Airtight building envelope and dwelling ventilation in interrelation -retrospection and forecast for Switzerland

All times the building cover was made as airtight as possible. With massive constructions it was all above the plasterwork, which took over the sealing function. The air exchange was usually realised by the leaky windows, which still had no circular seals. With the usual massive constructions, built after 1945, the relative interieur air humidity was about 30 to 35%, the natural air change rate amounted tonL of about 0,3 to 0,5 per hour. Deep space air humidities prevent to a large extent the mold formation with thermic weak points in the construction; mites dessicate with deep relative humidity and are no longer active.After the oil shock in the beginning of the 70's it was realized that the unregulated air exchange is connected with large heat losses through the leaky windows. Under multimedia guidance in whole Switzerland the windows were sealed with foam material and rubber bands, with fatal consequences. The natural air change was drastically reduced. It usually decreased under 0.1 per hour, i.e. less than 1/10 of the air were replaced per hour. With constant dampness production inside the buildings the relative interieur air humidity rose to values over 50%; relative interieur air humidities over 70% were not a rarity. These high relative interieur air humidity led to mold in cold areas of the wall surface. This mold growth and rot again caused serious endangerment of the construction. The low air change also led to an increase of the concentration of indoor air pollutants. Particularly to mention are the human metabolites (CO2), tobacco smoke, formaldehyde, volatile organic compounds (VOC), radon, house dust etc. An inappropriate user behavior in individual cases still intensified the increase of the relative interieur air humidity. The frequently asserted allegation that the user alone was responsible for the high relative interieur air humidities, was not correct in most cases. Investigations showed, that such airtight buildings should briefly be ventilated each hour, in order to achieve a sufficient air change over the whole day. This is however hardly practicable, especially not with working people.