Archive 2010

How Building Standards Have Changed Ken Collins Oct 04


With the recent events in Canterbury and Invercargill it looks like the building standards in NZ will again come under close scrutiny.

The suitability of our standards is a valid question and response, especially when our knowledge has recently been increased by the Earthquake and the collapse of the Invercargill sports stadium roof.

The first design standards for earthquake loadings on buildings were introduced in 1935 following the 1931 Napier earthquake. Since then, significant advances in the required design standards have been made with major changes incorporated in 1965 and 1976.

Even more recently the structural design standard NZS 4203:1992 was replaced with NZS 1170 in 2002, with part 3 and part 5 added in 2003 and 2004. However NZS1170 has only been mandatory in the last couple of years, with engineers able to use either 4203 or 1170 up until then.

Certainly the requirements in 1170 are far greater than 4203 and this has increased building costs by quite a bit as additional structure is required to resist wind, snow and earthquake loads.

Previous Lake Angelus Hut

Previous Lake Angelus Hut

As a practical example of the changes over the years, we were involved in refurbishing a reinforced concrete church built 50 years ago. The Structural Engineer doing the assessment was impressed that the building had been well overdesigned for when it was built.  Possibly at 1.5 to 2 times the earthquake strength required for its day.

Despite this the building still only came up to 65% of the current requirements in NZS 1170. However this building is still not deemed to be an earthquake risk, which is set 33% or less of the current standards.

On this basis, the structure required to resist earthquake loads has increased about 4 fold in the last 50 years.

Angelus Hut under snow

Angelus Hut under snow

Similarly when you look at the requirements for wind and snow loads, some clients have been surprised at what is now being required. We have designed tramping huts to replace some old ones built in the 50s and 60s. Some of these are in high alpine areas with significant loads being imposed. (See the photo below, where there is only 500mm of the roof ridge sticking above the snow, the rest of the hut is completely under snow).

When you look at the existing hut, which has survived storms and the harsh environment for 50 odd years and is still sound, and you see how little timber was used to hold these things together, you wonder how the old buildings survived. Especially compared to the new buildings where there is significant bracing, and timber structure required.

Unfortunately the Stadium Southland failure is a stark reminder of what can happen. I suspect that it will be some time before the full details of what went wrong will be known, and it will be a combination of factors the contributed to the failure.

With snow it is a combination of factors as to how the load gets imposed. Roof shape and slope, the shape or geometry of the structure, the strength of the connections, the types of materials used, the amount of snow, and how long it is there for, all contribute to how well the building structure as a whole performs. It may be that the building was designed to the previous standard, which was deemed suitable 5 years ago, but as we have seen, what was acceptable years ago is now no longer.

New Angelus Hut

New Angelus Hut

Thanks to nature, we now have some real live examples to test the theory and assumptions against. Our building standards will continue to evolve and change as our knowledge improves, and as we have more ’learning experiences’. However it does occur to me that no matter what we do we can never be 100% future proofed against nature.

You can build to resist the shaking induced by the ground acceleration of an earthquake, but you can’t build to resist the ground moving by even 300mm. As we have seen in Canterbury, if the ground doesn’t just shake but permanently shifts up, down, or sideways, it will tear your building apart.

Initial Thoughts on the Canterbury Earthquake Ken Collins Sep 06

Deans Homestead

Deans Homestead - Photo from

The big earthquake in Canterbury last weekend has certainly reminded us just how shaky our isles are, in dramatic fashion. While our thoughts are with all of those affected, and we are all grateful that there has been no loss of life, the quake has exposed — very graphically — just how buildings react to a big shake.

For many years the bracing and structural requirements for buildings in New Zealand have been increasing. As new research is carried out, so the values that our buildings need to meet have increased. Our scientists have also created world leading developments. (I was going to say ground breaking developments, but that isn’t quite appropriate at the moment). Dr Bill Robinson created the base isolators used on many important buildings both here and overseas, as an example.

