1: Introduction

Mould is commonly overlooked and often taken for granted due to its abundance. Over 50% of all homes, new and old, contain mould and there is unfortunately very little accessible knowledge available of its devastating connection to health implications in New Zealand. Online research however shows the USA has documented medical history leading to black mould being listed as a Class 2 Biohazard alongside Asbestos. This illustrates the importance of why we should be treating black mould with the respect it deserves.

Several common mould species found in New Zealand are potentially highly toxic causing incurable respiratory diseases. Other commonly found species can be highly allergenic triggering chronic illness with regular flu-like symptoms. Asthmatics, children and the elderly are particularly susceptible.

Looking back at the history of New Zealand housing, it is now clear that we have become victims of building to a minimum standard. In hindsight it seems we have traded affordability for our health.

There were over 400,000 homes built in the 1970’s – 1980’s with the majority being uninsulated up to 1978 when insulation became mandatory. Very few of the homes which were insulated would be compliant now and yet we still live in them as they are. These homes are at a higher health risk.


2: What causes mould and why is New Zealand in particular so
badly affected?

There are three common causes of mould including condensation from lack of ventilation, plumbing leaks and external wall or roof leaks
Unfortunately, the building standards in New Zealand over the last three decades have contributed largely to a huge increase in all three of these categories to both residential and commercial sectors.

  • Condensation from lack of ventilation: Condensation is a huge problem in New Zealand with old houses and alarmingly new homes too. The USA, Canada, UK and most of Europe have made passive roof ventilation mandatory for several decades due to previous similar condensation mould issues. Since the early eighties, while the majority of the civilised world had amended the problem, New Zealand unfortunately completely overlooked ventilation whilst focussing heavily on weather tightness. To this day we are still building unventilated homes and until the NZ Building Code makes passive roof ventilation mandatory, our homes will continue to suffer. For further information on passive roof ventilation: www.vent.nz
  • Plumbing leaks: Throughout the late 70’s and 80’s, Dux Quest plumbing was introduced which was a revelation in NZ at the time with black plastic pipe replacing copper. It was a cleaner and quicker process and employed by thousands of plumbers across the country. However its lifespan was massively underestimated and the product was finally withdrawn around 1987 due to regular structural failure. Today most insurance policies will not cover repeat Dux Quest plumbing leak claims as the volume of damage has been so substantial. Consequently there have been, and will be thousands more undetected gradual leaks in NZ buildings providing a continuous moisture source for mould in cavities. Wall cavities are a perfect environment for the toxic mould species (Stachybotrys) which is now extremely common in NZ and has certainly been assisted by the failings of Dux Quest plumbing.
  • External wall or roof leaks: External leaks are a major contributing factor for water ingress and mould. Again, minimal construction standards are partially to blame leading to the approval of direct fix cladding which has since become responsible for what is commonly known as ‘Leaky Buildings’. New Zealand has been exposed to affordable cladding systems which have failed on a national scale. We live in a seismic country with continual ground movement and yet we have utilised non-flexible, thin, cementitious wall sheet products which crack and leak. Different plaster systems have also been utilised and failed. Directly fixed cladding to the timber framework of a building without a drained cavity is a predominant contributor to water ingress and mould in our external wall cavities.

The residential housing market has a huge mould problem which is partly due to building to minimum requirement and also by the way we live. Humidity in our homes is created by tumble driers, unventilated gas fires, cooking, towel radiators, showers, baths and simply breathing. In an unventilated and sealed living environment, the humidity will rise into the roof void where it is trapped in a weather tight space. During the colder months, this warm humid air will condense, generally on the underside of the roofing paper/membrane which is the greatest point of temperature differential. This is called the ‘Dew-point’. The condensation will commonly run down the underside of the roof membrane and soak into the roof insulation at eaves. This is the perfect environment for mould growth which will filter through the ceiling lining and enter the habitable environment.