Leaky Homes – Why do they leak?

During the 1990s a considerable number of houses were built using methods that haven’t withstood the weather conditions in New Zealand. Because of the problems involving design, and installation of materials, these houses leak when it rains. In some cases the materials themselves were used inappropriately.

Rotting balcony

Once water or moisture gets behind certain cladding types, if there is no cavity between the cladding and the framework, the water becomes trapped and cannot easily escape or evaporate.

Main factors in leaky buildings

No one factor was identified as the single cause of leaky buildings, but a number of causes were identified:

1. Modern cladding systems. ‘Mediterranean’ style buildings using monolithic cladding systems, such as textured wall surfaces made out of plaster on polystyrene or fibre cement sheet, are promoted as providing a sealed and waterproof outer skin and being low maintenance. But often, they have been used outside their specifications or have been installed incorrectly.
2. Inadequate construction that did not allow for deflection, drying and drainage or had insufficient durability and included features such as:
   - recessed windows.
   - flat roofs with narrow or no eaves.
   - two or more stories.
   - design features such as solid balustrades, complex roof design   and envelope shapes where roofs frequently intersect with walls on upper floors.
   - balconies that jut out from the walls.
   - penetrations through the claddings.
3. Insufficient details in the Approved Documents (these contain Acceptable Solutions), which are produced to help people meet the requirements of the New Zealand Building Code. A number of inadequacies were identified, particularly in Acceptable Solution B2/AS1 (about timber durability) and E2/AS1 External Moisture (keeping the weather out). These have since been amended. Problems with the administration of the Building Code by councils and building certifiers have also been identified.
4. Lack of technical knowledge and skills when houses are designed, detailed and built – modern systems require a greater level of care and skill which has not always been applied.
5. Untreated kiln-dried framing timber is susceptible to rot when moisture penetrates the building envelope.

This excerpt is published from the consumer build website. More detailed information on the subject can be found there.