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Causes and effects of high moisture

High moisture levels make your home uncomfortable and unhealthy, and can damage its decor, furniture and even structure.

Managing moisture in your home

Just under half (44 per cent) of owner-occupied houses and 56 per cent of rental houses had visible mould according to a 2015 BRANZ Housing Condition Survey [PDF 750 KB].

High moisture levels and mould are associated with health problems including asthma, eczema and headaches.

With good design, maintenance, ventilation (including venting cooking vapours, bathroom steam and clothes dryers outside) and insulation, you can keep your home drier and healthier.

Why does moisture matter?

High moisture levels:

  • can damage paintwork, wallpaper, wall linings and curtains
  • encourage the growth of moulds, fungi, dust mites and mildew, which can be harmful to your family’s health
  • make your home harder to heat, and make your power bills higher
  • can cause timber decay and other deterioration in your home and contents
  • make your home less comfortable to live in.

Up to 15 percent of New Zealanders are allergic to moulds, spores and their by-products (which are sometimes toxic) that grow in most households. The allergies commonly appear as asthma, headaches, eczema, gastroenteritis and sneezing fits. Damp homes are associated with increased numbers of doctor visits for respiratory problems such as asthma, and lost work and school days.

Causes of high moisture levels

High moisture levels can be caused by:

  • moisture getting into the home from outside – especially from leaks and damp ground beneath the house
  • water released from household activities such as showering, washing, cooking and even breathing
  • moisture released from unflued gas heaters
  • inadequate ventilation.

Moisture created by common household activities

ActivityLitres
Cooking 3 per day
Showers and baths 1.5 per day, per person
Dishes 1 per day
Clothes drying (unvented) 5 per load
Gas heater (unflued) Up to 1 per hour
Breathing (active) 0.2 per hour, per person
Breathing (asleep) 0.02 per hour, per person
Perspiration 0.03 per hour, per person
Pot plants As much as you give them

Moisture in new buildings

In new buildings, some moisture is trapped during the construction process and can take time to dry out. Trapped water is mainly from new building materials, specifically timber and concrete. The house will dry out eventually over the first year of the building's life, as long as the house is properly heated, ventilated and insulated.

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Other resources

  • BRANZ 2015 House Condition Survey

    Download a free copy of the 2015 House Condition Survey report from the BRANZ website.

  • BRANZ online shop

    You can buy bulletins on passive ventilation, ventilation of enclosed subfloor spaces and preventing construction moisture problems in new buildings from the BRANZ website.

  • EECA guidance on dampness

    You can read about ways to deal with dampness on EECA’s Energywise website.

  • Asthma Foundation

    This website has tips for a healthy home, and fact sheets to help you look after your health.

Note that this document is published by the Ministry of Business, Innovation and Employment Chief Executive as Guidance under Section 175 of the Building Act 2004. This is a guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case.