Specialty Timbers New Zealand

NZFFA Member Blogs

Member Blogs

• Dean Satchell's blog
   
• Eric Cairn's Blog
   
• John Fairweather's blog
   
• Murray Grant's Blog
   

---

Recent blogs:

Natural durability, accelerated framing tests and relative durability

Dean Satchell's blog
Sunday, August 22, 2021

Laboratory Tests can be used to study rate of decay for materials, but their perfomance must be assessed for "relevance to field and service conditions". Thus a correlation is required between accelerated laboratory "test" decay and rate of decay that occurs in service. On the other hand, Similar Materials Tests compare relative decay between two materials, the one being tested against the one with a proven performance. 

Below (Figure 1) are results from a Similar Materials Test undertaken by Scion. The controlled conditions provide an environment that enhances decay, to compare relative decay between species in an accelerated time frame. Absolute rate of decay is not important, what is important is whether the relative durability of the test material exceeds that for a "reference material", i.e. one with a proven level of performance.

What is important to understand is that the accelerated decay Similar Materials test in Figure 1 provides no data on rate of decay for framing in service:

This test was designed to compare relative performance of materials, so was not a Laboratory Test under clause B2 of the building code, because there is no correlation with service conditions. That is, "proof of performance" does not take into account "relevance to field and service conditions". Rate of decay is only relative to another material, and there is no relationship with what occurs in service (i.e. absolute rate of decay). Indeed, the researcher who undertook the test above, Mick Hedley, stated that "while relative rates of decay in laboratory tests are reasonably easy to determine, absolute times under real-life conditions are considerably more difficult" (Hedley et al. 2010). 

Heartwood for larch, lusitanica cypress, macrocarpa and Lawson cypress are all naturally durable acceptable solutions for use as framing under NZS 3602:2003 Timber and Wood-based Products for Use in Building. They were included in the standard by virtue of their long History of Use as framing and well proven service performance without failure under framing exposure conditions. These are all therefore reference materials suitable for Similar Materials testing under clause B2/VM1 of the building code. Based on the results above (Figure 1) the relative performance of Douglas fir is slightly lower than for larch, so would fail the Similar Materials test with larch as the reference material.

What is also clear above is that the relative performance of radiata heartwood was very poor compared with larch heartwood. Consistently over the duration of the test, larch heartwood took four times longer to reach the level of decay attained by radiata heartwood. This framing test verified the poor performance from radiata heartwood relative to other species, vindicating its earlier removal from NZS 3602 in 2003 based on catastrophic failures in service, while larch was retained. To reiterate, this test (Figure 1) compared the relative durabilities of these "similar materials" and did not consider in-service (absolute) durability performance.

Only the Laboratory Test method can pass or fail a material based on absolute performance criteria (such as length of time and residual condition). Under building code clause B2/VM1, the Laboratory Test can verify durability performance by assessing the relevance of the test to field and service conditions. Laboratory tests would therefore need to correlate test decay with in-service decay, but this requires a performance threshold. Unfortunately, no performance threshold exists (e.g. "duration of wetness") in clause B2 of the building code for enclosed timber framing that gets wet and stays wet. The only benchmark we have is a minimum of 50 years in service for framing.

H1.2 framing and boron treatment

The level of boron (0.4% Boric Acid Equivalent BAE) required for H1.2 framing was set by the regulator in 2003 at double the level required to inhibit decay (Jeanette Drysdale, pers. comm). By default this is acknowledgement that boron treated timber has different degradation mechanisms to naturally durable timber and is therefore not a Similar Material under B2/VM1 Durability Evaluation. Indeed, the level of boron in H1.2 solid timber framing (0.4% BAE) was set without in-service performance data to support the prescribed level of preservative. Instead, sufficient redundancy was built in to ensure the treatment was reliable under service conditions where leaching might occur (the H1.2 hazard class).

Figure 2 shows accelerated relative decay between H1.2 and untreated radiata using the Scion Framing test. The H1.2 boron treated radiata pine had an initial concentration of >0.4% BAE.

Ten years later the H1.2 boron treated timber was in good condition (over 8/10) while the untreated pine had completely decayed in 4 years under the warm, moist test conditions.

What this Scion "framing test" actually shows is that the method does not account for leaching. Indeed, the protocol only requires that samples "shall be periodically sprayed with water to maintain the wood moisture content at a level suitable for decay to progress" (AWPC 2015). Leach rate, although potentially the most important variable influencing rate of decay for boron-treated timber in service, is not controlled for under the Scion framing test. Yet boron preservative is higly mobile and leachable.

