Leaky Buildings — Part 1 — How did we get here.

By Ken Collins 20/05/2010 9


With the government announcing it’s IMG_7549-web(our) package to help solve the leaky homes crisis this week, it has brought the spotlight back onto what is now a highly emotive subject. While the emphasis is rightly on getting peoples homes safe and fit to live in, it should be remembered that the leaky buildings problem is wider spread than just domestic buildings. Recent reports have shown that it includes schools, commercial and community buildings.

The politics of it is complex and controversial with blame-storming rampant. The reality is that there are so many aspects to obtaining a completed building, from design to move in, that you can’t just point your finger a one person or organisation.  Additionally the physical causes, effects and remedies are only now becoming well known and well understood.

So how did we get here?  In effect it was a combination of a number of issues, coming together all at once.

Ever since humans have built structures and shelters on this land, they have leaked, for one reason or another. In the early 20th Century buildings leaked, however the timber that was used was good strong native timber, which could withstand being wet and then drying out again. The gaps and construction technologies of the day meant that there was airflow through and inside the building structure, which allowed it to dry out. These days everything is sealed up like a chilly bin and any water that does get inside the structure can’t get out again. The timber stays wet, fungus grows and timber rots.

The use of un-treated timber was approved when the kiln drying of timber had become commercially available. Up until then all timber was naturally air dried and would normally be stood up as framing while it was still well above 20% moisture. It would then dry out as the house was completed.  The testing of the day showed that ‘dry’ timber (at it’s moisture equilibrium of about 12-15%) didn’t need treating, assuming it stayed dry. It also meant significantly less energy, chemicals and heavy metals were used in the building industry.

However history has proved that some of this timber didn’t stay dry.Imported-Photos-00026-web

What people also didn’t realise was that the old Boric treatment applied to timber being used internally (to stop borer attack) actually provided some protection against fungal attack when it did get wet.

At the same time the design fashion of the day changed to the use of parapets and low pitch roofs, monolithic plaster wall systems, and the mixing of different cladding materials on the one building.

New cladding materials and cladding systems relied to heavily on thin top coats where the base materials are not inherently water proof, or where jointing systems have proven over time to be ineffective or to be difficult to install and maintain.

The use of sealants to provide flashing and waterproofing barriers increased exponentially, at the expense of mechanical flashing systems. People relied on these chemicals to stop water getting into all sorts of little (an not so little) openings. So while sealants work very well when they are installed properly, they do need maintenance and replacement, especially where they are exposed to UV light.  However all to often they weren’t used or applied in ideal conditions and they failed prematurely as a result.

Added to this there was a lack of continuity across all the disciplines in the building industry, where traditional roles and responsibilities were fragmented.

Despite all of this, it must be pointed out that at the time the majority of people involved in the building industry thought they were doing the right things. Products were researched and tested, assessments and decisions made on the information available. Yes there were (and still are) some dodgy developers, builders and designers out there, but in no way can they account for all of the problems we are now observing.

One of the biggest realisations has been that despite the knowledge obtained from testing IMG_5557-webconstruction and cladding systems to assess their suitability for New Zealand conditions, the true test has been their actual performance in the real world over 5, 10, 20, 40 years. It is particularly hard to assess likely in-use performance by doing accelerated weathering experiments and the like. Often people relied on overseas testing and research, which wasn’t always totally applicable to NZ conditions.

The result is that in the last 10 years many methods that were thought to be ok, have proven to not be. Manufacturers have changed their installation, fixing and jointing instructions. A number of products that were tested as being suitable for NZ buildings have been withdrawn after they were found to fail. This includes products that were assessed by the Building Research Association of New Zealand (BRANZ) and given a BRANZ Appraisal Certificate, only for that certificate to be withdrawn later when problems arose.

What was thought to be best practise 10 years ago, now isn’t and so things have changed, and will continue to do so.

The fact is that you can never know with 100% accuracy how a material or a system will perform until it has actually been in use, in the environment, for a period of time. There are so many variables of, exposure, wind loads, quality of workmanship, movement inherent to timber framed buildings, not to mention maintenance (or the lack of it). After all, how many people wash their houses down every six months as is recommended by paint and roofing manufacturers.

Lessons have been learnt and things are now done differently. Will they prove to be successful over the medium to long term, the industry won’t know until we get there.

