Criteria to define limits for building airtightness. Airtightness of some Portuguese dwellings

The increasing concern on energy conservation in buildings and the increasing insulation level of buildings, lead to the introduction of limits for building airtightness, to minimize building heat losses. In some countries the recommended limits are very strict and could be difficult achieved with standard construction practices. Usually the limits are established according construction (best) practices and in some countries it takes in account the building type, ventilation system and weather. Usually those limits dont take in account the air flow rate for background ventilation. In Portugal the concern about building airtightness is limited to air permeability of windows. In the study curried out it was assessed the importance of whole building airtightness, versus window air permeability and the importance of whole building airtightness to define limits that take in account, energy losses, indoor air quality and ventilation requirements and the action that promote the pressure difference across building envelope (wind actions, thermal buoyancy and ventilation systems).