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About Tenco
Tenco is one of New Zealand’s largest exporters of forest products. We have built to this position since 1991 when the company was set up to export lumber to growing Asian export markets.  Experience and reputation count; from small beginnings Tenco has become the largest independent exporter of New Zealand lumber and New Zealand’s 4th largest log exporter.  Tenco has a regular shipping program of their own log vessels and in combination with these and other ships currently calls  at 7 New Zealand ports (5 North Island and 2 South Island).
Tenco buys standing forests.  Tenco currently has a number of forests which they purchased at harvestable age to log over a number of years for export and domestic markets.  Tenco also regularly buys smaller tracts of forest to harvest immediately or immature forests to hold until harvest time.  Tenco is interested in broadening  the  base of owners from whom it purchases forests and stands of trees.  A deal with Tenco is a certain transaction.  The owner and Tenco will agree on a value of the tree crop and then Tenco will pay this amount to the owner either in a lump sum amount or on rate per volume unit out-turn from the forest depending on the nature of the tree crop.
Tenco knows there are a lot of farmers who have trees that are close or ready to harvest and will be asking themselves how they should proceed with the sale of their trees.  For some farmers the kind of certain transaction with money in the bank could well be appealing. Tenco is actively interested in buying harvestable forests or trees from areas including all the North Island (except the Gisborne and East Coast districts) and Nelson & Marlborough in the South Island .
If you own a forest in this area (16 years and older) and are ready to enter into this kind of agreement Tenco is interested to develop something with you.
Please contact: 
Work: +64 7 357 5356  Mobile:  +64 21 921 595

NZFFA Member Blogs

Any member of NZFFA can set up their own blog here, just ask Head Office to set one up for you and join the ranks of our more outspoken members...

You can either publish your blogs yourself, or email a document to head office for publishing.

Member Blogs

Recent blogs:

An export log market for "alternative" species?

Dean Satchell's blog
Saturday, November 11, 2017

I had a call a few days back from a guy in Australia looking to source eucalypt logs. On further enquiry, he told me that he represented a big manufacturer in China that required hardwood in large volumes and if we had the resource they'd take it. Shiploads. He was particularly interested in Eucalyptus nitens and E. saligna, but I got the impression they'd take just about any eucalypt. Log specs down to 10cm diameter, he'd pay $10 more per tonne than local pulpwood prices. They're not chipping it either, he reckoned most of it would be peeled.

A few weeks earlier, I also had a call from Australia, this time someone who is exporting cypress logs to Asia. They'd run out of the local native cypress and the market has an insatiable appetite for more. He heard we grow cypress in New Zealand. I believe they use it for coffins, and pine is too "common" to be buried in... cypress being the timber of choice. He was happy to pay "well above" pine prices and would be prepared to take all I could find.

What is happening? I thought the reason we only grow radiata pine in New Zealand was because there are only markets for radiata pine...

Other species apparently with prime export log markets include poplar and redwood and believe me, the minimum log diameter is much less than what any local processor would take.

Now, if I were a real businessman I'd see an opportunity for myself and gather wood for export. But I'm not. My interests are in developing a sustainable local industry around growing and processing specialty timber species for the local market... and I just can't bring myself to put pecuniary interests ahead of that goal. I do acknowledge that having an export market is good for keeping local log buyers honest though, and if we can export what they don't want then all the better for the grower.

We've always been told not to grow "alternative species" unless you appreciate that there will not be a ready market for your logs. Because I don't actually have skin in the export game, I'd be very interested in hearing from anyone out there about what is really happening.

Durability performance and structural timber

Dean Satchell's blog
Wednesday, November 15, 2017

Hazard class H1.2 is an indoor decay hazard, introduced in 2003 as a regulatory reaction to the leaky building syndrome. This standard applies to timber used for structural applications protected from the weather, where there is a risk of moisture content conducive to decay (NZS 3640, 2003). It requires "temporary protection should the wood get wet, through leaks in the building envelope — protection for sufficient time for the leaks to be detected and rectified" (NZS 3640 as cited in Singh et al. 2014b). Hazard class H1.2 also denotes a specified level of chemical treatment, which is a retention of 0.4% boric acid equivalent (BAE) (NZS 3640, 2003).

