storage rooms, or rooms used occasionally.

Avoiding radiation in summer

Although we always speak of heating, of course in summer we will want to protect ourselves from solar radiation to avoid capturing more heat than necessary. For this, we can use porches or pergolas or solar filters on windows, among others.

The porches usually work well in our Mediterranean climate. This is because the sun’s angle in summer is higher than in winter. Therefore, a porch allows us to block the rays in summer and not in winter.

The pergolas can function similarly to porches, although their difference is that they are not completely opaque. Therefore, they must be placed appropriately, as they could become detrimental.

One of the resources used with pergolas is to place deciduous vegetation, so that in summer it will be much more opaque than in winter and we will avoid or capture light appropriately.
Regarding solar filters on windows, we find a thousand types and models in all possible colors and shapes.

Although an entire post would need to be dedicated to discussing solar filters alone to see them all, it is worth mentioning that if the main objective is to protect windows from excessive radiation, the protection must be placed on the exterior face of the glass.

Trombe wall

In addition to protecting ourselves from radiation in summer, we will also want to maximize its capture in winter. One capture strategy of bioclimatic architecture is the Trombe wall.

The Trombe wall is a system that harnesses solar radiation through two façade layers. That is, 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.

In summer, we will keep the vents open so that air circulates and does not heat the interior of our house. At night, therefore, we will take advantage of the fact that the wall is cold and allow air to circulate through it to cool down.

In winter, however, it will function like a radiator. Air will pass through the chamber between the wall and the glass and will be heated by solar radiation. At night, we will close all passages so that the warm air is retained inside.

2- Generate natural ventilation

Well, so far we have seen how to capture solar radiation to heat our house—or how to avoid it. Let us now see how to generate natural ventilation for our passive house.
The objective of this ventilation will be, above all, to dissipate the heat that may accumulate inside the dwelling in summer. Ventilation will allow us to avoid the use of air conditioning during the hottest months and significantly reduce a house’s energy demand, the main reason why building a passive house is worthwhile.

Cross ventilation is the best method we can implement to cool our dwelling. It involves, as its name indicates, incorporating windows on opposite façades in the architectural design, so as to facilitate rapid and effective air circulation.

One option when dealing with large-surface houses is to create interior courtyards that allow us to ventilate all or almost all rooms through cross ventilation.

This is what we did in a recent project in Colomers, where we placed an interior courtyard to ensure that all rooms had two façades through which to ventilate.

3- Increase the house’s insulation

The first two points about what a passive house is are dedicated to how to gain or lose heat, depending on the time of year. Well, once we achieve the interior temperature for our comfort, it will be important to prevent it from being lost.

The thickness of insulation is one of the main differences between a passive house and a conventional house. If 8 cm of insulation is acceptable in a conventional dwelling, in a passive house up to 15 or even 20 cm will likely be installed, depending on the needs of the climate zone in which it is built. But in addition to thickness, we must also pay attention to the absence of thermal bridges.

A thermal bridge occurs when the same construction element, whether the structure or a piece of the construction system, has direct contact between the interior and exterior. That is, there is no insulation layer separating the two environments.

A thermal bridge occurs when construction details are not properly resolved, which is why it is important to seek an architecture team with experience in the field of bioclimatic and passive architecture that has carried out high energy efficiency projects, correctly resolving each of the construction challenges.

4- Utilize thermal mass

Thermal mass is a concept we regularly address in our posts. It refers to a material’s capacity to store heat.

When a material has thermal mass, it means it will take time to heat up, but then when the environment is cooler it will release the heat in a way that helps maintain a more pleasant temperature during cooler moments.

Materials with high thermal mass such as concrete or stone can be placed both inside and outside the façade.

If we place thermal mass inside, it means that the heat we generate inside the house will be “stored” in the materials and released at night, when the temperature drops.

If, on the contrary, the thermal mass is on the exterior side relative to the insulation, we will ensure that the exterior cold or heat takes longer to reach the insulation. In this way, we could reduce the temperature exchange between our house and the environment.

Like some materials, terrain also has high thermal mass and can serve as insulation. For example, if we can bury part of our house and especially the north façade under the terrain, all the terrain in contact with the construction will prevent the temperature difference between one side and the other from being too great.

5- Use the greenhouse effect

The greenhouse effect occurs when heat from the sun can enter through glass but then does not return to the exterior.

This phenomenon causes overheating of glazed areas in summer, when solar radiation is more intense, especially in our Mediterranean climate.

But this does not have to be a problem; rather, we can take advantage of the greenhouse effect. If we have south-facing windows and place materials with thermal mass behind them, we will manage to store this heat in the construction itself so that it is emitted when the sun no longer shines directly.

We must not forget that it will be necessary to be able to ventilate the area or design a solar filter so that in summer the greenhouse effect is not counterproductive.

It involves using the same system as greenhouses or winter gardens, which capture all the heat, and once inside, it is more difficult for it to return to the exterior.

Well, so far we have seen what it is, how we achieve it, and why building a passive house is worthwhile.

But while it is necessary to achieve comfort in a dwelling, we must ensure that in case of extreme temperatures, both cold and heat outside, the house does not overheat or excessively reduce its temperature.

Therefore, a passive house usually includes some additional energy supply system to guarantee comfort throughout the year.
It is important that this energy supply is provided as much as possible through renewable sources, that is, through solar energy, wind power, or fuels such as biomass or wood chips.

Let us examine the strategies available today within the field of renewable energy:

Electricity

To obtain electricity autonomously and renewably, we basically have the option of solar panels or wind turbines.

Solar panels capture solar radiation to generate electricity through chemical processes. This energy is often stored in the form of hot water, but if what we want is to store electricity as such, one of the best solutions is likely to use a Tesla battery.

Another possible strategy is to install a domestic wind turbine; however, these systems are less widespread because we need a constant supply of wind to obtain energy and they usually have to be combined with solar capture systems.

Hot water

As with electricity, we basically have one option: we can obtain hot water in two different ways. The first is through solar panels that directly heat the water. Furthermore, storing hot water is easier than storing electricity. The second option is to heat water with a fireplace boiler. This involves heating a boiler with wood, wood chips, or biomass, the heat from which is stored in a water tank, guaranteeing that as long as fuel is available, we will have hot water.

Canadian well

The Canadian well, more than a way to obtain energy, serves to preheat the air we will use to ventilate our house. It involves running a pipe underground, taking advantage of the fact that it is at a more or less constant temperature throughout the year.

Compared to the exterior air temperature, a Canadian well in winter will heat the air passing through the duct, and in summer it will cool it.

Geothermal energy

Geothermal energy is the energy stored in the form of heat below the earth’s surface.

Its operation is very similar to that of the Canadian well, as a duct is also installed at a certain depth. But this time, instead of circulating air, we pass water, so that it is preheated to an approximate temperature of 12-15°C.