A striking example of the consequences of poor ventilation and moisture control emerged recently in Wellington, where an abandoned home became home to an industrial-sized puffball of mould. The overgrown fungal growth drew attention not just for its size but for the severe health and safety risks associated with unchecked indoor mould.
The 1980s Khandallah home has neighbours complaining of a strong smell on the street, spores settling in properties nearby, and the eyesore the abandoned building has become. They are also concerned that the property is bringing crime into the area; it’s been burgled many times now.
Cases like this highlight the importance of proactive moisture management, adequate ventilation, and regular maintenance in New Zealand homes. With a damp, temperate climate and building practices that sometimes fail to manage moisture effectively, mould remains a persistent challenge nationwide.
Preventing mould starts with controlling indoor humidity, maintaining airflow, and addressing cold surfaces where condensation can occur. When mould appears, prompt and effective remediation is essential to protect both occupant health and building integrity.
New Zealand’s climate and housing characteristics create ideal conditions for mould growth. Many homes experience high relative humidity and frequent rainfall, particularly in coastal and low-lying regions. Warm indoor air contacting cold surfaces, such as single-glazed windows, uninsulated aluminium frames, or poorly insulated walls, leads to condensation—a key contributor to mould proliferation.
Poor ventilation exacerbates the problem. Many homes lack adequate airflow in areas such as wet rooms, kitchens, bathrooms, and laundries, allowing moisture to accumulate and potentially cause damage. Everyday activities such as cooking, showering, or drying clothes indoors increase indoor humidity. Furthermore, building design issues like thermal bridging, inadequate insulation, or moisture traps behind furniture and fixtures create additional risk zones.
Mould spores are present in virtually every home. Still, these environmental and design factors enable them to settle, multiply, and become visible on surfaces such as walls, ceilings, cupboards, carpets, and even behind wardrobes. Without proper intervention, small patches can rapidly expand, posing a threat to structural components and interior finishes.
Preventing mould is fundamentally about controlling moisture sources and ensuring proper airflow. Modern building design and renovation practices in New Zealand increasingly incorporate the following strategies:
· Ventilation: Ensure that wet areas such as kitchens, bathrooms, and laundries have functional windows and exhaust fans. Mechanical ventilation systems, including heat recovery ventilators (HRVs) or demand-controlled ventilation systems (DVS), can maintain optimal airflow even in tightly sealed homes. Regularly opening windows and doors to flush humid air remains an effective, low-cost strategy.
· Heating: Maintaining indoor temperatures at or above 18°C reduces condensation on cold surfaces. Consistent heating prevents areas from cooling excessively overnight or during wet periods.
· Thermal barriers and insulation: Installing vapour barriers under floors, insulating walls and ceilings, and designing for thermally broken window frames with double or triple glazing reduces cold surfaces where moisture condenses. Minimising thermal bridging is essential, particularly around window frames, floor junctions, and roof lines.
· Immediate water management: Fix leaks promptly, address plumbing issues, and manage household moisture activities, such as wiping condensation from windows and avoiding indoor clothes drying without ventilation.
· Clear airflow: Avoid placing furniture directly against walls, keep wardrobes and cupboards ventilated, and prevent mattresses from lying directly on cold floors to reduce hidden damp zones.
These strategies are most effective when paired with resident awareness, ensuring that occupants understand the importance of ventilation, heating, and regular maintenance.
Mould is more than an aesthetic problem—it can pose serious health risks. Common mould species produce spores that can exacerbate respiratory conditions, trigger allergies, or cause chronic irritation. Toxic mould species such as Stachybotrys chartarum (black mould), though less common, require professional intervention due to their higher risk profile.
Studies indicate that roughly half of New Zealand homes have some level of mould contamination. Vulnerable populations, including children, the elderly, and those with pre-existing respiratory conditions, are particularly at risk. Symptoms associated with exposure include coughing, wheezing, eye irritation, and, in severe cases, long-term respiratory issues. By reducing mould exposure, homeowners can significantly improve their indoor air quality and overall well-being.
When mould is present, addressing it safely and effectively is crucial:
· Identify and eliminate the source of moisture before cleaning; otherwise, mould will return.
· Small patches can often be treated with detergent solutions, followed by thorough drying.
· Larger infestations, or those involving suspected toxic mould, require professional remediation to remove affected materials safely.
· Porous materials, such as plasterboard or insulation, that are heavily contaminated should be removed and replaced.
· Post-remediation, maintain humidity control and ventilation to prevent recurrence.
Several organisations provide guidance on mould prevention and remediation in New Zealand. MBIE, BRANZ, and Building Performance New Zealand recommend building and renovation practices that minimise moisture accumulation. Compliance with the New Zealand Building Code, particularly clauses addressing moisture (E2) and ventilation (G4), is increasingly enforced. Public health agencies also promote awareness campaigns on the dangers of mould, especially in rental housing and older homes prone to dampness.
The Wellington puffball case illustrates the extreme end of a spectrum of mould-related challenges in New Zealand. Prevention, through measures such as moisture control, ventilation, insulation, and heating, is far more effective than remediation alone. For homes that develop mould, safe and prompt removal is essential to protect both occupants and building structures. Homeowners, builders, and policymakers must prioritise integrated moisture management, educational initiatives, and robust building practices to ensure healthier indoor environments. By addressing the root causes of mould, New Zealand can reduce health risks and safeguard the longevity of its housing stock.
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