The effects of damp and mould are felt in homes around New Zealand every winter. Photo / Getty Images
Anyone who’s lived through a New Zealand winter knows all too well the effect mould and damp can have on your home and health.
We’ve all heard and perhaps lived the horror stories: dark spots appearing on your ceiling, flat-pack furniture literally rotting away, that musty smell, mould appearing on your clothes and shoes, and even sickness or respiratory issues.
It’s a familiar issue for countless Kiwis living in not-so-healthy homes, particularly those who are living in an older home that’s not as mould-proof as it could be.
So, what exactly causes mould to grow inside our homes and can we prevent it?
Mould is a fungus that thrives in damp areas either inside or outside.
Dr Caroline Halley, a senior research fellow at the University of Otago’s School of Medicine and Health Sciences, explains that mould needs “something to grow on, a source of nutrients and a supply of moisture” to flourish.
“Since mould can grow on many substrates and can absorb nutrients from small quantities of dust, the most important and modifiable factor to reduce indoor mould is to control moisture,” Halley says. It can be difficult to do this in this country, she says, because our climate is so damp.
“New Zealand has a pretty bad residential mould and dampness problem,” she says.
Mould can appear in all sorts of colours, from green to grey, brown and red, or black and white, or as stains on smooth surfaces. It’s normal for small amounts to appear in our homes, but it can cause serious issues when left to grow, signalling there’s too much moisture in the air or perhaps even a leak somewhere.
The most common cause of mould is condensation created when warm, damp air from your kitchen or bathroom comes into contact with cold surfaces.
Mould doesn’t just damage your home, furniture and clothes – it can also harm your health.
It releases tiny, invisible spores into the air, which can cause serious health problems when you breathe them in. Elderly people, young children, and those with allergies or breathing problems are particularly at risk. Some mould spores can even be life-threatening when inhaled.
A study carried out by the University of Otago from 2010 to 2014 looked at 450 homes in Wellington, and found that high levels of visible mould, mould odour and leaks were all associated with new onset wheezing in young children.
“Most of the adverse health associations that have been found to be strongly associated with dampness and mould are respiratory – so that’s increased cough, wheeze, more respiratory infections, increased asthma symptoms, and worryingly, the development of asthma in young children,” says Halley.
According to Allergy NZ, all moulds can potentially cause health issues, especially if you have asthma or another respiratory condition.
Some people are even allergic to mould, causing their immune systems to react when coming into contact with it. The symptoms for a mould allergy are similar to cough and cold symptoms, as well as having itchy or watery eyes, nose and throat.
If you suspect you’ve got a mould allergy or infection, see your doctor.
There are all kinds of products on the supermarket shelf promising to kill the mould in your home, but the best way to get rid of it might be good old-fashioned white vinegar, according to an online home care resource from Kāinga Ora.
Don’t use it on surfaces you don’t want to risk discolouring, as white vinegar can cause bleaching.
Pour some white vinegar into a spray bottle and apply directly to mould, or wipe it on to the surface with a clean cloth. To avoid damaging the paint on your walls or windowsills, you can dilute the vinegar with an equal amount of water and leave it on the surface for a few days. Wipe off the mould with a clean cloth soaked in soap and water.
Either wash or throw away the cloth when you’ve finished to avoid spreading the mould.
So, we know how to get rid of it – but how do we stop mould from growing in the first place? The key is to heat and ventilate our homes properly.
“Even ventilating for 10 minutes a day can help us reduce that build-up of moisture, especially if we can do this when our houses are warm,” Halley says.
“We need to make sure we also ventilate when we’re carrying out household activities that can generate moisture, such as using extractor fans when we are showering or cooking, using a clothes dryer or not drying our clothes inside without ventilating, not using unflued gas heaters.
“Making sure we fix up leaks as soon as we can and also making our houses easier to heat by installing insulation can also help. If mould is building up in your home, try to remove it frequently, particularly in bedrooms where we spend a lot of our time.”
All rental homes in New Zealand must comply with Healthy Homes Standards, which became law in 2019, with a final key compliance deadline of July 2025.
That means your landlord must make sure your home meets minimum requirements across five areas:
Heating: Your living room must have a fixed heating device that can achieve a minimum temperature of 18C
Insulation: Ceiling and underfloor insulation must meet the 2008 building code, or be at least 120mm thick
Ventilation: Your home must have openable windows in the living room, dining room, kitchen and bedrooms, and an extractor fan in rooms with a bath, shower or cooktop
Moisture ingress and drainage: There must be efficient drainage, guttering, downpipes and drains, with a moisture barrier like plastic sheeting between the ground and subfloor installed where possible
Draught stopping: Landlords must block gaps larger than 3mm in walls, ceilings, floors and windows. Open fireplaces must be blocked or sealed.
Your tenancy agreement should include an up-to-date, signed healthy homes standards compliance statement.
If you’re a tenant and feel your home doesn’t meet the required standards, you should first talk to your landlord and ask them to remedy the issues. If you can’t come to an agreement on getting the home up to standard or your landlord doesn’t take action in a reasonable time, you can apply to the Tenancy Tribunal for a remedy. Citizens Advice Bureau provides more information on your rights and how to address a non-compliant home.
A full checklist for tenants and landlords is available at tenancy.govt.nz/healthy-homes
This story was originally published in July 2023 and has been updated.
Bethany Reitsma is an Auckland-based journalist covering lifestyle and entertainment stories who joined the Herald in 2019.