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Finding The Root Of Leaky Homes Issue

New Zealand has been plagued by leaky home problems since the mid-1990s, but there may be a permanent solution, writes Anthony Corin.

By: Anthony Corin

31 January 2023

Poor weather tightness in residential construction continues to draw attention to the problem of leaky homes throughout New Zealand.

Leaky homes started to gain attention in the mid-1990s. We blame bad design, insufficient training, cladding selection and inadequate project documentation for this problem’s persistence.

All of these elements contribute to poor weather tightness in a building, but what about the root of the issue? Build materials and systems are critical and may hold the key to fixing leaky homes.


A building’s ability to keep water from penetrating through the external envelope is known as weather tightness. The wet and windy weather in NZ necessitates the use of appropriate building materials and techniques to prevent water damage. In order to design and build suitable solutions within context, site circumstances must be thoroughly examined.

When new materials enter the market industry professionals are compelled to remain commercially competitive by following untested international design trends that are not suitable for New Zealand’s weather. This lack of professional accountability contributes to the persistence of leaky homes which not only negatively impacts the construction industry, but also damages residents’ health, safety and financial well being.


As a response to the rise in leaky homes from the mid-1990s, new rules were included within the Building Act 2004. In accordance with this act, treated timber was reintroduced to prevent rot in timber framing.

Additional regulations would follow such as the Licensed Building Practitioners (LBP) Scheme in 2007, to formally acknowledge builders’ expertise and counteract a DIY, self-taught building culture. This would eliminate lack of skill on the job and restrict unlicensed builders from performing and signing off specific types of work.

Despite these initiatives to address the NZ leaky homes crisis, weather tightness in structures continues to be a significant problem. This can be due to subpar materials, a lack of education, risky designs and insufficient quality control.


When discussing weather tightness, cladding, joinery and wall junctions garner a lot of attention, but how effective are construction systems? Treated wood was reintroduced to reduce the rot and degradation that occurs when wood-framed buildings are exposed to water.

However, while the chemicals in treated wood stop decay, they don’t stop moisture penetrating the wood. The wood swells and warps as a result of this.

As steel does not absorb water, it will not swell or develop mould, making it a solution to leaky homes. However, when exposed to water over an extended period of time, even galvanised framing rusts.

Another building material used here is concrete. Despite its amazing durability, this too is susceptible to water damage. Concrete is porous and absorbs moisture, which causes cracking and structural damage.


All construction solutions mentioned appear to be ineffective at preventing water damage. One technique, though, outperforms the others. Swimming pool formula, poured in place, steel reinforced, waterproof concrete performs exceptionally well in terms of weather tightness. The concrete is made waterproof using a KIM mineral additive that has received Building Research Association of New Zealand (BRANZ) approval.

This is the same material used for swimming pools in order to hold water without needing a waterproof coating. Water is not able to penetrate through the concrete and therefore there is no absorption, swelling or cracking. Additionally, it is composed of inert materials, which prevent decay and degradation.

The solution to New Zealand’s leaky homes may lie in this waterproof concrete, which addresses the issue from the inside out.

Many advocate for a reform of the LBP Scheme to raise industry standards and uphold accountability.

Making information easily available to industry professionals so they can upskill without paying subscription fees has also been suggested.

The construction materials and systems, and what we can do to waterproof them, are a significant factor that needs further thought.

The challenge of leaky homes is still plagued by a variety of problems. It is a complex problem that requires quick attention to ensure the continued supply of high-quality New Zealand homes.


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