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Determinations, specialty timbers and the building code

Dean Satchell's blog
Monday, July 10, 2017

What do you know about "Determinations"? Well... Determinations are best described as judgements made by MBIE where disputes arise between the Building Consent Authority (BCA) and those undertaking building work. BCA's must accept compliance where the building work is an "Acceptable Solution", such as when using materials complying with the standards referenced in the building code. However, where building work doesn't "fit" within these constraints (such as using materials that are not specified in the standards) the owner has to apply for an "Alternative Solution".  

Last year an application was made to Marlborough District Council for specifying NZ grown European oak for flooring, floor joists and beams in the owners dwelling. This was an Alternative Solution because oak is not a species listed in NZS 3602 "Timber and Wood-based Products for Use in Building". MDC rejected the application because they contended that they didn't have enough information on the durability of European oak for use in internal applications.

Yep, true...

The owner had to supply a whole lot of information on the natural durability of oak to MDC, for use in a dry internal environment. Now, keep in mind that the natural durability of oak is the stuff of legends and is based on many centuries of use as a structural timber. And yes, this is a true story, MDC declined the consent because they asserted that the applicant didn't supply enough information on durability.

The information supplied included:

  • A paper published in the New Zealand Journal of Forestry: “Durability of New Zealand grown timbers”
  • Information about oak indicating the timber is classified as “Durable”.
  • Email correspondence from a Scion Research scientist saying "results indicate that the heartwood has a durability rating of 2 (durable) in ground contact. The heartwood is generally regarded as durable - very durable in Europe hence there should be no problem with it being used for framing timber or for flooring."

The owner was forced to apply to MBIE for a Determination to sort out this mess. They just wanted to use oak timber in their house! 

What was in question was the durability in a dry internal environment. The Determination is eight pages long and is all very official, but concludes that "New Zealand grown European oak in its proposed use as flooring, floor joists, posts and beams in an internal double-height space in the building will meet the requirements of the Building Code with respect to Clause B2 Durability."

Unfortunately, next time a BCA declines an application to use oak for similar applications, the owner will need to go through this process all over again, because this Determination only applies to that one house - Determinations are conducted on a "case-by-case basis".

Is there a solution to this mess, where "alternative" species are no longer relegated to the realm of "Alternative solutions", so that ignorant BCA's no longer get away with being completely unreasonable? Did you know that laying a blackwood floor currently requires an Alternative Solution and is open for rejection by your local BCA?

We need to make it easier to use specialty timbers in building work where they are well suited. This is why I'm representing Farm Forestry Timbers on the NZS 3602 committee "Timber and Wood-based Products for Use in Building".

Stringing Up the Stringybarks

Denis Hocking's blog
Saturday, July 08, 2017

The stringybark eucalypts were identified some years ago as a promising group for solid wood production in New Zealand with a combination of good growth rates, early heartwood formation, relatively few forest health issues, relatively easy sawing and processing with less growth stress than many species plus ease of drying, and finally good wood properties combining strength, stability and good durability for above ground uses. More than a dozen species all have very similar timbers while offering some differences in site tolerance, especially frosting. Another plus is that they thrive on lower fertility sites. The new uncertainty today is, I guess, how they handle myrtle rust in our environments as monocalypt eucalypts are recognised as being generally more susceptible than symphomyrtus species.

This enthusiasm for stringybarks was seen in the farm forestry stringybark trials established more than ten years ago, though I have not seen any recent analysis of the current status of the trial.

I have been an enthusiastic stringybark advocate for many years after discovering, in the ‘80s, how well they performed on my sand dunes. This was somewhat contrary to the official advice of the time I might add which recommended “moist, fertile, free-draining sites”. I do agree with the last recommendation and I might add that monocalypt eucalypts generally do seem to be more drought sensitive than symphyomyrtus species, but fertility is definitely optional. Oh, and they can be grown a long way south of Northland contrary to opinion of the ’80s.

My problem with current work on the stringybarks is that in my opinion the focus is on the wrong species. While we need more than one species to cover our different environments, especially frosting, resources are limited and so there tends to be one focus species. At the moment this would seem to be E. globoidea, (white stringybark) but I think it ought to be E. muelleriana, (yellow stringybark). Why?????

  1. Well I will be very honest and admit some people will see some self interest here as E. muelleriana is easily the best performing stringybark on my sand dunes. But you also find big, healthy old E. muelleriana popping up in odd corners round the Manawatu/Whanganui region. People who attended the logging demonstration day at this year’s conference may not have realised that there are some impressive 60/70 year old E. muelleriana amongst various other species, E. fastigata, E. saligna etc. in a Euc. stand they probably noticed on the way up to the logging site in Grenock Forest. E. muelleriana might not be the best performer on all sites, but it is certainly impressive on many sites.
  2. However one of the main reasons I got onto E. muelleriana was its reputation for high quality timber, perhaps best summarised in Keith Bootle’s all-encompassing tome “Wood in Australia: Types, Properties and Uses”. He describes E. muelleriana as “Probably the best of the stringybarks for wood quality” (p 348 in second edition). In support of this I would note the Davies-Colleys’ enthusiasm for the species and also the furniture tutors at our local polytech UCOL, who consider it probably the best working timber of the 6-8 eucalypts species I have supplied.
  3. In my experience E. globoidea has never matched E. muelleriana for growth or form on my sites with quite a number of dif- ferent seedlots. A year ago, through contacts with Paul Millen and the DFI, I supplied some E. globoidea logs to Nelson Pine for rotary peeling and LVL trials. A lot of technical data was recorded in the process by Canterbury University students. It was a hell’uva long way and an expensive truck trip to come for some rather uninspiring logs, that apparently didn’t perform especially well. I was very keen to see them take some same age E. muelleriana logs that would have been larger diameter, straighter and quite possibly, in view of those superior wood properties, might have peeled better. But no, it had to be E. globoidea.
  4. So what does E. globoidea have in its favour? I know the breeders think it has more potential because of its greater genetic diversity. It is undeniably genetically diverse, and I well remember the late Ian Brooker, during his late 1990's visit here, suggesting someone needed to spend 6 months sorting out the white stringybarks because there are probably several species buried under the current labels. If you are starting behind the competitor regarding wood properties and you are breeding with essentially different species, there may be some delay in producing a reliable winner as you move through hybrids, that should have the advantage of hybrid vigour, and then have to breed back to a consistent phenotype. Another alternative might be vegetative propagation of selected hybrids, but that also means more work and expense to develop systems. And if you are dealing with hybrids, why not hybridise with other stringybarks species.

There are also claims that E. globoidea is more durable than the other stringybarks. I am not convinced of this. The gold standard for durability of Australian timbers is probably Thornton et als’ Forestry and Forest Products Report No: 1475. Unfortunately E. globoidea wasn’t included in their graveyard tests, though the other white stringybarks E. eugenioides and E. eugenioides (Wilkinson’s stringybark) were and they were upper class 3 durability along with two other stringybarks including E. muelleriana. Bootle lists all stringybarks as class 3 in the ground and class 2 or 3 above ground, with E. globoidea and E. muelleriana both listed as class 3 in the ground and class 2 out of the ground. I might add that this tallies with my experience. You could certainly breed for higher durability, but if you also want good growth rates, superior form and early heartwood formation progress may be slightly retarded.

So my plea is “let’s hear it for E. muelleriana”. I am sure there will be many opinions out there, possibly even some that agree with me.

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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