Dampness is a problem in many homes. It’s a particular problem in rentals.
According to 2023 Census data, rental households were more than twice as likely as owner-occupied households to report dampness.
That’s bad news for health as mould and dust mites thrive in damp conditions, and can lead to people suffering allergies, asthma and severe respiratory illnesses.
Here's how you can reduce dampness and improve ventilation to make your home warmer and healthier. Drier houses are also easier to heat, so by fixing dampness you may pay less on your power bill.
Where does dampness come from?
Moisture build-up in the home isn’t just caused by rainy days and leaky roofs – our day-to-day living contributes too. Washing, cooking and even breathing all add moisture to the air.
Here are some common sources of moisture in your home.
Cooking: 3.0L per day.
Clothes washing: 0.5L per day.
Showers and baths: 1.5L per day (per person).
Washing dishes: 1.0L per day.
Clothes drying: 5.0L per load.
Gas heater (no flue): up to 1.0L per hour.
Breathing, active: 0.2L per hour (per person).
Breathing, asleep: 0.02L per hour (per person).
Perspiration: 0.03L per hour.
If you want to check the humidity in your house, consider buying a hygrometer, which measures temperature and relative humidity. You can pick one up for less than $20.
How to reduce the amount of dampness in your home
There’s no quick fix for tackling moisture. You need to identify where the dampness is coming from and try to stop or minimise it as best you can.
Keep rooms ventilated and warm during winter. Install curtains and draw them at night.
Always use close-fitting lids on pots when cooking and extractor fans over the cooktop or stove, and in the bathroom (these must be ducted to the outside).
Wipe off any water that has collected on the walls and on the inside of windows. You can consider buying a scoopy which collects condensation from surfaces.
Don’t use portable gas heaters without a flue inside. They make the air damp and also fill the air with dangerous gases. Use safer and cheaper-to-run electric heaters.
Install a showerdome. Showerdomes collect condensation from the shower, then send it down the drain. They are best fitted by a professional. If you rent, your landlord will need to OK the installation.
Use a cupboard heater in problem wardrobes.
Don't hang clothes inside to dry and if you have a vented dryer, make sure it vents outside.
Check the ground under your home is dry. Check drainage systems are diverting water away from the house. If the ground is wet, talk to your landlord about covering the ground with polythene (if feasible), fixing any leaks under the home and upgrading drainage.
Check for leaks and rot in the roof or around windows. If there are any, let your landlord know – they’re responsible for home maintenance.
Remove excess water from the air with a dehumidifier, or if you have a heat pump, it may have a dry mode. Find the best dehumidifier for your home with our buying guide and test results.
How to improve ventilation in your home
Ventilation helps remove moisture and airborne pollutants from the home. Older homes, which are often draughty, usually have fairly good natural ventilation. Newer houses are often fairly airtight, so require more conscientious airing.
Air your home once or twice a day. Opening a door or window at both ends of the house for 10-15 minutes creates a cross-draught that pushes air through more effectively.
Use extractor fans in bathrooms. Leave them on for a few minutes after you’ve finished showering or bathing to remove as much steam as possible (if there isn’t one, open the window).
Use extractor fans and rangehoods when cooking. Having a window open while cooking can also help.
Some rentals have ventilation systems installed. If you have one, ask your landlord how to use it properly – the settings can be adjusted for different seasons and conditions. Your landlord is responsible for the system’s maintenance, such as changing air filters.
Also see our tips on managing mould.
Dehumidifiers: do you need one?
If you’re ventilating and heating your home properly, but it’s still damp, consider getting a dehumidifier. Here are our tips for getting the most out of a dehumidifier.
Empty it regularly.
Think about where it’s positioned – the more centrally located it is, the more moisture it will collect from the air.
Dehumidifiers work best with doors and windows shut. Make sure you’ve dealt with any draughts too.
Get the humidity right – aim for relative humidity of between 30% and 50%.
Vacuum first – dehumidifiers can spread dust particles and their filters, if they have them, can get clogged with dust.
Dehumidifiers can be expensive to run. Find out more about dehumidifier running costs.
Health New Zealand | Te Whatu Ora funded this article as part of its ongoing efforts to raise awareness about the importance of living in a warmer, healthier home.
A renter's guide to a warmer home
Our free guide provides advice and tips on what you can do to make your home warmer, cosier and cheaper to heat.