Boron will continue to preserve wood until the level is no longer sufficient (below 0.2% BAE). In the above example (Figure 2) decay does not occur for a considerable period of time, suggesting a very low leach rate. That's okay for comparing relative durability of materials that are indeed similar, such as boron treated poplar framing with a boron treated pine framing reference. But what about untreated timber?

Natural durability is not leached. In an enclosed framing environment where wood becomes wet and stays wet, naturally durable timber will not be subject to increased degradation while water infiltration continues. Once the wood reaches moisture saturation point, additional moisture has no effect on rate of decay. In contrast, boron will continue to leach with additional infiltration of water and the faster you leach boron from treated timber, the sooner it will decay. Leach rate would confound tests that attempt to compare boron-treated H1.2 framing timber with naturally durable timber. These are not Similar Materials because under B2 the materials have different "degradation mechanisms". 

Development of Laboratory Tests

The Scion Framing test, as a similar materials test, cannot be used for removing an existing acceptable solution from NZS 3602, because the listed species are the reference materials. These species therefore provide the Similar Materials test performance benchmark. In the absence of evidence clearly demonstrating premature decay in service, the only method available for determining suitability of current acceptable solutions for framing (cypress and larch heartwood) is the Laboratory Test.

For a Laboratory Test to be devised for enclosed framing, leach rate of boron (as a "degradation mechanism") would need to be quantified for field and service conditions so that H1.2 timber can be tested.

There are two important conditions that can induce leaching of boron from framing timber in service:

1. Leaching under construction (exposed to weather). This has been studied and is fairly slow because timber dries out between wetting (rainfall) events.
2. Leaching in service (leaks in the building). This has not been studied, but once enclosed framing becomes wet, it tends to stay wet. Wood that becomes wet and stays wet leaches readily - all that is required is a source of more water (such as a leak).

Yet surprisingly, I'm not aware of any in-service research undertaken by Scion to date to study durability performance of H1.2 boron-treated enclosed framing under different leach rates, despite water infiltration being the most important degradation mechanism. Indeed, laboratory test performance comparisons are neither practical nor possible until a "reasonable" in-service leach rate is settled on for a leak into enclosed framing. Research that quantifies in-service leach rates for enclosed framing according to rainfall and leak type is a crucial prerequisite for developing the laboratory test.

There are two other prerequisites for development of Laboratory Tests:

1. Correlation of service decay with accelerated Test decay rate;
2. Lastly and most importantly, Laboratory Test methods cannot be developed in the absence of a durability threshold for timber framing in service. Such a pass/fail threshold would require a duration of wetness (length of time) and the acceptable condition (a quantity) for the framing after that length of time. These would need to be defined by the regulator for timber framing. Duration of wetness is the time period it should reasonably take to find and remedy a leak. A line in the sand is required, one that deems that a leak can be remedied before the framing decays. This "durability threshold" would need to be set by the regulator before Laboratory Tests could be developed.

Conclusions

So do Laboratory Tests need to be developed? Growers need to be able to verify their species as having a proven level of durability for use as enclosed framing, a level that meets the requirements of New Zealand's performance-based building code. This can be achieved via Similar Materials tests. However, similar materials tests cannot be used for removing species that are already acceptable solutions, because reference materials cannot fail the test, they are the benchmark for the test.

So what is an acceptable level of durability for timber framing? Only the regulator can make that call. This puts the grower in a vulnerable position where the regulator might "change the rules" and shift the benchmark. I would suggest that test methods must be objective, equitable and stand the test of time. Growers deserve no less because it takes decades to grow trees and the investment in those trees is significant.

References

AWPC (2015) Protocols for assessment of wood preservatives. September 2015 Revision. Australasian Wood Preservation Committee.

Hedley, M. Page, D. van der Waals, J. (2009) A comparison of rates of decay and loss in stiffness of radiata pine and Douglas fir framing lumber. Scion.

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. Scion.

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.

---

Building System Legislative Reform Programme, public consultation

Dean Satchell's blog
Tuesday, April 23, 2019

So how might this affect growers and producers of specialty timbers? Well, I have concerns around product assurance and in particular product certification for building products.

CodeMark certified products are deemed to comply with the Building Code. Importantly, CodeMark is an unchallengeable form of product assurance that has legal status equivalent to an Acceptable Solution.

To put this into context, under the building code, before a new product can be used in buildings, evidence is required proving that durability exceeds a minimum performance threshold (as years in service).

