Tackling dampness

Condensation, moisture and mould are all too common in NZ homes. About 30% of our homes suffer from problems associated with moisture internally. In a large number of these houses, 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

Most Kiwis are familiar with the symptoms of excess moisture and dampness in their homes, which include the following:

• 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 wallse
• 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.

It is worth noting that condensation on windows, especially in bedrooms, isn't necessarily a sign of dampness or excess moisture if it only happens occasionally during winter. The easiest solution to avoid moisture forming on windows is to install double glazing.

Sources of moisture

The average NZ household 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, high moisture levels can also be caused by dampness getting into the home from outside, underneath or from leaking plumbing services. Such moisture sources are often hidden and can go undetected for a long time. Apart from making your home unhealthy to live in they can rapidly erode the structural integrity and value of the house.

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 thinking about getting a home ventilation system or dehumidifier, make sure you do these things first.

If you are having issues with excessive moisture/dampness and poor indoor air quality, EECA recommends the following steps:

Sort your bathroom, kitchen and laundry ventilation. Ensure that there is effective ventilation from wet areas in the home (such as the bathroom, laundry and kitchen) to minimize the moisture that causes the problems. Install an externally vented range hood or extractor fan over your cooker, an externally vented extract fan in your shower/bathroom and exhaust laundry dryers to the outside.

Extractor fans need to be sized and located properly for the size and type of room - ask your supplier for advice on this. Leaving the bathroom window open allows air flow into the bathroom and will improve the extract fan's effectiveness. After a shower, let the fan run for a few more minutes. Clean your extractor fans regularly to maintain their performance.

Check under your house. If you have an enclosed basement, check for signs of dampness there. Look for any mould or mildew growing on the ground or on materials. Take some dirt and rub it firmly on your hand - if it stains like mud there is probably too much moisture present. To remove moisture rising from the ground, enclosed basements must be ventilated through gaps or vents around the perimeter walls. Uncover any vents that may have become blocked by plants, soil or to keep pests out. Clear the subfloor of any obstructions like stored timber or rubbish. Also fix any drainage, guttering, downpipe or plumbing problems, i.e. water flowing under your house after rain or from leaking pipes. If the sub-floor is still damp, look into installing additional vents and/or fitting a vapour barrier to the ground underneath your floor (i.e. polythene sheeting).

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 built or renovated only recently chances are that there is quite a bit of moisture in some of the construction materials which needs 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.

Keep furniture away from external walls. If you place large objects like furniture too close to poorly insulated external walls you're almost guaranteed to get mould growing behind it in winter. To avoid this, leave a gap of 10cm or more to allow room air to circulate behind it. 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 key to managing the amounts of moisture we produce in our homes from everyday activities.

Insulation is important because poorly insulated walls, ceilings and floors are cold and attract condensation. Condensation promotes mould and mildew which is bad for your health. Furthermore, poorly insulated homes are hard and expensive to heat. Learn more about Insulation.

Heat your home properly. A cold home is likely to be a damp home. Heating is important because warm air can absorb more moisture which can then be removed from the home through ventilation. It's better for your health too. Aim for a minimum of 18°C in the rooms you're using (or 20°C if you've got vulnerable people like young kids, the elderly or the ill), and 16°C in bedrooms overnight. Learn more about Heating your home.

Ventilate your home regularly with fresh outdoor air to expel stale, humid indoor air. The simplest way to do this is to open windows and doors at least once a day for a few minutes, and leave a window slightly open in your bedroom overnight. Learn more about Ventilation.

Consider double-glazing your house. Single-glazed windows are areas of high heat loss and will always attract condensation in winter. Learn more about Double Glazing.)

Once you have looked at all these things you really 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.