However, the location of this quake has certainly surprised many scientists. Certainly the current NZ Standard for light timber framed construction (NZS 3604) that is most often used for building houses, shows that Christchurch is a medium earthquake zone, while Lyttleton and Timaru are in a low earthquake zone. I suspect that the current review of NZS 3604 will be reviewed again as the results of this quake are analysed.

Obviously it is far too early to draw conclusions as to the technical details of what has happened, however initial observations from the photos and news reports show that there are some things you can plan for, and others you can’t.

It is pleasing to see that many of the buildings that have been earthquake strengthened have survived mostly intact. You are never 100% sure how well any remedial work will perform. Now that it has worked it is a pleasing result. Plus any failures will add to the knowledge base on what needs to be done better next time.

As would be expected, the buildings with the greatest damage are those built using un-reinforced double or triple skin brick construction, or even solid stone construction. This is a common form of construction in England, however it is not such a good idea in shaky NZ. Unfortunately many of these buildings were also regarded as some of our historic heritage, and now they are lost forever.

While a great many buildings have survived with minimal damage, the things you can’t plan for are where a fault ruptures the ground directly under your building, or (to some extent) where liquefaction turns the ground to quicksand.

While most buildings have coped with the ground shaking (to greater or lesser degrees), it is where the ground has moved differentially and permanently that has torn some places apart. You can see where the ground has moved sideways. It has opened up in a crack or heaved up in a mound. What were straight fences now have a 2 metre offset. And so, it is that sort of an offset, when it opens directly under you that is catastrophic for any building. Science does not know where these will appear and there is no way to plan or avoid this sort of action.

Liquefaction on the other hand has had a lot of research done into how it happens, and the types of soils that are susceptible to it. The images of buildings having subsided with large areas of sand around them, and residents reports of water gushing up from the ground all indicate that this was the likely cause of the damage.

The GNS Science web site describes liquefaction occurring when – ’water logged sediments are agitated by seismic shaking. This separates the grains from each other, reducing their load bearing capacity. Buildings and other structures can sink down into the ground or tilt over, whilst underground pipes may rise up to the surface. When the vibrations stop the sediments regain their solidity once more.’

There are known techniques for reducing the likelihood of a building sinking in such an event, however relating the known science to a specific piece of ground is not as exact as many would like. For example it is suspected that because much of the Hutt Valley (in Wellington) is on old river planes, these areas will liquefy in a big shake. Many buildings therefore have piles extending down through the river gravels and onto hard rock.

However, what isn’t fully known is how big a shake it will take for the ground to liquefy, to what extent it will happen, what the exact areas of soil that will liquefy are, or what extent of structural work is required to  mitigate the effects.

Again, it would appear that because Christchurch was not previously assessed as a high earthquake risk, then some areas that were built on were not expected to liquefy as they have.

As the clear up and the rebuilding begins, look for numerous reports in coming months as the scientists describe what has happened, and the engineers look for ways to counteract the awesome forces created by moving ground.

Building Materials That Kill Bacteria Ken Collins Aug 23


In an effort to control the spread of bacteria (that are harmful to humans), the science world is always coming up with some interesting innovations. This now includes additives to building materials that will kill bacteria, including the dreaded MRSA strain.

Antimicrobial, antibacterial and antifungal powdercoating has been available commercially for a few years, and now scientists have developed an additive for paint that targets only staph bacteria.

The innovation comes in how these materials can provide lasting protection, despite some surfaces like door handles and handrails getting a lot of human interaction.

In the case of the powdercoating, the manufacturers have added silver ions to the powder coating material and found a way to keep the ions distributed through the coating once it is applied and heat fused onto the (typically metal) substrate. Powdercoating is often used as the aesthetic and protective coating on metals, such as handrails, door handles, window and door frames, furniture frames, equipment frames, etc.

Silver in various forms and silver ions have long been known to act as a natural antibiotic, dating back centuries, although it has fallen in and out of favour over time as medical knowledge has changed. The silver ions interrupt the replication ability of proteins within the bacteria, making them inactive. Having done testing for effectiveness and gaining US FDA and EPA approvals for food contact, the company that makes this powdercoating is now promoting it for use where ever you want to stop the possible spread of bacteria.

