How does a Passivhaus home work?

We frequently discuss the topic of passive houses, and in previous articles, we have introduced the concept of homes with the Passivhaus seal. In today’s post, we will delve deeper into this concept, explaining what a Passivhaus home is and how it functions.

To do so, it is helpful to refresh our memory and first review what passive houses are, especially for those clients who often consult us on how to build an ecological home. Nowadays, we have access to such vast and varied information that it is natural to feel overwhelmed by the multiple construction possibilities and different types of eco-friendly houses offered by the market.

Let’s begin!

A passive house with Passivhaus certification

Precisely to devise a method or system that could measure and classify the level of passivity of a house, a team of German experts in energy efficiency created the Passivhaus seal in 1988.

This seal grants an internationally recognized certification to those dwellings that meet specific requirements regarding climate control and primary energy consumption.

Firstly, the design of a Passivhaus home must meet certain criteria based on passive architecture strategies, reducing the need for heating or air conditioning to climate-control the interior of the dwelling.

This is achieved through a passive architectural design whose efficiency allows the house to heat and cool itself using natural and sustainable systems. Heat is captured from the sun and dissipated through air currents.

Once our home has reduced its energy needs and stored enough heat, the remaining input is minimal and can be achieved with very little energy.

Finally, and as a more precise figure, the Passivhaus seal is awarded to a house if it incorporates sufficient energy efficiency strategies (good insulation, proper orientation, airtight walls, solar protection in summer, etc.) and manages to reach a minimum heating expenditure (below 15 kWh/m² per year).

What is a Passivhaus Home?

As a reference, a house with the Passivhaus seal will be one that manages to reduce heating and cooling needs by approximately 75% compared to a conventional house.

This implies significant energy and financial savings simultaneously; with a small initial investment, we can save a substantial amount of money on heating and air conditioning costs. These costs, besides negatively impacting global warming, typically rely on non-renewable sources and can be detrimental to health.

Should an extra energy contribution be necessary, homes with the Passivhaus seal can turn to renewable energy systems that do not depend on a utility company and respect the environment.

Passivhaus energy certification

To clarify and specify further, let us now focus on the Passivhaus energy certification.

As previously mentioned, the Passivhaus seal is essentially a certificate ensuring that our dwelling has lower heating and climate control expenditures than a conventional house; in other words, we live in a nearly zero-energy or zero-energy home.

It is awarded to houses that meet a heating expenditure of less than 15 kWh/m² per year, but there are actually other options that must be considered.

To obtain Passivhaus certification, we always recommend seeking the assistance of an architecture firm expert in the field that, in turn, works alongside official Passivhaus certifiers who support the firm throughout the entire design process of a Passivhaus home.

The Passivhaus certification technician supervises the entire design and construction process of a Passivhaus home. At the end, they perform a series of tests and measurements to verify and demonstrate that all the requirements established by this seal are met, certifying that the house complies with the energy requirements of the Passivhaus standard.

These requirements correspond to a series of very specific demands regarding the dwelling’s consumption. It is established that:

How a Passivhaus home works

As we can observe in the requirements established by the Passivhaus certificate, it mandates a lower energy demand while avoiding excessive air exchange to help reduce climate control consumption.

But the big question is:

Let’s look at each of the steps to follow to understand how a Passivhaus home works.

Thermal Insulation

In a Passivhaus home, as in any energy-efficient house, the thickness of the insulation is always greater than in conventional ones.

Logically, this thickness will also depend on the climatic zone where we are located, but it is usually no less than 15 cm thick. The function of thermal insulation is to ensure that the interior environment of a house is not influenced by external weather conditions, making it much easier to control its temperature.

The primary goal is to prevent cold from entering in winter or heat in summer, maintaining a stable indoor temperature and humidity.

If we add natural capture and ventilation strategies to this, we will manage to maintain an optimal temperature for most of the year without energy consumption.

Avoiding thermal bridges

All the work and investment in thermal insulation would be in vain if we did not then pay attention to construction details, leaving points of contact with the exterior without proper insulation.

A thermal bridge is a discontinuity in the insulating material that occurs when construction details are not well resolved, leaving an element of the facade or roof without continuity in the insulation.

In a conventional dwelling, such an error might be acceptable if the rest of the building is well insulated. However, when dealing with a house intended to minimize energy loss as much as possible, we cannot allow any thermal bridge, as energy simulation models have shown that a small discontinuity can have a significant effect on the overall indoor environment.

In addition, a thermal bridge is a source of damp, as it is a cold point on a warm surface. This causes indoor humidity to condense in that area, creating hazardous damp and mould that is often not visible to the user.

Window quality

Similarly, windows represent points with a risk of energy loss, which could jeopardize the proper functioning of our Passivhaus home.

Investing in windows that ensure good airtightness and insulation is one of the premises for understanding how a Passivhaus home works.

In the design of a Passivhaus home, it is recommended to use double-glazed windows with a low-emissivity chamber or triple-glazed windows. These windows ensure the necessary insulating capacity, although we can always increase thermal performance to achieve more insulation. Not only is the glass important, but the joinery element must also feature a thermal bridge break system and insulating capacity.

Thermal Mass

Thermal inertia is the ability of a material to store heat and release it when the external environment is colder. This characteristic allows for capturing heat during the day—through solar radiation—and releasing it at night when the environment is cooler and there is a need to heat the dwelling. This is typically achieved through thick walls without a thermal insulation layer to allow heat to be stored and dissipated when the environment cools.

Airtightness

When explaining how a Passivhaus home works, we mention that besides having minimal consumption, the house must ensure minimal energy exchange with the exterior while respecting a maximum number of air changes per hour.

It is essential both for the dwelling and for the health of its inhabitants that a house renews its indoor air, but at the same time, it must be relatively airtight to avoid air leaks that could alter the indoor temperature of the rooms.

The Passivhaus seal is strict in this regard and requires ensuring that this minimum condition for air changes per hour is respected.

While the design of a Passivhaus home is completely airtight—they are known as “thermos houses”—renewal is guaranteed through a heat recovery ventilator to ensure good air quality without the need to open any windows. This point is currently being widely debated, as it is possible to ensure an indoor environment at the appropriate temperature without the need to turn our house into an airtight box where no outside air enters unless it is through a forced renewal system.

In practice, many passive houses operate with systems that do not rely on heat exchangers, achieving very positive results with nearly zero consumption through renewable energy systems and without active consumption.