airtightness

Mandatory or voluntary building airtightness testing has come gradually into force in many European countries mostly because of the increasing weight of building leakage energy impact on the overall energy performance of low-energy buildings. Therefore, airtightness levels of new buildings have significantly improved in the last decade, but a lot of questions remain regarding the durability of airtightness products.

The building airtightness is essential to achieve a high energy performance. In most countries however, it is not mandatory to measure the airtightness. In the Netherlands it is common practice to just take several samples in a housing project. These samples do not give a good indication for all the buildings in a project. It is therefore important to measure the airtightness of all the buildings. 

Upper floors of super-tall residential buildings have different characteristics of the exterior environment as compared to their low floors or low-rise residential buildings due to the high-rise. Upper floors are more affected by direct solar radiation due to the reduced number of adjacent shading buildings and by reflected solar radiation from rooftops. Super-tall buildings also have high level of airtightness because of higher wind speed with high-rise.

Between 2017 and 2018, the Centre for Studies and Expertise on Risks, the Environment, Mobility and Planning (Cerema) organized an airtightness measurement campaign in 117 multi-family collective and single-family French dwellings. These dwellings were built before 2005, that is, before the release in 2005 of the fifth French thermal regulation for new dwellings, that was the first to introduce specific requirements for airtightness.

Across different territories there are various normative models for assessing energy demand of domestic dwellings, which use simplified approaches to account for the heat loss due to the air infiltration of a building.  For instance, the United Kingdom uses a dwelling energy model, known as the Standard Assessment Procedure (SAP), and this utilises a process where the measured air permeability value (q50), is simply divided by 20 to provide an infiltration rate (subsequent modification factors are then used for factors such as sheltering etc.).

Buildings represent approximately 40% of global energy demand and heat loss induced by uncontrolled air leakage through the building fabric can represent up to one third of the heating load in a building. This leakage of air at ambient pressure levels, is known as air infiltration and can be measured by tracer gas means, however, the method is disruptive and invasive. Air infiltration models are a non-disruptive way to calculate predictive values for air infiltration in buildings.

Infiltration is an uncontrolled contribution to ventilation in a building and can contribute significantly to the total ventilation rate, particularly in older, leaky, dwellings which can rely on infiltration to provide adequate indoor air quality. However, as explored in this paper, using a whole house airtightness metric to characterise ventilation rates can fail to identify low ventilation rates in specific rooms. 

Mandatory or voluntary building airtightness testing has come gradually into force in many European countries mostly because of the increasing weight of building leakage energy impact on the overall energy performance of low-energy buildings. Therefore, airtightness levels of new buildings have significantly improved in the last decade. However, rather limited expertise is available as regards the durability of building airtightness at mid- and long-term scales.

Due to the wind induced pressure, different results may be obtained if the inside-outside pressure difference is measured across different locations on the building envelope, i.e. if the external pressure tap of a differential pressure sensor measuring this pressure difference is placed in different positions. Therefore, the position of the external pressure tap may influence an airtightness test result as well.