The paint additive, was discussed here and is reported to kill MRSA without the use of antibiotics. Using carbon nanotubes bound with lysostaphin, it is the lysostaphin that does the damage.nn-2010-00932t_0006

The report identifies that lysostaphin is a naturally occurring enzyme used by non-pathogenic strains of Staph bacteria to defend against Staphylococcus aureus, including MRSA. Lysostaphin works by first attaching itself to the bacterial cell wall and then slicing open the cell wall. That means it’s a highly-targeted substance – in fact, it only destroys staph bacteria.

This looks to work well in the lab, but it has yet to be turned into a commercially available product.

Although we have had fungicidal paint for some time, and it is sometimes used in high humidity areas, the concept of using building materials, or in this case entire wall surfaces, to act as an anti bacterial agent is certainly an interesting development.  On the face of it the advantages could be many, especially if it means that the building environment is helping to reduce the number of places harmful bacteria can sit and be transferred from person to person.

However, a concern that has been expressed is the evolutionary process, where we have already seen bacteria become resistant to some commonly used antibiotics. If these products are widely used, will bacteria evolve to become resistant to the active parts of these building products? Only time will tell.

Fit for Purpose? Ken Collins Aug 05

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This recent article on The Herald web site highlights how careful we all need to be when trying to contain things in a secure laboratory environment. While I don’t know the specific details of this particular facility or the event that was investigated, it does highlight that the success of any laboratory is the interaction between the buildings features and the procedures used to operate it.

All scientific buildings need to be built toAM120 low res minimum standards, and depending on the use of the building, those standards demand different features to be incorporated. However, to ensure that the building provides the environment needed, the management regime needs to be carefully considered to ensure the correct features are provided.

A couple of illustrations to demonstrate this.

The standard says all surfaces must be able to be wiped down with disinfectant. If the operating procedure calls for the use of a typically used, every day product then the walls, floors and other surfaces can be made of relatively standard materials, so long as they are smooth and water resistant. If on the other hand the operating procedure calls for the use of a strong alkaline solution at very high temperature, then the building and the fittings need to be constructed of entirely different materials.

As another example, the standard says the lab needs to be fumigated. If the management system determines that you are going to close off that area and clear out all people, then the building features are relatively straight forward. If on the other hand you want to be able to keep staff working in the adjacent room, with a pressure differential between the rooms, then the building structure and the mechanical plant required is significantly different.

Although both systems are suitable for the same science being done, one is significantly more inconvenient and time consuming than the other. One is also cheaper than the other.

You can then see the potential problems where you change the management system later on, and the building environment may not cope too well.

It is equally true in the reverse, where a time consuming or limiting operating procedure could be significantly improved by changing some of the building features, so as to allow greater ease of use.

It is human nature to take short cuts where an operating procedure is overly complicated or an impediment to doing their work.

Therefore a comfortable balance needs to be struck of features, environment and usability. Careful consideration of (what usually boils down to) cost vs benefit needs to be taken during the design stage of any new or refurbished facility. It also needs just as much consideration when changing the use of an existing facility. Especially when you consider the total life cycle costs and operational costs.

For any scientific facility to be successful, the building needs to have the right features, that match how it is going to be used. Then these two together need to be suitable so that the users are able to (and want to) do their science (work) in that way.

Intelligent Buildings? Ken Collins Jul 12

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Modern buildings have a lot ofmarine-lab-energy-diagram technology that goes into them. From the development of the products they are built from, to the systems that allow us to live, work, and play in them. The rate of technology uptake into our new buildings is surging up every year, especially when it comes to entertainment systems and power control.

However one area where the uptake has been lagging, is automation of the building itself. There are many — mainly commercial buildings — that have computers to control heat and ventilation, opening or closing louvers automatically, not to mention air conditioning systems with some advanced control systems.