Durability performance and H1.2

So what level of durability performance should be expected from framing (or structural elements) that become wet and stay wet? The question could be redefined as "how long should we expect the timber element to last without significant decay in this situation, before it is found and remedied". My understanding is that the regulator (now MBIE) has not provided any guidance to industry since introduction of the H1.2 hazard class, this despite New Zealand's performance-based building code that specifies number of years durability required for building elements. All we have for timber framing is that "a 50 year durability is required".

H1.2 boron treatment was introduced to offer "opportunity time" for detecting and repairing leaks. Framing tests undertaken by Scion between 2001 and 2009 resulted in preservative formulations designed to conservatively prevent decay in framing subjected to intermittent wetting (Hedley et al. 2009). Although the concentration of borates required to inhibit brown rot fungi were found to only be "in the order of 0.15-0.25% boric acid equivalent" (Hedley et al 2009), it was decided that because boron potentially leaches in service situations where timber becomes wet, a 0.4% boric acid equivalent level of treatment would be "the cross-sectional retention required to inhibit fungal growth on framing" in the H1.2 specification (Singh et al. 2014a).

This is a simple, clean solution because it provides the consumer with security in the knowledge that they can sleep at night with rain on the roof and drips down their walls, because they have plenty of time to remedy the leak. Perhaps, being satisfied that this conservatively high level of treatment was the only available option, the regulator has never felt it necessary to specify how long framing should last once it gets wet? Certainly I have not been able to uncover any regulatory requirements for this.

To summarise:

  • Perishable wood was not good enough;
  • If more than enough boron is in the timber, then treated timber is unquestionably good enough.

The Reference material

In New Zealand the required level of durability for materials is set as minimum years in service. Timber framing is required to last for at least 50 years. Now, we all know that if it gets wet and stays wet, timber framing will not last 50 years, so proving performance would require some method for verifying durability, a test that measures rate of decay over time and where the tested timber either passes or fails.

The building code is clear that tests need to be relevant to field and service conditions. However, as described by Hedley et al. (2010) "While relative rates of decay in laboratory tests are reasonably easy to determine, absolute times under real-life conditions are considerably more difficult". Therefore, decay rates for any test method should simulate real-life conditions, which will inevitably vary. 

Okay, so why not just compare relative decay rates for other materials with H1.2 boron treated pine as the reference? After all, H1.2 radiata seems to have become the gold standard, the de-facto benchmark with which to compare all others. Well, because the test method would need to meet the requirements as defined in the building code. Unfortunately, we don't have any requirements on how long the wet framing element should last before finding the leak — there is no performance benchmark defining duration of wetness. Perhaps more importantly, because service conditions conducive to decay vary so much, to meet the conditions in the building code a range of tests would be required to establish a set of lab protocols that adequately represents the real-life conditions of a leaky building.

Research by Scion appears not to have followed these criteria i.e. test methods should simulate real-life conditions, using a range of tests. Initial accelerated decay framing tests were undertaken by Scion between 2001 and 2009 using simulated wall units, exposed to an environment that enhanced decay i.e. 25° C, 95% relative humidity and "periodically wetted" (Hedley et al. 2009). Although this method was originally designed to simulate a worst-case leaky-house scenario with "wood exposed to a warm and wet environment containing active decay fungi" (Hedley et al. 2009), what the method revealed was that under these test conditions boron penetrated "into the core of most components in a sufficient amount to control decay" and was found to diffuse "through the whole of the cross section" (Hedley et al. 2009). This experimental design clearly suited boron preservation by aiding diffusion through the wood, without leaching it. The method did not actually simulate the scenario where leaching would be sufficient to reduce protection. I am not aware of any subsequent experiments by Scion that sought to test a range of leak and leach scenarios as required by the building code, although supposedly development of protocols for assessing preservative systems "remains an ongoing activity at Scion" (Singh et al. 2014b).

The Protocols

Hazard class H1.2 testing methods developed by Scion have been introduced into the Australasian Wood Preservation Committee (AWPC) Protocols for Assessment of Wood Preservatives (2015) as the "Wall frame cavity test" (also called the "simulated wall unit test" by Scion) and the "I Frame sample test". For both tests, the protocols state that samples "shall be periodically sprayed with water to maintain the wood moisture content at a level suitable for decay to progress". No further methods are prescribed for how this should be undertaken or how much water to use, or over what time period, but apparently Scion, who undertake such testing for clients, spray their wall unit tests "with water for a short period each week to simulate occasional rain wetting" (Singh et al. 2014b). Another method used by Scion, the "enclosed tank method" involves the tanks being "regularly opened (usually weekly) so that the samples could be sprayed with water" (Singh et al. 2014b). Keeping in mind that the building code specifies that tests need to be relevant to field and service conditions, did the research that led to development of these methods answer the following questions:

  • Given that risk of boron leaching was the rationale for the introduction of 0.4% BAE retention for the H1.2 hazard class, does "spraying with water" sufficiently address that risk, or actually only aid diffusion by keeping the wood moist?
  • How would different methods of periodically wetting boron treated wood affect the retention of boron?
  • What is understood about boron leaching in service conditions and what importance would this have to designing accelerated decay test methods? 

