Monolithic Clad Houses and Untreated Timber

What is a 'Monolithic clad' house, and why are they often blamed for the leaky home problem?

To explain simply, the 'cladding' of a home is the material used to line the outside walls. This can be weatherboards, brick, blocks, or a plaster-like 'stucco' finish.

According to the buildingguide.co.nz, the definition of 'Monolithic' cladding is:

"A cladding of sheet material forming a continuous mass, with an applied coating to give the appearance of a seamless cladding" 

This style is popular for its clean, modern lines and the flexibility it allows designers. Unfortunately though, deregulation and a lack of skill in the building industry led to tens of thousands of sub-standard homes being built in the mid-to-late 90'.

The main problem was that these predominantly plaster coated monolithic clad homes were letting water in to the wall cavity, but not out again. Whereby a traditional weatherboard home has an airspace behind and below the weatherboards to allow moisture to drain or dry out, the monolithic clad homes had none. Moisture would simply become trapped within the wall. One of many common water entry points was through poorly sealed window aperatures, where there was poor or no flashing to prevent it.

This was bad enough, but from around 1997 the law changed to allow 'untreated' timber to be used in homes. Timber no longer needed to be treated with Boron, which prevented borer. However, the treatment also improved rot resistance. The combination of leaky monolithic clad construction, water trapped within the walls, and the weakened resistance to rot of the timber resulted in the problem we have today. 

In 2002 the government commissioned a report investigating the issue (the 'Hunn' report), which led to an updated version of the Building Act in 2004. This required that an air-cavity be built into monolithic clad houses to aid draining, and required the use of treated timber. Many design parameters were tightened up where the risk of moisture ingress where concerned as well. 

In addition to the 2004 Building Act changes, the government set up a new Tribunal specifically for leaky home claims, the Weathertight Homes Tribunal. Here, claims for compensation, and later damages by leaky home owners could be heard without clogging up the magistrate system.

Unfortunately, the cost of litigation brought about by repair claims was crippling local councils, who were being sued for negligence when inspecting and issuing code compliance certificates for these homes. They asked the government for help.

To discover just how big the leaky home problem was, the government commissioned another independent investigation of the situation by Price Waterhouse Coopers (PWC) in 2009. This report estimated there were approximately 42,000 leaky homes in New Zealand, and the cost to repair them could reach $11.3 billion.

Based on the findings of this report, the government introduced the Financial Assistance Package in 2011, in which the government contributes 25% to approved repairs.