But it was this article on an “Intelligent house” that caught our eye in the office. Extending the technology interface between building and control system where it features a prototype climate control system with sensors in the floor and walls to measure the temperature. The information is sent to a server, which can then open or close windows to keep the temperature comfortable. The system is also connected to a weather station which can predict the weather for several days.

To see these features being built into a house is unusual, and the climate control system is described as being a prototype. But why is this? Why (on the whole) is this sort of technology not being developed and marketed widely as the next step up from passive insulation and energy efficient heaters?

The article doesn’t indicate what the cost of the system is, although I imagine if it is a prototype, it won’t be cheap. All home owners look for the payback on anything more than the minimum, it is possible this system has a very, very, long payback.

Or could it be that the idea of a computer controlling parts of your house, including opening and closing external openings, is at odds with our ideas on security, and our fears of someone being able to hack in? (Both in a digital sense and the good old analogue way with a crowbar).

May be we just don’t like the idea of closing all the windows, leaving the house, walking back in and opening the windows again, every time something goes wrong with the system.

What ever the reasons, there is still along way to go with technology integration into our buildings, and more specifically our houses. And the integration of the various independent systems into a unified system.

Houston — You have a problem….. Ken Collins Jun 25

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It’s nice to know, well actually a little worrying to know, that New Zealand building owners aren’t the only ones to neglect maintenance work on their buildings.

A recent article in New Scientist Magazine (15679px-Aerial_View_of_the_NASA_Ames_Research_Center_-_GPN-2000-001560 May 2010) had a small piece on the problems faced by NASA. Yes, even the best let their major assets deteriorate.

With NASA again expected to develop new technologies for space flight, a report to the US National Research Council identifies that may of their labs, including wind tunnels, need repairs and upgrades. With the exception of a new science building at Goddard, over 80 percent of the research laboratories at these facilities are more than 40 years old and need significant annual maintenance and upgrades. Some apparently don’t even have adequate electricity or heat. Clearing the overall repair and maintenance backlog is estimated at US$ 2.46 billion! Up from US$ 1.77 billion in 2004.

Another posting at discusses the issues here.

Closer to home……

A BRANZ study in 2005 into the condition of New Zealand housing stock showed that in order to repair and maintain significant defects an average of $3700 per house was needing to be spent. With between 1.5 and 1.6 million homes in NZ at that time, the total repair bill would be about NZ$ 5.7 billion.

Leaky Buildings — Part 2 — What we now know Ken Collins Jun 08

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Following on from my blog on Leaky Buildings – Part 1 -and how we got to where we are, this blog covers some of the science and research that has gone into the building industry as aponding water lounge roof result.

At this stage I must point out that there are other people with specialist areas of knowledge and research, in what is now quite a wide topic.  So, as blogs tend to be, this is more of an overview from my experience, rather than a detailed technical paper.

With all buildings that have ’leaking’ issues, the problem is that water gets into an area it shouldn’t be (most commonly the structural timber frame), the water stays there because it can’t drain or evaporate away. When the timber remains wet (typically above 30% moisture) and relatively warm, these conditions allow fungi to grow, which rots the timber.

The ways that water gets into a building falls into 4 broad categories, with many iterations in between where a combination of these forces are at work.

Gravity: generally a hole that water drips into, or where water is flowing down a cladding (or a flashing) that doesn’t adequately direct the water away, out of the building fabric.

Capillary Action: where water in the ground is soaked up by building materials (including DSC01305concrete) and transferred along to structural elements over time. This is commonly what is referred to as rising damp. It also happens where water is allowed to pond and hydroscopic materials are soaking in it (or close enough for rain splash to soak the material).

Condensation: the interior of your house is full of water vapour. From cooking, showering, laundering, un-vented gas heaters, and your own hot breath. If this vapour isn’t extracted or vented out of the house then it can condense on cold surfaces. Such as you see on your windows in winter. This also can happen inside your wall if the conditions are right.

Air Pressure: or more specifically a pressure differential. When it is windy there is a higher air pressure on the outside of the building than the inside. This in effect sucks air through any holes, cracks or openings. If it is raining then the water is taken in along with the air flow.