Under their current test methods Scion reports that "periodic wetting helped diffusion into the timber without causing serious loss of boron" (Singh et al. 2014a). I’d note that the "periodic wetting" in this case involved spraying the samples with water 13 times over three years (to keep them moist). Results showed that where timber was surface treated with only 0.22% BAE it was in the same condition after 3 years as timber treated to a retention of 0.42% and 0.65% BAE. Index of condition did not change over the whole 160 week period for all three treatments, apparently because very little leaching occurred from "periodic wetting". Only with low initial retention levels of 0.1% BAE did the wood progressively decay over time under these test methods. What this experiment suggests to me is that concentration of boron determines life of the treated timber rather than how wet or how warm the exposure conditions are. This would indicate that the two key variables that influence rate of decay for boron treated timber are:

  1. initial concentration of boron; and
  2. rate of leaching.

The next step would be to verify or reject this with further experiments. If this were indeed the case, methods for assessing durability performance of H1.2 boron treated timber would therefore need to focus on leaching potential. Unfortunately, it appears to me that methods currently used by Scion to periodically wet the timber only purport to represent wetting cycles as found in leaky buildings. The end result has been a decade where a potentially biased test method has cemented H1.2 boron treatment in place as indomitable, a position currently reflected in both the building code and complete market dominance of that product. Until further experiments establish an appropriate rate of leaching that can be incorporated into design of methods for laboratory tests, the playing field cannot be levelled.

Leaching and boron

So what levels of boron leaching can be expected in a leaking building with wet framing? Is it possible to replicate this in lab conditions and prescribe an appropriate level of leaching? Water flow will be different for every real-life leak situation, as will be resulting levels of decay for boron treated timber. At one extreme is the Scion framing tests and at the other extreme is graveyard testing where the boron quickly diffuses out into the soil and the wood rots. What about the situation where a building leaks, then is eventually repaired, then leaks again in the same place? What about framing in an enclosed situation, saturated with water, and with through-flow of water every time it rains? The only study I am aware of that looked at this used water dosage of 100ml per lineal metre of framing every four days, with the conclusion that on average boron reduced by approximately 30% over the first 6-8 months of the testing (Drysdale et al. 2011). This suggests that further work is necessary on replicating real-life service conditions.

Questions in my mind relevant to field and service conditions are:

  1. Does dripping water induce leaching in wet boron-treated framing?
  2. If so, how does rate of dripping and period of dripping affect boron levels in wet framing?
  3. How rapidly can boron deplete if leaching does take place?

Assuming that different leaching scenarios will affect the durability performance of boron-treated timber, leaching rate would need to be introduced into the equation before H1.2 boron treated radiata could be the reference material (experimental control) for any comparative lab testing procedure. Keep in mind that the rationale for such a high BAE content (0.4%) in the first place was as an insurance policy, a redundancy, not for the specific level of durability performance attained by 0.4% BAE in wood that is only "periodically wetted" just to keep it moist. 

It also needs to be kept in mind that with fixed preservatives or naturally durable timber, that one would expect little variability related to water flow, with moisture content and temperature being the important variables. 
However, even if a fixed preservative were to be used as the reference material, the cart should not be before the horse. The preservative formulation for the control would need to be set at the level of treatment that meets the predetermined durability criteria, that being a defined duration of wetness (which is the time it should reasonably take to find and remedy a leak) along with an index of condition expected after that time. H1.2 boron treated timber has an index of condition above 8 even after ten years of exposure in Scions accelerated decay test units (Page et al. 2011), so what does that tell us? Is the level of treatment excessively high or is the boron just not being leached? Is this an appropriate method and reference material for other materials that are seeking to conform with the performance-based requirements of the building code?

