Weathertightness

Weathertightness refers to how effectively a building keeps moisture out. In New Zealand, this issue became a national crisis in the early 2000s when thousands of homes built between the mid-1990s and mid-2000s were found to have serious moisture ingress problems — commonly known as the 'leaky building crisis'.

The crisis was caused by a combination of factors: monolithic cladding systems (plaster-style exteriors with no drainage cavity), inadequate flashings, flat or low-pitch roof designs, untreated timber framing, and poor quality construction. When water penetrated the cladding and couldn't drain away, the timber framing rotted, often invisibly behind the walls.

The New Zealand Building Code clause E2 (External Moisture) sets the performance requirements for weathertightness. Changes made after the leaky building crisis include mandatory use of treated timber, requirements for drained and ventilated cavities behind claddings, and improved flashing details.

Weathertightness failures can cost $100,000-$500,000+ to repair and can make a property structurally unsound. Any property built between 1995 and 2005 with monolithic cladding, Mediterranean-style design features, or flat roofs should be considered higher risk.

Get a thorough pre-purchase building inspection with specific attention to weathertightness. For higher-risk properties, consider an invasive moisture test where the inspector takes moisture readings from within the wall cavity. Check the LIM report for any weathertightness-related building consents or WHRS claims.

A qualified building inspector should assess weathertightness as part of a pre-purchase inspection. Non-invasive moisture meters can detect moisture behind cladding. For higher-risk properties, invasive moisture testing (drilling small holes to test inside the wall) provides more definitive results. Check the LIM report for any Weathertight Homes Resolution Service (WHRS) claims or remediation consents.