In the second part of this blog, I will look at some of the science behind the issues and what is currently thought to be the best solutions.


9 Responses to “Leaky Buildings — Part 1 — How did we get here.”

  • Have you seen the 3 part article on the not PC blog? Usually he’s a raving ACToid but his take is interesting, especially on Hardies escaping scot-free:
    Part 1:
    http://pc.blogspot.com/2009/11/leaky-homes-part-1-myth-of-deregulated.html
    Part 2: (more interesting technical details)
    http://pc.blogspot.com/2009/11/leaky-homes-part-2-whats-going-on.html
    Part 3: roundup of comments
    http://pc.blogspot.com/2009/11/leaky-homes-part-3-thought-provoking.html

    Some of the comments are really interesting, others are just the usual idiots.

    • Thank you for the links Owen, they make for interesting reading. Some things I agree with, some I don’t. One thing I would mention is that there are more claddings than just Hardies that are allowing water in and not back out again. My team has worked on some that aren’t a Hardies product, so to bag them alone is not telling the whole story.

  • Interesting… But I always felt there was an element of some pending home owners trying to get ‘more bang for their bucks’ as in a bigger square meter result within their budget constraint.
    Also, lots of section developments in the bigger North Island cities especially, were on filled/re-profiled land with some subsidence being inevitable. Why would you chance a mono clad?
    I recall seeing a home being built locally about 9 years ago, polystyrene ‘cladding’ being put up during a very wet period and sitting uncovered for weeks as it rained consistently. The poly clad is slightly hydroscopic, so can you guess the end result now? Big house though… The owners sold and gone to Aussie a few years ago.

    • In response to your particular points Kevin. It is NZers nature to get the absolute most for their money, however this doesn’t always have a cause and effect on the weathertightness of the building. Admittedly it can be a contributing factor in decisions made, and may have an impact in some circumstances, but overall is not a major factor for buildings leaking, at least from my experience.

      If buildings are built on filled land that subsequently subsides to the point it is noticable, then it doesn’t matter the cladding used. Differential settlement is the problem where one part of the building moves relative to the rest. No cladding or building system can cope with that sort of a problem.

      Building in NZ during a very wet period is an yearly problem, again irrespective of the cladding. If the walls and floors were properly dried out (to below 15-18% moisture content for timber) before they were lined then there should not be significant issues. The issue of expanded polystyrene sheets being hydroscopic is true and is why they soak up water if the exterior plaster coating cracks. However extruded polystyrene is a lot denser and is considered water resistant (to a certain point) when used as a cladding. It certainly performs a lot better than expanded polystyrene.

  • I think the point that notPC was making about Hardies was its chemical reaction between it and the building paper (if I remember right). Also, I think your point about differential settlement: I think that trad weatherboard can cope with that much better than most.

    • Hi Owen. There is no chemical reaction between Hardies and building paper that I am aware of. This is a quote from the notPC blog. “in the presence of wood pulp, building paper plus stachybotrys equals . . . no building paper”. It is the stachybotrys that eats the building paper and is not unique to buildings with Hardies product on it. Stachy grows on any wood based product if it remains wet and is untreated.

      As for differential movement, you are correct that timber weatherboards can withstand more movement than plaster (for instance). However there are many other aspects to a building that cannot withstand much differential settlement at all. Bricks, concrete blockwork, gib board, concrete foundation walls, concrete floor slabs, to mention but a few, all crack and cause problems of various degrees, sometimes within the small movements that weatherboards would otherwise accommodate. Any decisions on the cladding to use should not be predicated on allowing for this sort of movement in a building.

    • Is perfectly fine so long as the bearing capacity of the ground is the same under the footprint of the house. If the ground has been filled (as noted in your first reply) and not adequately compacted then the ground can settle at different rates, or the bearing capacity of the ground may be different. In which case one part of the house may settle a different amount compared to the rest of the house. If this happens then there are bigger problems than just the cladding selection to worry about.

      Certainly I agree that some claddings – like plaster finishes – are less tolerant to movement than others. We have known this ever since stucco houses were built in the 1930s and 40s, as was the Art Deco fashion of the time.

      As always there are many competing factors that influence cladding selection and design features. Ability to accommodate movement is one of them.