Evaluating products for CodeMark certification is undertaken by the Certification Body, who produce an Evaluation Report that is supposed to consider code compliance. However, although this report forms the basis for the decision to award a CodeMark certificate, the basis for approval is not provided within the certificate itself. Indeed, the Evaluation Report is kept by the certifier and not made available for review, so product assurance is deemed to be provided only by the Certificate of Conformance.

So is this adequate? Is the certificate alone a satisfactory means of assurance for code compliance of the product in question? Definitely not, in my view this amounts to certifier self regulation because certifiers aren't accountable for their decisions made behind closed doors. The certificate just says the product has the tick of approval, but provides no basis for that.

Certification bodies compete in the market for business, and applicants want the competitive edge. Keep in mind that the whole purpose of the CodeMark Scheme is to provide confidence to building consent authorities and assurance to the market that certified products conform to the requirements of the building code. In light of accreditation being recently revoked for one of the product certification bodies (BCS), and given that MBIE has started a review of all BCS-issued certificates (and have even acknowledged that certification needs strengthening), one might ask whether the system is open for gaming and whether the consumer has been adequately protected to date by the CodeMark scheme. Our building code is performance-based, after all, so a lot is at stake.

So is the credibility of CodeMark certification really in question? Lets have a look at some examples of certified cladding, in particular CodeMarks that have been issued to Abodo and Hermpac for their certified exterior cladding timber products and systems.

Weatherboards

Under NZS 3602 (the Acceptable Solution for durability), weatherboards made from cypress, redwood and cedar can all be stained, oiled or left natural. Larch, because it is less durable, requires paint protection to meet the minimum 15 year durability performance requirement. Those are the rules.

Therefore, under New Zealand's performance-based building code, to certify a larch cladding product without paint protection (i.e. just an oil coat), proof (i.e. strong evidence) would be required that the product exceeds the minimum durability requirement of 15 years service. Although such evidence may not be easy to produce for a new product or species, those are the rules and adherence to them would form the basis for any valid decision on compliance.

Hermpac

Hermpac, a timber importer, have included Uncoated or Oil coated Siberian larch Larix siberica as their product "DuraLarch" in two out of three of their CodeMark certified cladding systems.

So what is the durability of this new product, given that it is outside the scope of the Acceptable Solution, NZS 3602? Unfortunately I can't answer that because the basis for the decision is not available to me. I cannot review the evidence, all I have for assurance are the certificates of conformance.

Hermpac hold three CodeMark certificates of conformity for weatherboard products, all issued 31/3/2017:

• Hermpac VertiLine Vertical Shiplap Weatherboard Cavity System;(CM30036) and
• Hermpac Rusticated, Splaycut and Multi-Splay Weatherboard Cavity System. (CM30037) and
• Hermpac Bevelback Weatherboard Cavity System;(CM30038)

In all three certificates the Australian-based certifier Global-Mark states that to meet the requirements of Clause B2 of the building code they have "relied on the independent expert and/or laboratory advise or reports" in evaluating the product. That reads a bit like smoke and mirrors, but appears to me to be stating that expert opinion can be relied on as proof of durability for the product. In reality Clause B2 spells out that the evidence required is History of use, Similar materials tests and/or Laboratory tests. Expert opinions can only support the evidence.

Now, if a product does not comply with the Acceptable Solution (in this case NZS 3602:2003), under the CodeMark scheme rules the Certification Body shall "ensure that the evaluation methodology and evaluation plan includes an Alternative Solution that has been prepared in compliance with the requirements of the NZ Building Code and which clearly demonstrates how such requirements have been satisfied" (See 2.2 Evaluation methodology). But how can I be assured that this has taken place if I can't review that Alternative Solution? All three of Hermpac's CodeMark conformity certificates list "DuraLarch" (Siberian larch, Larix siberica) but even though it was mandatory that an Alternative Solution be prepared, all I can do is trust that this was prepared. Allowing product certificates to have such content deficiency is clearly inadequate, given that product certification must be accepted by every Building Consent Authority as complying with the Building Code.

Digging a bit deeper, actually the Building (Product Certification) Regulations 2008 requires "a reference to the existence of any information that forms part of the certificate or the basis for certification". But in the Hermpac certificates there doesn't appear to be any reference to the existence of an Alternative Solution. So do their certificates even comply with the regulations?

There are also key differences between the three certificates that suggest things are awry.

