Leaky Building Syndrome?

The New Zealand Building Act 1991 reduced statutory controls and national standards for the construction industry.

A new philosophy was introduced: market forces would determine the required building standards.

This proved to be an expensive experiment over the following 13 years. It turned out that the market couldn’t be trusted, and there is a role for government regulatory agencies after all.

This relaxation of the regulations coincided with an increase in the use of polystyrene as external insulation on houses. Expanded polystyrene sheet was fixed directly to standard timber framing. The main waterproofing in the system is provided with a thin acrylic paint coating over the polystyrene.

(Another poor building system was texture coated fibre cement sheet.)

The problem is that structural timber moves, shrinks, expands. The building as a whole can move through wind or earthquake forces. Cracks can develop in the waterproof layer, and water penetration can cause deterioration of the structural timber in the exterior walls. Poor construction techniques meant that buildings of this type could also leak around the windows.

Due to insulation and poor ventilation water can be trapped within the wall. The high moisture levels in the timber encourages insect or fungal attack.

There is another issue. In the early 1990s there was some concern about the toxic nature of the chemicals used to treat pine timber. For some reason in 1998 it was decided to allow untreated pine in buildings, even for structural members.

If untreated timber is continuously damp it can deteriorate and quickly lose its structural integrity.

This combination of factors meant that buildings leaked, and many ended up with serious structural problems.

This is known as “Leaky Building Syndrome”.

The costs of rectification have been in some cases more than the original cost of building the home.

It took until the much more stringent Building Act 2004 before all building timber was required to have preservative treatment, and the construction of polystyrene clad buildings was required to have a ventilated, drained cavity, separate from an internal waterproofing layer.

With these changes to the construction requirements if the exterior of the building allows water through the outer layer there is an inner layer to stop moisture getting anywhere near the structural timber. And structural timber can survive getting damp due to preservation chemicals the timber absorbs.

A report issued in July 2009 by Pricewaterhouse Coopers estimated there were anywhere between 42,000 to 89,000 homes throughout New Zealand affected by leaky building syndrome, constructed between 1992 and 2004 using inadequate building techniques or materials.

It is estimated that the leaky buildings will eventually cost the New Zealand economy about $11 billion. The Weathertight Homes Resolution Services Act 2006 allowed the government and local government to contribute 25% of the cost of repairs, but claims needed to be made within 10 years of construction. No further claims are allowed due to the expiry of this time period.

But the deterioration of the affected timber can take many years to become apparent.

Some of the early repairs were targeted to small areas or were otherwise inadequate. Some houses have not been fully rectified and leaking may cause further problems in the future. Full recladding with an approved new system may not have been done.

There are many homes in the Nelson region which had been built during this time period with a sub-standard construction method.

Bear in mind, however, that following the 2004 changes to building requirements, houses with ventilated cavities are a totally acceptable way to build.

The best you can say about potentially leaky buildings is that they haven’t leaked yet.

And if potentially leaky buildings do leak and structural damage occurs all costs of repairs are now totally the responsibility of the current owner.

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