Regarding some kind of benchmark performance, what is an appropriate index of condition? Singh et al. (2014) found that only when the decay condition reached moderately severe (ratings 6 or lower in the AWPA scale, standard E7-93) did timber stiffness suffer. What level of decay is acceptable to the regulator for a defined duration of wetness, under accelerated decay test conditions? Is this just a subjective call made by Scion staff for client applicants to present to Standards committees (or Codemark) for approval as acceptable solutions under the building code, or should the criteria be set by the regulator?

Natural durability and the Reference material

The AWPC protocols specify test methods for assessing performance of preservative treatments. I have no objections to using these test methods for comparing different diffusible preservatives in wood. Leaching is not important when comparing equally diffusible preservatives. I also do not see why different species, each treated to H1.2 boron retention, could not be compared with a radiata H1.2 reference material using these methods. I'd expect that to be species independent anyway.

There is also no doubt that the Scion accelerated decay frame unit test as defined in the AWPC protocols is highly effective in determining relative durability of untreated timber or fixed preservatives, because conditions are highly conducive to decay (i.e., warm & wet). Fixed preservatives might even be compared with naturally durable timbers, but what would be the reference material? Untreated radiata developed severe decay in only six months and components were beginning to fail after only 12 months (Hedley et al. 2010), so radiata pine is clearly not a very suitable reference material. Perhaps Douglas fir heartwood could be the reference material that would satisfy the regulator as being sufficiently durable for framing? Hedley et al. (2010) found that Douglas fir heartwood lasted between 3 and 6 years before decay was unacceptable in the accelerated decay model frame units. Anyway, my point is that apples should only ever be compared with apples. If a suitable reference material were available that represented the level of durability that the regulator requires, then this should be the reference material for comparing other naturally durable species and fixed preservative-treated timber against. In contrast, coming up with a fixed preservative retention level that is arbitrary but more then adequate, then expecting naturally durable timbers to match or exceed that arbitrary performance level is the cart before the horse. 

Although Mick Hedley's original intention was to set up a method for testing materials under accelerated conditions, researchers who subsequently picked up his pioneering methods have never looked beyond the assumption that the leak scenario was adequately represented by "intermittent wetting" as prescribed in the original experimental design. Previous studies have shown that extensive loss of borates occurs only when timber remains wet throughout its cross-section (Obanda et al., 2008, as cited in Singh et al. 2014a) and where there is a sink for boron migration (Lloyd, 1995) i.e. leaching takes place. Where there is little leaching as per the Scion frame test, 0.4% BAE is significantly more preservative than is necessary to achieve 5 years or more decay prevention. So has duration of wetness become the horse, with H1.2 treatment being the cart?

The question remains: How many months or years should wet framing remain free of decay before the situation is discovered and remedied? The NZ building code is, after all, performance based and durability is defined as years in service, not a treatment level.


AWPC Protocols, September 2015
Drysdale, J. Marston, N. Hedley, M. (2011) A Method for Studying Boron Redistribution and Leaching in Timber Framing. IRG/WP 11-20476
Hedley, M. (2005) The decay resistance of Douglas fir, macrocarpa, Lawson cypress and European larch framing. Summary of results after 52 weeks exposure. Report prepared for the Building Research Association of New Zealand. Scion, Rotorua.
Hedley, M. Page, D. van der Waals, J. (2009) Application of Boracol 200rh (Framesaver) to control decay on pre-decayed model frame units. Wood Protection Issue No. 43.
Hedley, M. Page, D. van der Waals, J. (2010) Summary of Tests on Untreated Douglas-fir, Treated and Untreated Radiata pine for Use as Framing in Domestic Construction in New Zealand. Report No. FFR- DS029
Lloyd, J.D. (1995) Leaching of boron wood preservatives - A reappraisal. B.W.P.D.A. Annual Convention 1995.
Page, D. van der Waals, J. Singh, T. (2011) Decay Resistance of Radiata Pine Framing The Condition of Test units after Ten Years Exposure. Scion.
Singh, T. Page, D. Bennet, A. (2014) Effectiveness of on-site remediation treatments for framing timber. International Biodeterioration & Biodegradation 86, 136-141.
Singh, T. Page, D. van der Walls, J. (2014b) The development of accelerated test methods to evaluate the durability of framing timber. International Biodeterioration & Biodegradation 94, 63-68.


Disclaimer: Personal views expressed in this blog are those of the writers and do not necessarily represent those of the NZ Farm Forestry Association.

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