Why Christchurch Homes Get Mould, and What Actually Stops It

Surface mould in window reveals, black spotting on bathroom ceilings and a musty smell in the back bedroom are the most common winter complaints we hear in Christchurch.

It is not a cleanliness problem in the way people assume. Spotless homes get mould too. It is a moisture and temperature problem, and cleaning is only half the answer.

Understanding why it happens here makes it much easier to stop.

Why Christchurch is prone to it

Cold nights, still air and long heating seasons are the combination. Warm moist air inside meets a cold surface such as single glazing, an uninsulated wall or an unheated room, and it condenses. Mould needs moisture, a surface and mild temperatures, and a Christchurch winter provides all three daily.

Older housing stock makes it worse. Single glazing, limited underfloor insulation and unflued heating in some homes all add moisture or cold surfaces to the equation.

Where it appears first

Mould shows up in predictable places, and knowing them means you can check before it spreads.

• Window reveals and the bottom of the window frame
• Bathroom ceilings directly above the shower
• Silicone seals around baths, showers and basins
• Behind furniture pushed hard against an exterior wall
• Inside wardrobes on an exterior wall
• Curtain hems and the back of curtains

Removing it safely

Do not dry brush mould. That sends spores into the air and spreads it around the room. Wipe it with a damp cloth first.

For hard surfaces, a diluted bleach solution or a dedicated mould treatment works, applied with a cloth and left to sit rather than immediately scrubbed. Ventilate the room while you work and wear gloves.

On silicone, mould often grows into the seal rather than on it. If a treatment does not lift it, the silicone needs replacing, which is a maintenance job rather than a cleaning one.

Stopping it coming back

Removal without changing the conditions just resets the clock. These are the habits that actually hold it back through a Christchurch winter.

• Run the bathroom extractor fan during the shower and for twenty minutes afterwards
• Open windows for ten to fifteen minutes each morning, even in winter
• Dry washing outside or in a vented dryer, never on an airer in a closed room
• Use lids on pots and the rangehood while cooking
• Keep furniture a few centimetres off exterior walls so air can move
• Heat the house steadily rather than in short bursts
• Wipe condensation off window sills in the morning before it soaks in

When it is the landlord's responsibility

If you are renting and mould keeps returning after cleaning, the cause is usually the building rather than the household. New Zealand's Healthy Homes standards cover heating, insulation, ventilation, moisture ingress and draught stopping.

Report it in writing, with photos and dates. A pattern of reports protects you at the next inspection and puts the responsibility where it belongs.

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