Condensation & mildew – the winter problem

- Aneco Sustainability Solutions

What Causes Condensation?

All air contains water vapour, but it can only hold a limited amount without becoming saturated. The higher the temperature, the more it can hold. If there is too much moisture in the air for the temperature, some will condense on the cold surfaces of the house – windows and uninsulated walls.

Condensation is widespread but is worse in colder climates. It occurs on windows, especially metal framed ones, walls and ceiling linings. It can leave water stains, help rot to set in and cause mildew growth.
If you have a problem with condensation, the first thing you need to do is consider where the water is coming from.

Sources of Moisture

Activity	Litres
Cooking	3 per day
Clothes washing	0.5 per day
Showers and baths	1.5 per day per person
Dishes	1  per day
Clothes drying	5 per load (unvented)
Gas heater	up to 1 per hour (unflued)
Breathing, Active	0.2 per hour per person
Breathing, Asleep	0.02 per hour per person
Perspiration	0.03 per hour
Pot plants	as much as you give them

      

Keeping the Humidity Down

1. Ventilation takes away the moisture released from cooking, showers, clothes dryers and breathing.
2. Heating raises the temperature and allows the air to hold more moisture.

NB. Ventilation is the most fundamental need. Until there is enough ventilation, nothing else can help, although too much may increase the problem by preventing the house or premises from warming up. Both insulation and heating throughout the home will assist, but not prevent, mildew and condensation.

How and When to Ventilate

• Ventilate little and often. Many windows open slightly are better than one fully open. If windows start steaming up, open them wider.
• Keep rooms ventilated and warm during winter - at least 5°C warmer than outside temperatures. Install heavy curtains and draw them at night: it helps keep the home warm and reduces the number of cool surfaces for water vapour to condense on. Leave windows closed on damp days.
• Short bursts of vigorous ventilation are of little value except when flushing out moist air. This should be done after a bath or shower.
• Close doors when cooking, showering, using the dryer, to limit spread of moist air to other areas of the house.
• Always use close fitting lids on pots when cooking and fit extractor fans over the cooktop or stove and try to expel steam/moisture and odours from cooking areas and showers directly to the outside. These must be ducted right to the outside air and not just into the ceiling space.
• Vent clothes dryers to the outside and don’t hang clothes inside to dry.
• Use a cupboard heater in problem wardrobes. A ventilation grille in the top of the wardrobe will also help.
• Limit the number and size of pot plants in the house.
• Check the ground under your house is dry. If it’s wet, cover with polythene (if feasible), taping the joints, and ensuring a tight fit around piles. Check that drainage systems are diverting water away.
• Fix any leaks in the roof or around windows.
• There are ventilation systems that provide continual ventilation of the house taking dry air from the roof space and pushing it into the house, forcing the damp air out the of the house. Some models can also act as a heater, by warming the incoming air.

What Causes Mildew?

Mildew is a primitive form of plant growth. It grows from spores that abound everywhere and will grow in any home or premises where the humidity remains high. Mildew can occur in any type of construction and is common in both mild and severe climates. It’s often found on shoes and clothing in wardrobes, on wallpaper, curtains and ceilings.

How to Prevent Mildew

• Make sure there is some ventilation in all rooms at all times..
• Keep the house warm, not too hot. Try to keep the indoor temperature at least 5°C warmer than the outside temperature at all times.
• A little heating kept on continuously does more good than a lot of heating during the evening only.
• Avoid pots or pans boiling longer or harder than necessary.
• Refrain from drying clothes indoors. Make sure that clothes-dryers are ventilated to the outside.
• Prevent steam from showers spreading through the house by keeping bathroom doors closed, windows slightly open, and installing extraction fans.
• Avoid the use of LPG, kerosene and unflued gas heaters without proper ventilation.
• Provide permanent ventilation to wardrobes by leaving the doors ajar or provide ventilation at the top and bottom of the door. Dehumidifiers or permanent ventilation systems may be effective.
• Insulate the ceilings, walls and floors of new dwellings (a legal building requirement) and where possible the ceiling and walls of existing homes. Any alterations or additions need to be fully insulated.
• Use windows as a guide. If they start collecting too much condensation, open them a little wider.

How to Deal with a Mildew Attack

• If mildew grows on wallpaper or ceilings, clean it down with a damp cloth and household bleach solution (one part bleach and five parts water), being sure to wear rubber gloves and eye protection. Just washing the mildew with soap and water will only spread the fungus. Try a small area to make sure that the bleach does not take the colour out of the wallpaper. After drying, wipe off the solution with a clean damp cloth.
• If the colour is affected, try a fungicide solution available from hardware shops.
• If stains cannot be removed by either method, it may be necessary to repair the wall which will involve removing the wallpaper. Paint the wall beneath with a fungicide solution, then when properly dry, re-wallpaper using a synthetic paste (not flour) containing a fungicide.
• Gloss painted surfaces can be wiped down with a household bleach solution while matt paints can be wiped with a fungicide solution to avoid removing the colour.
• Water based paints can support mildew so after any treatment use an oil-based sealer first. Never paint directly over untreated mildew.
• Slight mildew on curtains and clothing can usually be washed out, but if left may cause permanent staining.
• When repairs are completed, make sure you avoid any recurrence of mildew by keeping your house moderately ventilated and warm, and avoid creating too much moisture.

Contact Aneco Sustainability Solutions 04 499 3599 email info@aneco.co.nz