Condensation and mould Why do some tenants have it and some dont in the same house

Posted on Thursday, June 11 2015

While landlords are spending more and more time and money insulating and providing heatpumps and other forms of heating, tenants seem to complain more about condensation and mould. There are usually tell tale signs when you take a look at how they live.

Condensation can only escape when in vapour form. To be in vapour form, the air must be warm. Therefore the best time to open windows is when the house has been heated. Once the house cools down, the moisture condensates and is now in liquid form. Opening the window will be of little help as the water will continue to sit there until the house is heated again.
Therefore the perfect solution is to either have windows slightly open all of the time so when the house is warm, the moisture can escape. Or heat the house up in the morning say, then throw open the windows before leaving for work or leave them open an inch on security stays for the day. Close them and heat the house up again. Even open the windows in the living rooms while getting ready for bed (having had the living areas warm all evening)
When you look at how tenants live who suffer from condensation, some will keep their bedroom doors shut and not open their windows. They often dry their clothes inside during winter, again with the windows shut. Tenants may think they are saving money by not heating the house, just the one room they are all in together in the evening but they are not saving money as moisture is not escaping and day in and day out, the moisture will build up – damp homes are more expensive to heat. Others will throw open the windows for hours on end which you would think would do the trick. However they open the window from a cold start when the water is already in liquid form and can’t escape. The windows are then closed and the house heated again. Dry houses heat quicker and are much cheaper to heat than houses full of moisture which can’t escape, created by tenants.
There is copious amounts of information on the internet on the subject and we keep copies of a number of these in the “kit” to hand out at inspection time when we see the tenants are not looking after the property properly in respect of condensation which leads to mildew and mould.

Water rots timber such as wooden window frames. The water sits on the lower frame and over time tracks down behind the glass, rotting out the timber from the inside.
Moisture will reduce the life of plaster & plasterboard, carpet, timber, curtains, paintwork, etc etc.
Houses with excess moisture levels are much more expensive to heat than dry homes
Mould will form on walls, behind curtains, inside wardrobes and around the edges of carpet. Mould can trigger health problems for the tenants and deteriorate soft furnishings more quickly. Mould is difficult to remove entirely once there are spores within the house.
Where possible extract large quantities of moisture with the use of a good quality extractor fan in the bathroom, range hood in the kitchen and external venting for clothes dryers. Provide tenants with an area they can hang clothes undercover outside to minimise the use of clothes airers inside. Fit window security stays on windows to enable tenants to leave windows open when not at home.
Tenants have the main responsibility to ensure that the property is ventilated and heated adequately to ensure moisture does not build up.
They need to open plenty of windows (ideally a small amount for long periods of time) and leave doors open to enable air flow around the home.
Heat the property to at least 5° above the external temperature of the house to enable the moisture to be carried out of the property through the open windows (The World Health Organisation recommends a minimum internal temperature of 18°C)
Leave windows open in the bathroom but leave the door closed after showers to prevent the moisture from being drawn into the rest of the house.
Do not use unflued gas heaters as they produce a lot of water vapour.
Although dehumidifiers help they are no substitute for adequately heating and ventilating homes.

FURTHER INFORMATION: design/moisture/ has a useful table of the moisture created by common household activities including 3 litres produce by cooking each day, and 1.5 litres produce per person per shower and 5 litres per load of clothes drying unvented! has a table of running costs of appliances which is useful as any discussion on condensation, ventilation and heating will result in the cost of heating etc. provides a lot of detail on the subject including the use of mechanical ventilation systems.

The University Accommodation office produces an excellent one page flyer for flat dwellers on condensation which has a superb conclusion

Usually not. Buildings don’t make excess steam
Buildings don’t shut their windows
Buildings don’t turn off all heating
Buildings don’t hang wet clothes about

That sums it up nicely…

Tania and Kyle Elmer
Mana Property Management Ltd

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Expert's Bio

Tania & Kyle Elmer

Tania & Kyle Elmer are active investors with a large portfolio of properties in Dunedin and Central Otago and mentor investors in the techniques used to grow wealth through property investing. Kyle and Tania are Co-directors of the Leading Property Mangers of New Zealand (LPMNZ). Kyle is a past president of the Otago Property Investors Association (OPIA). They founded Mana Property Management Ltd to provide specialist management services to Discerning Landlords dealing in the quality end of the market. | Find Kyle on Google+

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