Moisture Intrusion in New Zealand Homes

Moisture intrusion can be the cause of building defects, as well as health ailments for the building's occupants.

Some common moisture-related problems include:

  • structural wood decay; 
  • high indoor humidity and resulting condensation;
  • expansive soil, which may crack the foundation through changes in volume, or softened soil, which may lose its ability to support an overlying structure;
  • undermined foundations;
  • metal corrosion;
  • efflorescence and water staining to cladding; and
  • Mould growth.  Mould can only grow in the presence of high levels of moisture. People who suffer from the following conditions can be seriously (even fatally) harmed if exposed to elevated levels of airborne mould spores:
    • asthma;
    • allergies;
    • lung disease; and/or
    • Compromised immune systems.


How does moisture get into the house?

Moisture or water vapour moves into a house in the following ways:

  • Air infiltration. Air movement accounts for more than 98% of all water vapour movement in building cavities. Air naturally moves from high-pressure areas to lower ones by the easiest path possible, such as a hole or crack in the building envelope. Moisture transfer by air currents is very fast (in the range of several hundred cubic feet of air per minute). Replacement air will infiltrate through the building envelope unless unintended air paths are carefully and permanently sealed;
  • By diffusion through building material. Most building materials slow moisture diffusion, to a large degree, although they never stop it completely;
  • Poor construction. Incorrect installation of cladding or lack of flashings can allow moisture to penetrate the framing timbers and move into the dwelling;
  • Insufficient or poorly installed spouting;
  • Leaks from roof;
  • Plumbing leaks; 
  • Flooding, which can be caused by seepage from runoff or rising groundwater; and
  • Human activities, including bathing, cooking, dishwashing and washing clothes. Indoor plants, too, may be a significant source of high levels of humidity.


Common areas of moisture intrusion:


A roof leak may lead to the growth of visible mould in the ceiling space that can grow unnoticed.

  • Lack of maintenance to a roof increases the risk of leaks as the paint or coating degrades over time, and fixings begin to rust. Lead head nails are a very common source of this as they rust from the inside out.
  • Flashings around junctions and penetrations to the roof should be thoroughly checked and are a common area of failure. We often find missing kick-out flashings which allows the moisture to enter into the cladding and framing.

Leaking spouting


  • Distribution pipes and plumbing fixtures can be the source of large amounts of moisture intrusion. If the wall is moist and/or discoloured, then moisture damage is already in progress. Most plumbing is hidden in the walls, so serious problems can begin unnoticed. A non-invasive moisture inspection as part of a pre-purchase home inspection is critical to identify these concealed leaks.
  • One of the most important means of moisture management in the bathroom is the exhaust fan. A non-functioning exhaust fan overloads the bathroom with damp air. Ventilation fans should vent into the exterior and not the ceiling space.
  • Incorrectly installed showers a very common – we often find leaks by the corners or from the shower waste.
  • Mould growth and silicone repairs can be a sign of moisture issues around baths and showers so these areas should be investigated further.
  • Spouting and downpipes are another area of risk; they should be checked for correct installation and fall, adequate overflows, and connections to approved storm water outlets.

Mould around plumbing

Ceiling Space:

  • Look for stains or discolorations at all roof penetrations. Chimneys, plumbing vents and skylight wells are common places where moisture may pass through the roof. Any such locations must be inspected for wetness, a musty smell and/or visible signs of mould.
  • The condition of insulation can also be a good indication of moisture in the ceiling space – signs such as dampness, water staining, discolouration, compression, and mould, are all common signs of moisture ingress.
  • Rust or corrosion around recessed lights are signs of a potential electrical hazard.

moisture in the ceiling space


These days new constructions typically require damp-proofing of foundations where as older homes typically relied on ventilation grilles. Ventilation grilles should be checked to make sure they are clear of debris that can block airflow, and a moisture barrier in the subfloor can be installed to prevent raising damp.

damp subfloor


In summary, moisture can enter a building in a number of different ways. High levels of moisture can cause building defects and health ailments. 

If you’re purchasing a home, or concerned about moisture in your current home, contact our team at NZ House Surveys – we have all the tools and knowledge to carry non-invasive and invasive moisture testing. Phone 0800 487 884

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