Condition of the building envelope is associated with indoor dampness, mould and musty odour, as well as moisture measured in floor joists

Interventions designed to reduced indoor dampness and mould have shown mixed results, suggesting that the causes of indoor dampness are not yet fully elucidated. Poor repair and infrequent maintenance have been demonstrated to be associated with indoor dampness and mould in several previous studies, as has age of the building, however these associations do not easily translate into specific interventions other than generally improving condition or maintenance of buildings. Using regression analysis in three New Zealand house condition surveys, the author demonstrated that the condition of five specific components of the building envelope (roof, windows, wall claddings, spouting and guttering and exterior paint) are associated, with a dose-dependent effect, to increased risk of indoor dampness, visible mould, musty odour and moisture measured in floor joists. It is also demonstrated that musty odour is strongly associated with subfloor defects (absence of sufficient ventilation, ponding or leaks and lack of a ground vapour barrier)

The causes of indoor dampness and mould are multi-factorial, and although some are well understood, for example poor ventilation and high occupancy, other evidence suggests that gaps in the understanding remain [1,2].Furthermore, there is little evidence that prevalence of the exposure has significantly reduced over time [3].Numerous house characteristics have been assessed in relation to indoor dampness and mould, and this evidence suggests that specific characteristics can be important determinants of indoor dampness and mould [4][5][6][7][8][9].Several studies have reported associations between housing in poor repair and indoor dampness and mould [10][11][12].However none of these studies have further broken down this poor repair rating into the repair or condition of specific components.In this study, data from three New Zealand house condition surveys conducted in 2005, 2010 and 2015, was pooled, and associations between house characteristics and five measures building dampness were assessed.All house characteristics and dampness measures were assessed by experienced house inspectors.Visible mould was assessed by room.Here we aggregated in two different ways, using mould reported anywhere in the house (Mould whole house) and only mould reported in living or bedrooms (mould living and bed).Dampness was assessed once only per house, as a subjective sensation of dampness, and musty odour likewise assessed only once per house by inspectors.
Data on outdoor temperature and rainfall in the thirty days previous to the inspection were downloaded from the weather station closest to each house (distance to house on average <10km).This data was tested at increments of 3, 7, 14, 21 and 30 days, and the 30 day data was most strongly associated with moisture outcomes.Houses were assigned to climate zones based on those identified in the New Zealand Building Code, defining regions of higher and lower insulation requirements, with three climate zones included.
Using multivariate logistic regression for visible mould, subjective dampness and musty odours (as dichotomous outcomes) and linear regression for moisture measured in floor and ceiling joists, a multivariate model was fitted using aggregated domains.The following domains were included: Insulation; presence of ceiling, wall cavity and underfloor (for a total value for each house for between 0 and 3), Ventilation; presence of extract ventilation in kitchen, bathroom and clothes dryer (each house value from 0 to 3), Subfloor; absence of adequate ventilation, presence of ponding or leaks and absence of a ground vapour barrier (each house value between 0 and 3) and Building Envelope Condition (BEC); moderate, poor or serious condition of the roof, wall claddings, windows, spouting and guttering (combined) and exterior paint (each house value from 0-5).
More insulation and extract ventilation were both associated with dose-dependent reduced likelihood of dampness, mould and musty odour, but were not associated with moisture in floor and ceiling joists (data not shown).The coldest (Southern) climate zone was associated with reduced likelihood of visible mould, but was not clearly associated with other moisture outcomes (data not shown).More aggregated subfloor defects were dose-dependently associated with musty odour indoors, and with subjective indoor dampness, but were also not associated with moisture measured in ceiling and floor joists (Table 1).More aggregated building envelope defects were associated dose-dependently with visible mould, musty odour and subjective indoor dampness (Table 1).A greater number of building envelope defects were also associated with increased measured moisture in floor and ceiling joists (Table 1).Since these analyses were adjusted for other known determinants of indoor dampness, including insulation, ventilation, occupancy and climate zone, our results demonstrate that external condition of houses is an important independent determinant of indoor dampness and mould.This study also demonstrates a strong association between conditions in the subfloor and musty odour, which is not present for visible mould.This may point to different types of indoor dampness having different causal pathways.

Table 1 .
Multivariate regression of the determinants of five house dampness measurements