In Hermpac's Bevelback Weatherboard Cavity System the certificate states that:

"Cedar weatherboards are finished with two coats of premium penetrating oil stain to Herman Pacific Limited specifications while Dura-Larch and Ashin-Dura weatherboards are treated to H3.1 and require a primer coat and two coats of exterior grade acrylic latex paint"

This contrasts with Hermpac's Rusticated, Splaycut and Multi-Splay Weatherboard Cavity System and VertiLine Vertical Shiplap Weatherboard Cavity System certificates, which only state that:

"Cedar and Dura-Larch weatherboards are supplied either raw, with one coat of machine applied premium penetrating exterior grade oil stain to Hermpac specifications"

So what is so different about the Dura-Larch in these products such that Siberian larch timber requires both treatment and paint protection in the bevelback product? Or is this just careless certification, that regardless of contradictions and inconsistencies, has become enshrined as unchallengeable?

Such inconsistencies don't end there. Only the Bevelback Weatherboard CodeMark certificate defines what Dura-Larch is (Siberian larch heartwood), so the other two CodeMark certificates name proprietary timber products without even stating what species they are. In my mind this introduces anti-competitive practices into the CodeMark scheme, setting a precedent that I am not comfortable with. Timber species can't themselves be proprietary branded products.

There are also other issues with the Hermpac CodeMarks. The other species allowed for their three CodeMark weatherboard systems is Western Hemlock, a product Hermpac call "Ashin-Dura". All three CodeMark certificates state that Ashin-Dura must be treated to H3.1. But the timber treatment standard NZS 3640:2003 does not allow Western Hemlock to be treated to H3.1, so it can't be called H3.1. Of course the penetration and retention levels of the chemicals could be defined in an Alternative Solution, but this would require submission of evidence demonstrating durability equivalent to H3.1 radiata weatherboards before this product could go to market. Was evidence supplied with Hermpacs CodeMark applications and was this evaluated by the Certification Body? I don't know because that information isn't available, there is no reference to it in the certificate.

Together, these certificates look to me (on the outside with no way of looking in) like they are riddled with appraisal errors and shortcomings that have graciously provided Hermpac a loophole to supply larch into the natural cladding market.

Hermpacs marketing machine certainly recognises that natural timber cladding is in demand, either uncoated, or only coated with oil or stain. There is definitely commercial advantage in certified products made from timber species that are not currently allowed by the Acceptable Solution, NZS 3602:2003.

Indeed Hermpac have produced a wonderful colour brochure that portrays the warm attributes and good looks of natural timber weatherboards made from their Larix sibirica. Their CodeMarked Larix siberica can be used without paint. Or perhaps only DuraLarch, not actually the species itself? Hang on, the page says species information. I wonder what a Building Consent Authority (BCA) would do when presented with an oil coated Siberian larch clad house with a drained cavity, if that larch was supplied from a third party? Would the BCA accept this species without question because Hermpac have been selling it for years?

Digging a bit deeper, there might be an explanation for the shortcomings in Hermpacs three CodeMark certificates. It appears that Hermpac's CodeMark certificates are copied from BRANZ appraisals that date back to 2014 (before the CodeMark scheme and rules were put together):

• Hermpac VertiLine Vertical Shiplap Weatherboard Cavity System.(Appraisal 650, 2014)
• Hermpac Rusticated, Splaycut and Multi-Splay Weatherboard Cavity System (Appraisal 658, 2014)
• Hermpac Bevelback and Rebated Bevelback Weatherboard Cavity System (Appraisal 663, 2014)
• Hermpac Board and Batten Weatherboard Cavity System (Appraisal 828, 2015)

In these four appraisals the products are all cavity-based timber weatherboard external wall cladding systems for buildings. The products are all to be finished with a penetrating oil stain or an exterior paint system. The Hermpac Weatherboards themselves are manufactured from Canadian Coastal Western Red Cedar, DuraLarch (Siberian larch heartwood) and Ashin-Dura (Western Hemlock). The Cedar and DuraLarch weatherboards can be "supplied unfinished for site finishing with stain or paint prior to installation", whereas Ashin-Dura weatherboards "are treated to Hazard Class H3.1 and must be paint finished only".

What these appraisals all say is that "in the opinion of BRANZ, the Hermpac (all four appraisals) Weatherboard Cavity System, if designed, used, installed and maintained in accordance with the statements and conditions of this Appraisal, will meet the following provisions of the NZBC: Clause B2 Durability". These appraisals do not reference any Verification Methods used to prove durability of Siberian larch with a stain coating for timber weatherboard external wall cladding. I'm puzzled by this and actually wonder if BRANZ were even aware that larch is not an Acceptable Solution for stain-finished weatherboards. If so, they might not have realised that proof of durability performance was required. Or did they verify durability performance but just didn't publish the proof or any reference to it? There is no reference in any of the BRANZ Hermpac appraisals to such information, yet this is required by the regulation because it would form the basis for certification. Noting that product certification must comply with the building code, was it only BRANZ's opinion on which Global-Mark based their decision to CodeMark certify the three weatherboard systems that use oil-coated larch? If there were an adequate audit process, this information would be available in the Evaluation Report for review.

