Blower Door Test for Passivhaus Certification

In recent days we have carried out two Blower Door tests in a Passivhaus-certified house that we currently have underway at the studio.

A Blower Door is an air-tightness test that makes it possible to detect leaks in the building. It is a mandatory test to certify a Passivhaus house and is recommended for all passive houses, even if certification is not intended.

The test consists of artificially modifying the pressure conditions of a space, building, or home to study its behaviour. In this way, it measures uncontrolled air infiltration so that sealing defects can be addressed.

Leaks, which are usually found at joints and junctions between materials, compromise a building’s airtightness, reducing its energy efficiency. That is why achieving airtightness is one of the secrets to energy savings in passive houses and therefore one of the key aspects of their construction.

The lack of air exchange with the outside sometimes surprises many clients who think the indoor air will become stale, but in passive houses a renewal of indoor air is always ensured. In fact, this is mandatory under building regulations and is usually carried out through mechanical ventilation 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 of air renewal is ensuring that the outdoor air introduced does not enter at the outdoor ambient temperature, but that there are ways to preheat it. In other words, if it is 2°C outside, we can preheat this air, for example, through a greenhouse or a Canadian well (earth tube) that runs underground, so that fresh air enters the home at a temperature of around 20–22°C.

Thanks to the Blower Door test, it is possible to identify construction weaknesses, reduce energy costs, improve comfort by avoiding draughts, reduce noise from outside, and prevent the possible appearance of fungi or mould.

To certify a Passivhaus house, it is necessary to carry out at least one test at the end of the works, achieving results below 0.6 r/h, air volume changes per hour. This result corresponds to the building’s air permeability parameter known as n50, which is calculated by dividing the volume of air that infiltrates or escapes by the total air volume. Thus, the greater the air leakage, the higher the result and therefore the worse the home’s airtightness.

According to Passivhaus certification criteria, it is essential to carry out a test once the works have been completed. In this case, as we are working with different contractors, we have decided to carry out a preliminary test during the construction phase to ensure that each participating company assumes responsibility and corrects any possible execution errors in advance.

The test consisted of a two-day process, so that anomalies were detected and could be corrected between the two tests.

The test is carried out with a fan installed in the access door using an adjustable frame, applying a constant pressure of 50 Pa. First, the home’s natural air inlets, such as chimneys, are sealed, and doors and windows are closed.

On the first day, air is extracted from the house to the outside to force air to enter indoors, thereby detecting its entry points. By bringing a candle close to the joints, we can detect even the slightest draughts. This check can also be carried out with a thermal imaging camera.

Next, we reverse the direction of the fan and introduce air to create overpressure in order to detect leaks to the outside. These leaks become visible from the outside with the help of a smoke-generating machine.

In both tests, the same pressure of 50 Pa is applied, so the overpressure and underpressure results must match to confirm that the test has been carried out correctly.

The first day ends with results above what is desired, which is normal at a preliminary stage. So joint sealing begins using different methods, and the test is repeated a week later, again checking underpressure and overpressure.

After this second test, the result obtained is 0.359 r/h, below the 0.6 r/h required for certification—an excellent result, considering that we are still in the construction phase. Without a doubt, the success of the test is the result of teamwork by excellent, specialised, and committed professionals.