House characteristics and indoor dampness and mould in three New Zealand House Condition Surveys conducted in 2005, 2010 and 2015 : a thesis by publications presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Wellington, New Zealand
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2023
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Massey University
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Indoor dampness is a common exposure associated with adverse health effects such as asthma and respiratory infections. This thesis aimed to improve understanding of the determinants of indoor dampness by analysing three New Zealand House Condition Surveys. The methodology included assessing associations between house characteristics and five assessments of indoor dampness (inspector-assessed subjective dampness, visible mould, musty odour and moisture measured in ceiling and floor joists). Using multivariate regression, the analyses showed that better insulation and ventilation were associated with less indoor subjective dampness, visible mould and musty odour, but were not associated with moisture measurements. Rental tenure and higher occupancy were associated with more subjective indoor dampness, visible mould and musty odour, and no associations were observed with moisture measurements. Poorer conditions of the subfloor (insufficient ventilation, absence of a ground vapour barrier and evidence of ponding or leaks) were associated with more subjective indoor dampness and higher moisture measured in the floor joists. Poorer condition, cumulatively, of five elements of the building envelope (condition of: roof, cladding, windows, exterior paint and spouting and guttering) was associated, in a dose-dependent manner, with more subjective indoor dampness, visible mould (including when restricted to bedrooms and living rooms only), musty odour and higher measured moisture in floor joists. Moisture in ceilings and floor joists were weakly correlated with each other, and with subjective dampness and musty odour, but moisture in joists was not associated with visible mould. The main conclusion is that the building envelope condition is an important determinant of indoor dampness. Also, the results described in this thesis strongly suggest that a single measure of indoor dampness may not fully capture the most relevant exposure; as a consequence, for future epidemiological studies on the health effects of indoor dampness, it may be best to collect (and analyse) several measures of indoor dampness.