Nearly Zero Energy Buildings and Proliferation of Microorganisms

Abstract

In recent building practice, obligations to legislation on energy saving are carried out mainly by a high thermal resistance and a global airtightness of the envelope, aiming to minimise heat dispersions by conduction and infiltration as much as possible. These measures determine new ways of heat and moisture exchange in the building envelope and are likely to exacerbate the growth of microorganisms. New poorly permeable buildings are in fact more subject to high internal moisture load, in combination with an unsuitable ventilation strategy. Modern exterior insulation finish systems do not have much thermal inertia and are more subject to undercooling phenomena, condensation and a consequent higher biological growth risk. Renovation techniques, such as the replacement of single glazed windows by new very tight double or triple glazed windows or the addition of interior insulation, induce condensation phenomena on the unavoidable thermal bridges (frames, subframes, structure). The NZEB of the future must be able to give a concrete answer to these problems, since, although no changes occur in the thermal performance of the buildings, biological defacement has an enormous aesthetic, health and economic impact, which gathers the disapproval of building’s dwellers. This chapter will explore these topics, by describing the major consequences of the ‘sealing action’ and ‘overinsulation’ on the proliferation of microorganisms in NZEB.