If you think about all the things that can happen in and around our buildings, the number of ways water can get into our buildings are too numerous to mention. It also follows that just because water has got into a building doesn’t mean it is a ’leaky building’ as such, which commonly implies a cladding failure.

The action (or in-action) of owners has always been an issue. All buildings require regular maintenance, and sometimes a bit of good old fashioned TLC is all that is needed to keep the building water tight. A recent article on the Beehive roof leaking is a perfect example of this.

Another classic is for gardens to be built up around the house. If the sub-floor vents are covered this significantly reduces the sub-floor ventilation and the water coming out of the ground under your floor isn’t removed, allowing sub-floor framing to remain wet. If the bottom of the cladding is buried in the soil (or even too close to the ground) then this will allow water to easily wick up into the framing.

There are a number of variables and reasons for condensation to form inside a wall cavity. Relative humidity, air pressures, vapour pressures, and temperature differentials all contribute to where the Dew Point is. This means that in certain circumstances water vapour could be condensing on the timber framing, inside the insulation, on the back of the cladding, or even on the building paper. This is a known cause of some so-called leak problems and rotten timbers.

When people talk about ’Leaky Buildings’ the most common image that comes to mind is of water getting into the timber framing, through a hole in the exterior cladding, and that timber remaining wet. In the early days of the current leaky buildings problem, existing brick veneer and cavity stucco designs were simply adapted to a wider range of claddings. It was recognised that if (when) water gets through a cladding, a cavity between the cladding and the building paper which is attached to the timber framing allows it to either evaporate or to drain away.

Further research has also shown that the reason for this is that cavity helps to equalise the Window-detailsair pressure behind the cladding, and the lack of air flow allows water to drop out and drain away. But of equal importance, it has shown just how effective a cavity is at allowing any moisture to dry out. BRANZ released initial results of it’s research in Build Magazine in June/July 2007.

They found that water dries 100 times faster from the back of the cladding than from inside timber framing, mainly due to how fast water diffuses through timber. When you add in that we are demanding higher levels of insulation and air tightness in our buildings, the ability for wall framing to dry out is further reduced. This unwanted water then tends to evaporate and condense repeatedly until it soaks into the wall materials or migrates inside the building.

The dilemma we now face is now how to allow for air movement and moisture drainage in a wall while still maintaining a high level of insulation. A cavity behind the cladding allows for ventilation and a drainage path, but it also decreases the insulation value of the wall. So more insulation is shoved in the wall, reducing the ability of the wall to breath even further.

The BRANZ research also highlighted what a significant part air pressure has to play in leaks. The Acceptable Solutions to the Building Code requires that all window and door frames be fully sealed to the structural timber frame to eliminate the air leakage path around these openings. Testing showed that even a small gap in the sealant had a big impact on air flow, and the water it carries. So the important thing is for the cavity behind the cladding to remain at an equal air pressure to the outside. In effect the cladding is now acting as a rain screen, rather than trying to achieve a waterproof membrane.

The truth is that we have ‘thought-built’ buildings. We always have had this, and it is even more so now. To build houses the way we do (in New Zealand) requires knowledge, skill and understanding. Construction clearly requires the designer, inspector, and builder to work from the neck up. They need to think as they draw, observe, and install the building components, like flashings, building paper and claddings. Thinking about where water will be coming from, and where it’s going to go. Miss something and the whole stack of cards can come down.

This is even more so with the rise of ’cladding systems’ where the one manufacturer provides all of the flashings, fixings, and finishings. Even good old fashioned things like weatherboards and bricks are starting to fall into this category. You now need detailed knowledge of how to install a particular system to make it work. Specialist installers, trained by the manufacturers are growing in number. On a recent project there was even a company who specialised in installing just the sealant between the windows and the timber framing. Almost gone are the days of generic claddings where you could use what ever individual components you liked and the whole thing still worked.

