Mastering building airtightness is essential to meet the requirements of current and future building codes, not only for saving energy but also for ensuring moisture safety. Perfect airtightness is difficult to achieve: failures are often observed, due to bad design or poor workmanship. Some published investigations proved that leaking air mostly flows through porous material and thin air channels, due to material imperfections and construction tolerances.

Since 2000, the French EP-calculations have been considering thermal losses due to building envelope airtightness. The last two regulations (RT2000 and RT2005) had included a default value for airtightness and the possibility to use a better-than-default value with a mandatory justification of this value, especially for voluntary approaches such as the BBC-Effinergie label. In 2013, strengthening the airtightness has become a requirement of the current EP-regulation (RT2012).

In 2014 the first multi storey residential building planned and constructed to meet the Passivhaus Institute (Darmstadt) criteria was put in operation in Ljubljana, the capital of Slovenia. This massive-structure building is part of the FP7 EE-Highrise project, aiming to demonstrate nearly zero energy building (nZEB) technologies, an integrated design concept, and advanced systems for sustainable construction.

Nowadays, there is increasing construction of high-rise buildings. Stack effect is one of the airflow characteristics in this type of tall buildings. The upward buoyant airflows in vertical shafts of high-rise residential (HRR) buildings can become an important way of gaseous pollutant transport during cold seasons. In this paper the airflows and pollutant transport driven by stack effect in a typical HRR building in Shanghai was simulated by using a multi-zone model. Measured and recommended leakage data were employed, and the air tightness level was kept the same for all floors.

Previous studies on single-sided natural ventilation are mostly limited to very simple physical models, such as a single-room or single-storey building. Our recent on-site measurements have shown that previous empirical models based on such simple physical models are inapplicable to multi-storey buildings. In order to explore why, this study systematically compares the ventilation characteristics of single-storey and multi-storey buildings with single-sided natural ventilation.

One of the most commonly used strategies to reduce the heating demand in low energy buildings is reducing the leakage level of the building envelope. Dedicated ventilation systems are then installed to compensate for the reduced air change rate in an energy efficient way. Most occupants, however, operate their ventilation system at very low flow rates. Together with the emission of bio-effluents, linked to the presence of the occupants, moisture production related to household activities is one of the most important sources of indoor air pollution in dwellings.