Current Leaking Building Issue: The Leaking is Not New – the Extent of the Failure is.

December 14, 2013

By Greg O’Sullivan



In 1995, Prendos pointed out to the construction industry that there were problems with the application of solid plaster stucco to our buildings. In particular, the application of plaster directly onto a single building wrap fixed against the framing. This produced a dramatic industry response because of news articles published in the Herald recording these concerns. In particular, BRANZ responded by providing education seminars and more particularly, producing the Good Stucco Practice Guide, one of many practice guides that they have since produced.During the same period I was dealing with failures with stopping compounds and flashing techniques with textured fibre cement and external insulation finishing systems, often referred generically as ‘monolithic’. The problems occurred where the cladding met external joinery or because of complex design. Often there was a high reliance on sealants that did not bond properly to the substrate materials. These specific problems were above and beyond poor trade practice or lack of knowledge. There was a need for further weathertightness science in the industry. Given this background of known cladding failure it was surprising that the New Zealand Standards released a new Standard NZS 3602 in September 1995 indicating that untreated pine could be used to frame building. The use of untreated timber happened in mid to late 1997 by which time, the Building Industry Authority had approved that Standard as an acceptable solution to the Building Code.

Discovery of the New Concern

What did this mean? It meant most of the timber used in buildings for framing was now untreated radiata pine. At the coal face, we started finding decay occurring earlier and more vigorously than we had previously experienced. In checking with Forest Research, they confirmed that the treatment chemical boron, even though it was there primarily as an insecticide, was a very effective fungicide, particularly against brown rots. And so started the episode where this company canvassed and urged the industry to wake up and realise that it was facing a very serious issue, the possibility of a lot of seriously decayed recently built buildings. The forestry companies at the time stated with logical simplicity: “timber won’t rot if water doesn’t get in.” This simplistic view is incorrect because it assumes that all buildings shall be built in a perfect fully watertight manner. This would be a bit like building a submarine or perhaps an aircraft. In simple terms this is nonsense. In my early life, 30 years ago I worked for a family design/build company who prided itself on its ability to design and build buildings that performed. They went to great lengths to use flashing design to keep leaks out of buildings. However, even with this high degree of care in the design and construction process, occasionally they would have to deal with some leaks and deal with them they would.

Good Builders Can Now Fail

That was not peculiar just to my father’s and uncle’s family business, today there are builders who I acknowledge to be good in the fact that if, for some reason, they fail to build absolutely correctly and there is a resultant leak, they do not walk away, they go back and attend to the problem, this is normal practice. However, the decay with untreated timber is serious and very rapid. A timber frame can be completely lost before they know a leak has occurred. Minor leaks now can cause major frame destruction. Damage now lurk behind a lot of the claddings and occupiers will not know for a long time. The destructive nature of this decay is only revealed when claddings are removed or the leak is so severe it can be seen internally. Seeing is believing!! If you have not experienced the removal of outer claddings and seen for yourself the utterly decayed timber behind, it is impossible to fully understand or comprehend this difficult problem. It is probably impossible for the average person to completely understand the seriousness of the issue. The sad thing is it does affect the average person. Part of the fabric of their being is attacked ? their basic need for shelter.

At Last the Industry is Waking Up

It is now with some relief that we see that the Overview Committee set up by the Building Industry Authority has come out and acknowledged that a problem actually exists. They acknowledge that a return to some basic principles of construction need to be achieved. This is a noble statement. However, I do not agree with it. It is not enough. It is too simplistic to think all can be fixed by going to weatherboard or brick construction. Modern materials used now do have a lot going for them. It is the specifics of how they are designed into building systems that has been their downfall, coupled with the rapid decay of untreated timber in only damp conditions. These new cladding materials can and will successfully continue to be used. However, there must be, behind every cladding element, a second line of defence such as a drained ventilated cavity. Where possible eaves should always be part of the design. Ply for instance as a drainage plane is insufficient. The use of a membrane would be disastrous.

The Four D’s Principle is an Answer (Deflect, Drain and Dry, Durability)

What does this mean?It means the building should be able to first deflect water with eaves and then accept some minor water in and drain or dry it out, that is exactly what brick veneers do if built correctly. Using drainage with good flashing and air seal design and drying air in to diffuse and dissipate water will remove minor water leakage after it stops raining. It sets up a generally dry environment. If, for some reason, a very minor leak occurs that bridges this defence then the framing requires a moderate level of boron treatment so the builder has an opportunity to attend the site and repair the problem at little cost and inconvenience to the occupier. This makes up the 4 D’s of good weather design. Deflect (with eaves), Drain and Dry (cavity systems) and have sufficient background Durability (boron treatment in the framing).

Weatherproofing of buildings is not a simple but a difficult, sometimes very complex procedure. The exposure, wind patterns and differing site circumstances all can lead to a completely different set of required solutions for each individual building. The more complex the architecture, the more difficult the problems of weathertightness design became.

The discovery of the extent of the present decay problem is only in its infancy. Unfortunately there also are people who are now repairing buildings badly. They are covering up decayed timber. They are putting untreated timber back into areas where decay fragments remain and leaked water is still held by the building. They use paint systems over wet areas that hold moisture. They lift membranes from decks and put new membranes down entrapping moisture that has accumulated. All of these things add to the problem we now face and will face for some time into the future.


This Issue Must be Solved

It is critical for our industry, including all property sectors, that these problems are overcome. Our largest cities, Auckland in particular, needs intensive terraced housing and multi apartment dwellings to accommodate a growing population to contain the urban spread. Therefore, weathertight solutions to building are needed right now. Unfortunately, building science has lagged far behind and it will take years for it to fully catch up. It should be a priority for the government and the building industry and something that the public should demand of right. We need to learn “quickly” how to develop building systems that will work after they are site constructed. We need to be able to accurately survey existing buildings for problems. First and foremost, however, we should immediately return to a level of treatment in timber that gives some protection and thus reduce repair costs. We do not need to go to high protection treatment. We need a basic protection level so that eventually the builder can buy the frame, erect it and later return if there are minor leaks without facing massive decay and repair bills that will probably drive them into liquidation.

In Summary

It is important to realise that we must get our weathertightness design correct. H3 treatment in timber will not stop the development of unhealthy moulds in our wall cavity framing areas. These have been related to sickness experienced by building owners and builders doing repairs. Therefore any solution must be one which aims to create a dry environment, not by making buildings perfectly watertight (utopia) but to design them to handle the water in a manner that keeps them dry. The hope is that the present problems, terrible as they are, will lead us, as an industry, to be able to build more effectively and with greater success. We must learn to manage these issues that we now face and get over the huge repair bill that will have resulted from these problems and the use of untreated timber.Statistical analysis of typical failures in graphic form with commentary from Philip O’Sullivan (Dr Rot) is in ‘Pilot Study on Leaking Buildings‘.


Greg O’Sullivan is the founding director of Prendos Limited and an expert in the area of building failure and in particular, weathertight issues and has, in the past, highlighted to the industry many of the material failures occurring with products used to clad buildings. He is a BRANZ Accredited Adviser, Registered Building Surveyor, Immediate Past President of the Institute of Building Surveyors, Fellow of the Arbitrators’ and Mediators’ Institute of New Zealand and sits on both Mediation and Arbitration Panels and is on the Advanced Panel for Mediation with LEADR.

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