Investigation on moisture and indoor environment in eight Danish houses

SUMMARY: For many years focus has been on reducing the energy demand in buildings. In existing dwellings this is often done by tightening the building envelope e.g. by changing the windows. The tightening leaves the main part of the ventilation of the dwellings in the hands of the occupants as the dwellings then need to be ventilated actively either by natural or mechanical ventilation. Increased focus on energy reduction together with requirements for e.g. thermal comfort indoors may lead to reduced indoor air quality and moisture problems which in turn may cause mould problems. This paper describes an investigation of the indoor air quality, relative humidity and air change rate in eight Danish houses. The houses were selected as they are all having recurrent problems with condensation on the windows. The houses were built between 1930 and 2007. Some of them have been only slightly renovated where others have been renovated completely. Seven of the eight houses were naturally ventilated and one was equipped with mechanical ventilation system. In each house room air temperature, relative humidity, and CO2 concentration were measured in all primary rooms together with the outdoor climate conditions. The average air change rate in each of the houses was measured using passive tracer gas technique, the measurement period being one to two weeks. Based on the measurements the ventilation condition of the houses was compared to requirements in the Danish building regulations in terms of air change rate, to indoor air quality in terms of CO2 concentration, and to the use of the house in terms of the level of the relative humidity and indoor moisture excess. Furthermore, the moisture production in the houses was estimated and compared to values provided in the literature. A better indoor air quality and lower moisture excess were demonstrated in the houses ventilated according to the Danish building regulations than in houses not fulfilling the requirements. Though, the results showed large variations between the eight houses but also between the parameters examined.