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  Mould and damp

Mould is a key indicator of poor indoor environmental quality and has implications for occupant health, including links to asthma, respiratory infections and rheumatic fever. 

The House Condition Survey includes three different assessments of mould and damp made as part of the physical house inspection. These include: 

  • the degree to which the house felt damp or dry
  • whether or not the house smelt musty
  • whether mould was visible, and to what extent (all rooms assessed individually). 


The surveyors found 31% of rentals felt damp to some extent (‘a little damp’ to ‘damp throughout’). This is nearly three times the proportion of owner-occupied houses (11%) (Figure 13).

Assessment of dampness in houses.jpg 

Figure 13. Surveyors assessment of damp in the house [Source: BRANZ House Condition Survey 2015/16] 

Twice the proportion of rentals (12%) had a musty smell compared to owner-occupied houses (6%).  

Overall, mould was visible somewhere in the house in nearly half (49%) of all houses surveyed (Figure 14), breaking down to 44% of owner-occupied and 56% of rental properties. In most cases this was just specks of mould, but in over one quarter of rentals there were moderate or worse patches of mould. Mould was most commonly found in bathrooms.

Mould anywhere in the house.jpg 

Figure 14. Worst case of visible signs of mould anywhere in the house [Source: BRANZ House Condition Survey 2015/16]. 

The owned vs rented difference was greater when mould in bedrooms is considered – almost 30% of rentals had visible mould in bedrooms, compared to 18% in owner-occupied houses. 

Strong connections were found between the presence of mould and the presence (or absence) of insulation, heating and ventilation, and heating type.  

As also might be expected, mould levels were higher in houses that had poorer condition ratings and were considered less well maintained overall. For example, there was moderate to extensive mould in 44% of houses assessed as poorly maintained compared to just 7% in houses assessed as well maintained.

Housing condition
Ventilation and moisture control
Comparing 2015 results with 2010
2015 survey report and Warm, dry, healthy report

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