Introduction

Abstract

The thermal performance of the building envelope is central to the debate on the construction of “nearly zero energy buildings” (NZEB). The relationship between type of envelope and final energy consumptions is usually translated into a simplistic deduction: to ensure that the energy consumption of a building is close to zero, it is primarily necessary to dissipate very low heat during the cold season. A global building thermal resistance and airtightness is one of the most important prerequisites to achieve “nearly zero energy”. However, poorly permeable buildings are more subject to high internal moisture load in combination with an unsuitable ventilation strategy. Modern exterior insulation finish systems do not have thermal inertia and are therefore more subject to considerable amounts of exterior condensation. Moisture loads and surface condensations are favourable conditions for the proliferation of microorganisms, such as algae and fungi. Consequently, despite the fact that over the last decades building energy efficiency has improved and better quality in living spaces is required, the number of reports on the presence of microorganisms on building facades and indoors is still increasing.