Window pane condensation and high indoor vapour contribution - markers of an unhealthy indoor climate?

Objective The aim of this study was to investigate whether window pane cond ensation and indoor vapour contribution greater than or equal to 3 g/m(3) c ould be used as indicators of defective air change rate, high indoor humidi ty and high mite allergen concentration in mattress dust. Methods Actual ventilation rate, indoor temperature, air humidity (AIH/RH) and concentrations of mite allergen were measured in 59 houses and compared with received outdoor temperatures and air humidity. Indoor vapour contrib ution defined as the difference between the indoor and the outdoor vapour c oncentration was calculated. Sensitivity, specificity, predictive values an d accuracy were calculated for window pane condensation and high vapour con tribution (greater than or equal to 3 g/m(3)), as indicators of defective v entilation (< 0.5 ACH), high indoor humidity (greater than or equal to 7 g/ kg and greater than or equal to 45% RH) and high mite allergen concentratio n in mattress dust (greater than or equal to 2 mu g/g). Results All houses with high humidity and high mite allergen concentrations were positive for the two indicators (high sensitivity), but with a specif icity of only 50% so that half of the houses with reported condensation and high vapour contribution turned out to be low pollution houses with adequa te high ventilation levels. Both indicators had high negative predictive va lues and absence of the two indicators almost certainly (97-100%) excluded high indoor pollution with high humidity and high mite concentrations. Over all more than 70% of the dwellings were correctly classified by the two ind icators. Conclusion Absence of window pane condensation on double-glazed windows and low indoor vapour contribution (<3 g/m3) during the winter are true marker s of a dwelling without high indoor air humidity and without high mite alle rgen concentrations in mattress dust in houses in a cold temperate climate with subzero outdoor temperatures. The presence of the two indicators is as sociated with a 18-45% risk of high humidity and mite allergen concentratio ns so in this latter group further measurements are needed for correct clas sification.