This obviously isn’t the be all and end all of this problem. There is a lot more to be learnt about how our buildings work in our environment. We are already seeing that some supposedly remediated buildings, aren’t, and they are leaking again. The story still has some way to go — unfortunately.

Earmuffs in Pre-school? Ken Collins Jun 01


I had promised the next blog would be my second part to the Leaky Homes blog, and it is on its way. However, this article in the Dominion Post caught the eyes of the team in our office.

Do we really need to put earmuffs on our pre-schoolers when they are at Playcentre or other Pre-school facilities?

While the intentions are admirable, to minimise any hearing damage to our wee youngsters in noisy environments.  The people in our office thought earmuffs in pre-schools was going a bit far.

We have recently been involved in refurbishing some pre-schools and assessed the issue of noise as a part of the design solution. As a result we had sound absorbing materials installed on the ceiling and on walls. Sound absorbing vinyl flooring is also now widely available, not to mention that carpet is also a good sound absorber. The location of activities was also considered.

Once the work had been completed there was a significant difference to the sound levels in the kindy, although we weren’t able quantify the difference without the use of a sound meter.


So, while we agree that everyone (including the little ones) should wear hearing protection when engaged in noisy activity, like using power tools, watching motor racing, etc, we also see that good building design and selection of materials can create an environment that reduces potential problems.

Surely children wearing earmuffs in a pre-school would severely affect the way the teachers could interact with them, and in turn create a host of other problems? We see that it is far better to create an environment that is fit for people rather than the other way round.

Leaky Buildings — Part 1 — How did we get here. Ken Collins May 20


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.

Timber treatment: what are the best options? Ken Collins May 11


timber treatment 2Some time ago there was a lot of media coverage on the use of CCA (Copper Chrome Arsenic) timber preservative. This caused a number of our clients to ask for alternatives, so we did a little research into what the implications are.

Pine needs to have large amounts of preservative to stop it rotting when in contact with water, and especially in ground.

There are two alternatives to CCA commercially available: Copper Azole based (CuAz) and Alkaline Copper Quaternary (ACQ). Both rely on very high concentrations of copper to act as an agent against fungal and insect attack, and as such both are strongly alkaline.

Unfortunately this also means that these products are very aggressive to mild steel and even galvanised steel. The Building Research Association of New Zealand (BRANZ) did some testing and found that in comparison to CCA treated timber:

  • In timber treated to H3.2 (the treatment level for timber in occasional water contact, often used in exterior wall framing, in wet areas, and outdoors above ground contact like decks), mild steel corrodes at rates of up to 5 times in CuAz and ACQ preservative.
  • In timber treated to H5 (the treatment for timber in contact with the ground, eg floor piles, structural posts, and fence posts), mild steel corrodes at rates of up to 12 times in ACQ preservative. (you can’t get H5 treatment in CuAz).
  • Galvanised steel corroded at a slower rate than mild steel, however the corrosion rate of galv steel in CuAz and especially in ACQ was still significantly higher than in CCA treated timber.
  • 316 Stainless Steel performed well in all the preservatives with minimal differences in corrosion rates.

A copy of their Conference Paper is available here and the more in depth Study Report can be found here.

timber treatmentIn short this means that if you use the alternatives to CCA then all the fixings (nails and screws), bolts and brackets (in-fact anything metal) that touches the timber must be 316 stainless steel or powdercoated. Consideration also needs to be given to the use of stainless steel flashings as well, because even water runoff from ACQ and CuAz treated timber will corrode mild steel, aluminium, and galvanised steel..

What ever you do, there is no current solution to preserving timber without using large amounts of heavy metals and toxic chemicals. But in saying this, you would have to suck on a lot of logs (or wood chips) to leach enough of the chemicals out of the timber for it to have a measureable effect on you. This includes CCA treatment.

So, unless you are building a children’s play area and have particular concerns about children eating the wood, CCA treated timber is still the best to use for the construction of buildings in NZ, especially where you need to treat to H3.2 or above. Not only for cost, but also because of serious durability concerns raised by the BRANZ testing.

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