All buildings are potentially at risk of weather-tightness failure, regardless of the building's age, structure or cladding type.  A typical NZ 'leaky building' is generally understood as one where water has penetrated a timber-framed building's cladding system, leading to elevated moisture levels in the building's timber framing, promoting the growth of mould and fungus, which can lead to decay of the timber framing and the growth of toxigenic mould. 

Many factors influence a building's weather-tightness risk, including:

  • The type of cladding system used. The cladding types that are most often associated with weather-tightness defects and damage are texture-coated fibre-cement sheets, cement stucco and EIFS (external insulating and finishing systems).
  • Whether the cladding is directly fixed to the timber framing or whether it is installed over a cavity.  Cladding which is directly fixed to the timber framing offers limited mechanisms for any water that enters past the cladding to drain back outside the cladding, or to dry out, whereas cladding which is installed over a cavity has the chance to drop down the the base of the cavity where it is open to allow drainage
  • Buildings with more than one storey are more at risk of water ingress.
  • Homes with generous overhanging eaves have lower risk of water ingress.
  • Age of the building. Homes built between 1987 and 2005, particularly those built between 1998 and 2005, have a high risk of water ingress.  This is due to the limited knowledge of the effectiveness and durability of cladding products, materials, systems and designs in use at the time, and a generally low level of knowledge and expertise of many of the parties involved in the design, consenting and construction process during that time period.
  • Construction attributes such as membrane decks over living accommodation, decks and pergolas attached to buildings through the external cladding, flat roofs, curved roofs and walls, hidden/valley gutters, parapet walls, complex/angled joinery, skylights, junctions between different cladding types, below-ground membranes and drainage, lack of clearance below cladding at ground level, and roof/wall junctions.



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