H. Preisig
Bibliographic info:
2nd European Blower Door Symposium, March 2007

All times the building cover was made as airtight as possible. With massiveconstructions 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 nocircular seals. With the usual massive constructions, built after 1945, the relativeinterieur 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 extentthe mold formation with thermic weak points in the construction; mites dessicate withdeep relative humidity and are no longer active.After the oil shock in the beginning of the 70's it was realized that the unregulated airexchange is connected with large heat losses through the leaky windows. Undermultimedia guidance in whole Switzerland the windows were sealed with foammaterial and rubber bands, with fatal consequences. The natural air change wasdrastically reduced. It usually decreased under 0.1 per hour, i.e. less than 1/10 of theair were replaced per hour. With constant dampness production inside the buildingsthe relative interieur air humidity rose to values over 50%; relative interieur airhumidities over 70% were not a rarity. These high relative interieur air humidity led tomold in cold areas of the wall surface. This mold growth and rot again caused seriousendangerment of the construction.The low air change also led to an increase of the concentration of indoor airpollutants. Particularly to mention are the human metabolites (CO2), tobacco smoke,formaldehyde, volatile organic compounds (VOC), radon, house dust etc.An unappropriate user behavior in individual cases still intensified the increase of therelative interieur air humidity. The frequently asserted allegation that the user alonewas responsible for the high relative interieur air humidities, was not correct in mostcases. Investigations showed, that such airtight buildings should briefly be ventilatedeach hour, in order to achieve a sufficient air change over the whole day. This ishowever hardly practicable, especially not with working people.