Comparison of two-level and three-level classifications of moisture-damaged dwellings in relation to health effects

A total of 630 randomly selected dwellings were surveyed for visible signs of moisture damage by civil engineers, and questionnaire responses were collected from the occupants (a total of 1,017 adults) to analyse the association between moisture damage and occupant health. A three-level grading system was developed, which took into account the number of damage sites in buildings and estimated the severity of the damage. In the present study, this grading system was tested as an improved model of moisture damage-related exposure in comparison to a conventional two-category system: based on independent, technical criteria it also allowed dose-response to be estimated. The questionnaire probed 28 individual health symptoms, based on earlier reported associations with building moisture and mould-related exposure. Criteria in evaluating the goodness of the selected exposure model were (1) dose-responsiveness and (2) higher risk compared to a two-level classification. Dose-responsiveness was observed with the three-level classification in 7, higher risk in 10, and both criteria in 5 out of 28 health symptoms. Two-level classification had higher risk in 4 health symptoms. Dose-dependent risk increases for respiratory infections and lower respiratory symptoms, and recurrent irritative and skin symptoms were observed with the three-level classification using symptom score variables. Although the results did not unambiguously support the three-level model, they underline the importance of developing more accurate exposure models in assessing the severity of moisture damage.