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Tackling dampness

About 30% of our homes suffer from problems associated with being damp. Dehumidifiers and ventilation systems are used to fix the symptoms of the problem, but not the source of the problem itself. Dampness makes rooms unhealthy to live in. In a lot of cases though, it is also a problem that is relatively cheap and easy to identify and fix.

The symptoms of excess moisture and dampness

  • Musty smells in rooms that are closed for any period of time
  • Damp or mouldy clothes or shoes in wardrobes
  • Mould or mildew forming behind paintings, mirrors etc.
  • Stains or watermarks on ceilings or walls
  • Mouldy ceilings and walls, particularly in kitchens or bathrooms
  • Problems with areas of rotting wood in the structure of your house
  • Damp or mould under the house.

Condensation on windows, especially in bedrooms, isn't necessarily a sign of dampness if it only happens occasionally during winter. The easiest solution to avoid lots of moisture forming on windows is to install double glazing.

Sources of moisture

The average NZ family produces around 8 litres of moisture in the home each day from everyday activities such as cooking, showers and breathing. That's normal and can be managed by having the right balance of insulation, heating and ventilation.

However, dampness can also be caused by moisture getting into your house from outside, underneath or from leaking plumbing. Such moisture sources are often hidden and can go undetected for a long time. This can damage your house and reduce its value.

Unless you've actually looked for the source of the dampness, trying to solve it with dehumidifiers and ventilation systems may just mask the problem rather than actually fix it.

Tackling the source

Tackle home dampness problems at their source, and ensure you have adequate home insulation and heat and ventilate your home properly.

If you are having issues with excessive moisture/dampness and poor indoor air quality, follow these steps:

  • Sort your bathroom, kitchen and laundry ventilation.
  • Put a lid on your shower cubicle. They stop steam escaping into your bathroom and are available to fit most new and existing showers.
  • Check under your house. If you can get under your floor check for signs of dampness there. Look for any mould or mildew, Take some dirt and rub it firmly on your hand - if it stains like mud there is probably too much moisture present.
    There are several things you can do to fix underfloor damp:
    - Check for water getting under the floor from drainage, guttering, downpipes or plumbing problems.
    -  Uncover any vents that may have become blocked by plants, soil or to keep pests out. Clear the subfloor area of any obstructions.
    - Get vents installed if there aren't any.
    - Put a vapour barrier down (i.e. thick polythene sheeting) on the ground. This keeps the moisture in the ground and stops the air under the floor from getting damp.
    If you are not sure about any of these actions, talk to a qualified builder.
  • Look for leaks in wall and roof claddings and flashings. Also check for leaks in plumbing services, including moisture getting into walls or floors near showers and baths. Such leaks are often hidden and can go unnoticed for a long time. Non-invasive moisture content measurements are often the easiest way of finding hidden leaks - talk to a suitably qualified and experienced building surveyor who carries out such measurements.
  • Construction moisture. If your house has been recently built or renovated then chances are that there is quite a bit of moisture in some of the construction materials which need to dry out. This may take a few months. Extra heating and ventilation will assist with this.
  • Avoid drying your clothes inside. It is better to dry them outside in the sun and wind, or when the weather doesn't allow this, use an externally vented clothes dryer.
  • Use lids on pots when cooking to reduce moisture release and to conserve energy.
  • Avoid using unflued gas heaters as they release large amounts of moisture and toxic combustion gases into your house. They can also be a fire hazard. If you are using a gas heater or LPG portable heater without a vent or flue to the outside, always keep at least one window open to allow fresh air to enter the room. Never use unflued gas heaters in bedrooms.
  • Use a humidity gauge (hygrometer) to keep an eye on the humidity in your house. This way you'll know when the air in your home is getting too damp (more than 70% relative humidity).
  • Keep furniture away from external walls. Leave a gap of 10cm or more behind large objects like furniture to avoid mould growing behind them in winter. Similarly, keep mattresses off cold floors; put them on a bed base which enables air to circulate underneath.
  • Leave wardrobes slightly open for ventilation.
  • Look for mould regularly and remove it if you find any. Regularly check for signs of mould in your home, including hidden areas like wardrobes, under carpets and behind curtains and furniture. If you find any mould, remove it. Learn more about mould in homes and how to remove it from this PDF on the Department of Building and Housing website.

Good insulation, heating and ventilation

Good insulation, heating and ventilation are also key to managing the amounts of moisture we produce in our homes from everyday activities. For more details on these, have a look at the related pages listed below.

If you have done all these things you shouldn't have any problems with excess moisture and dampness, but if you do, then you may want to consider either a dehumidifier or home ventilation system.


Related pages: