The 2018 census gives insight into the extent of the mould problem in New Zealand housing.

In 2018, the Census dwelling form asked households for the first time whether or not any part of their dwelling was affected by mould at least A4 in size.  If the answer was yes, then Census dwelling respondents were able to indicate if the mould was always present or only sometimes present.  This question was added along with a question on dwelling dampness, in order to examine the quality of household’s dwellings across the country.

Overall, out of a total of 1,653,792 households, 64,386 households always had mould (four percent of total households), while a further 187,875 household sometimes had mould (11 percent of total households).

Examining the number of households with mould (either always or sometimes) across the 16 regions of New Zealand, highlighted that the regions with the largest share of mouldy households were in the North Island. Northland (20 percent of total household) and Auckland (19 percent of total households) regions lead the way, with Gisborne (18 percent of total households) and Taranaki (17 percent of total households) following just behind. At the same time all regions within the South Island of New Zealand had below average number of households with mould, with Marlborough the lowest region with just eight percent of households with mould issues.

Does it matter where you live in the country? Or if you own or rent your home?

Exploring the differences between the North and South Island, we examined the share of households that are either owner-occupied (including owned by a trust), or rented that are afflicted by mould.  The aim of this analysis was to determine if the mould issues were common across the regions and different household tenure categories, or if there was a clear regional or household tenure imbalance.    
As shown in the graph below, it is clear across the regions, as for New Zealand overall, that a larger proportion of rented household have mould issues, then owner-occupied households.  For New Zealand overall 11 percent of owner-occupied households had mould, while 23 percent of rented households had mould.

Northland had the largest proportion of households afflicted by mould issues, with 16 percent of owner-occupiers, and 28 percent of rented households.  At the other end of the scale Marlborough had the lowest proportion of households with mould across both owner-occupier (seven percent) and rented households (14 percent).  

Meaning that out of the 252,261 households in the 2018 Census with mould issues, 134,464 households were rented. It will be interesting to see if it is reduced by the Government healthy rental homes standards that came into effect on 1 July 2019. We will have to wait for the 2023 Census to measure the impact.  Of course the healthy homes standard only affects rented dwellings, so the 115,971 owner-occupied households with mould issues will just need to fix the underlying issues in their own dwellings.

Does it matter what heating system you use?

Further, we investigated if types of heating makes a difference in households with mould issues. Our analysis focused on the proportion of households with mould issues, amongst the nine most prevalent types of heating identified in the 2018 Census.  These nine types of heating cover almost three-quarters of total households.  Again the aim of this analysis was to see if mould issues were similar across different heating types or if there was a clear imbalance between the heating types that could be examined in more depth.   

The graph below shows the percentage share of total households per heating type , and the proportion of households using this heating option that have mould issues.  The analysis shows that households with only portable gas heaters have the highest proportion of households with mould issues at 29 percent.  This is followed by households with no heating options with 25 percent of their households with mould issues, and then households with only electric heating only with 24 percent.  Interestingly while only two percent of households have only a portable gas heater, and four percent have no heating options, 14 percent have only electric heating, which makes it the second most common heating option after heat pump only (18 percent of households).

At the other end of the spectrum, houses with heat pumps or fixed gas heater only, heat pump and electric heater, or heat pump and wood burner, had less than 15 percent of their households with mould issues.  Interestingly, according to BRANZ around 15 years ago only about four percent of houses had a heat pump, while by 2016 just over half of all new builds had a heat pump.  Also, Statistics NZ only expanded the types of heating category to include heat pumps for the 2018 Census, previously in the 2013 Census, heat pumps were included under electrical heating.  

Further work will be needed to fully understand the factors that influence which households are more prevalent to mould.