Passivhaus, in search of maximum energy efficiency

When we hear the word passivhaus, and that happens more and more frequently, we can get a more or less accurate idea of its meaning, which will undoubtedly lead us to a specific type of housing, without air leaks, with a good seal and, therefore, with low energy consumption.

Do we agree?

We are not wrong when we think on this way, but to fix concepts today we bring you this post about the passivhaus standard, its origin, its meaning and the main characteristics and objectives on which it is based.

Passivhaus Standard, what does it imply?

Passivhaus is a standard for building construction that aims to reduce energy consumption in the home.

The usual calculations show energy savings of up to 90% compared to older buildings and more than 75% for more recently constructed buildings.

To achieve this, a series of requirements and calculations on energy expenditure are taken into account, which we will see below.

The goal: limiting the energy demand to 15 kWh/m2 for heating and cooling.

Heat gains and losses by house type - Passivhaus vs others


The Passivhaus standard was born in 1988 between Bo Adamson, professor at the University of Lund in Sweden, and Wolfgang Feist, who was part of the German Institute for Housing and Environment in those years. During the first discussions they established the theoretical structure of passive houses.

From these first steps and thanks to financial assistance from the German state of Hesse, the passivhaus concept was developed through numerous studies and research projects.

The first houses were built in the city of Darmstadt, in the state of Hesse itself, and in 1996 the Passivhaus-Institut was founded.

Today, there are an estimated 25,000 passivhaus homes, mostly in Germany and Austria.

Basic Principles

In order to achieve the energy savings that will enable us to obtain a passivhaus certificate, some basic principles on orientation and insulation must be taken into account.

For example, regarding to the use of the sun, heat sources and their recovery, it is sought the use of passive cooling techniques, such as calculating the shade on the facades of the house, which contribute to keeping it cool.

Insulation, the thermal envelope

The insulation of the thermal envelope, which means all the enclosures that separate the house from the outside, such as floors, facades, roofs, etc., prevents heat from entering or leaving.

Its placement is crucial for the proper thermal functioning of the building.

Unlike conventional buildings, which usually use active systems to keep the heat in, in the case of passive houses the goal is to make the interior work as a thermos flask. To achieve this, the insulation layer must be continuous between all the elements that make up the building envelope.

Thermal envelope of a building

The thermal envelope covers all the enclosures that separate the dwelling from the outside

Removal of thermal bridges

If continuity in the insulation is not achieved, thermal bridges will occur at the meeting points between materials in the enclosure, which are a direct source of energy loss and dew points.

An example of a thermal bridge usually occurs in windows, which are the weakest areas of the enclosure. Insulating glass is a worse conductor than aluminium, which is why heat loss happens through the window’s frame.

To avoid these losses, the thermal bridge is use to be broken, avoiding contact between the exterior and interior faces by interspersing a material such as polyamide rods, which are a poor conductor and help to reduce energy loss.

Thermal bridges and heat map of a building

Thermal bridges occur at the meeting points between enclosure materials

Controlling infiltration

Air infiltrations into the house are necessary, but if these are not controlled, they result in excessive energy loss.

Within the passivhaus standard, the control of infiltrations is another key point. Through a structure of heat recovery, we manage to recycle the outgoing air, maintaining its temperature, and introduce, without mixing it with the previous one, fresh air.

A heat recuperator is a device that in winter works by heating the cold air that enters from the outside and in summer by cooling the hot air so that it reaches the interior of the house in a comfortable temperature.

As a device, it is basically a box with some ducts and filters that help the exchange of the exhaust air (the interior) with the supply air (the exterior).

Certified passive houses have an airtightness of 0.6 renewals/hour of the interior air, far from the 5/7 usual in conventional buildings

Heating recovering system for passivhaus

Con un sistema de recuperación de calor se recicla el aire interior regulando su temperatura

Characteristic requirements

Heating demand

It is probably the most important value, as it takes into account the balance between heat losses and gains.

If losses are represented by thermal bridges, leaks, air infiltration, etc., gains take into account everything from sunlight to internal heat sources such as appliances or people.

If the demand is limited to the 15 kWh/m2 we saw before, the house can be heated with great savings and with a simple ventilation and heat recovery system.

In contrast, for hot climates, the demand for cooling is taken into account, seeking to avoid excessive overheating that would make the comfort inside the home worse.

Blowerdoor sealing and testing

In order to know the watertightness of a house that, as we saw before in the case of the passivhaus, which should not exceed 0.6 renewals/hour of air, is usuarlly carried out a test called Blowerdoor.

This test consists of placing a fan that depressurizes the interior of the building and analyzes its airtightness, with the natural air inlets sealed.

The fan measures the pressure difference between the interior and the exterior and then produces a graph of air flow and pressure, while calculating the number of air renewals per hour.

With this test it is possible to identify the situation of air leaks, cracks in the roofs, the very tightness of networks and ducts, etc.

blowdoor test for measure the air leaks in a passivhaus

The Blowerdoor test is used to study the air flow in the home

La rehabilitación energética, la certificación “EnerPHit”

We could think that acquiring the passivhaus certificate is only possible for new construction and that, if your house is old or was built without following the requirements of the Passivhaus-Institut, it is impossible to improve its energy efficiency and acquire the corresponding certificate.

However, if a series of requirements, more lax than for the passivhaus standard, are achieved in a renovation, it can be certified as an EnerPHit home, also promoted by the Passivhaus-Institut.

The requirements for achieving EnerPHit certification include the following:

  • Energy demand of 25 kWh/m2
  • Total primary energy demand not exceeding 120 kWh/m2
  • Air renewals ≤1/hour

And so much for this post about the passivhaus standard. We hope it has served as an introduction and has given you ideas if you are considering building a house or rehabilitating or reforming an old property.

In our section of Rehabilitation and Renewal you will be able to see all the advantages related to the energy efficiency that supposes to use the STACBOND aluminium composite panel in reforms and rehabilitations.