So was the CodeMark Certification Body on the ball, or were they just rubber stamping the previous work by BRANZ without considering code compliance? That wouldn't be a good look. But I don't know because although the evidence might actually exist, the certificate has no reference to it. I can't review the appraisal nor the evidence. This needs fixing.

Abodo

Abodo hold CodeMark certification for two untreated timber cladding products:

• Abodo's Tundra product, made from Douglas fir heartwood
• Abodo's Vulcan product, made from thermally-modified pine

Douglas fir heartwood is of lower durability than larch so is not allowed for cladding under NZS 3602. The Alternative Solution would therefore need to prove that Douglas fir heartwood is of sufficient durability for weatherboards, even if paint-protected.

Abodo actually have a CodeMark certificate for their Weatherboard Cladding product that doesn't even list species. The document doesn't list much at all but does reference Abodo's manual dated Jun 2016. Their manual states that coating is to be done according to coating manufacturer's instructions but doesn't state that paint coating or priming of their CodeMark products is mandatory for compliance with the building code.

Instead, equivalence is claimed to an acceptable solution in NZS 3602 that does require paint coating (H3.1). In their manual, Abodo state that their thermally-modified radiata cladding "has been assessed for minimum H3.1 durability and approved as an acceptable alternative to species listed in NZS3602:2003 Table 2A". However, timber treated to H3.1 MUST be coated with primer and then at least one top coat of paint (as per NZS 3602:2003). Therefore the cladding product should either be paint coated or Abodo should claim equivalence to a specific acceptable solution that doesn't require paint protection. So how did Abodo convince the certifier that their glulam thermally-modified weatherboard (Vulcan+) product wouldn't need painting? The evaluation and grounds for compliance are not stated in either the certificate or the manual. The consumer really should know how or if they conformed with the durability performance requirements of the building code to gain their conformance certificate and commercial advantage. Perhaps the vertical grain orientation in their glulam boards enhances durability, but was proof provided that this is indeed the case? If the quality of their product was high enough to sway the opinion of the certifier, according to the CodeMark rules this would then need to be documented. This certainly isn't referenced in the certificate or manual as required by the regulation. The requirement is actual evidence of durability performance.

For their Tundra cladding, Abodo's manual states that Douglas fir heartwood "has been assessed an acceptable alternative to species listed in NZS3602:2003 Table 2A", apparently by Scion. Was this claimed assessment by Scion an expert opinion, or actual proof that Douglas fir heartwood is good for at least 15 years as unpainted cladding?

So can Abodo's Douglas fir heartwood be used as cladding without paint coating? Well, in the Abodo manual there isn't actually a requirement that Douglas fir heartwood be paint protected.

Now, I don't have an issue with Douglas fir being approved for cladding. My issue is that the process for this requires evidence that proves it will last a minimum of 15 years as cladding. Douglas fir heartwood is not a proprietary product so whatever the evidence was that Abodo used to get their product to market, anybody can use. The floodgates are opened and we don't even know what the evidence was.

Conclusion

Certification of products in the absence of adequate scrutiny results in products that fall through the regulatory cracks to give the applicant commercial advantage. None of the CodeMarked products described above reference the basis for code compliance and none of them reference a Verification Method or Alternative Solution. In all cases the appraisal system appears to have failed the consumer, who has a right to know that the product they are buying conforms. The manufacturers claim nothing more than an estimate of serviceable life. But what the consumer and regulator both require is proof that the product performs, a true assurance that the product's durability is code-compliant. Is CodeMark providing that?

My gripe is that I can't review the actual basis for approval for any of these products. I stress that an opinion is not what gets a new product past the conformance mark, this isn't the Wild West. What is required is evidence that proves that durability performance is adequate.

Heres the rub – by giving a proprietary product commercial advantage without disclosing the means for such advantage, either a monopoly is established, or the floodgates are opened for copycat producers. This occurs and nobody even knows why. So will the next person that comes along be treated the same by a Certification Body if the methodology is not disclosed for their previous decision?

The Alternative Solution should be available for review by me, by the applicant's competitors, by BCA's, by the regulator. That is called transparency. Transparency is required for scheme integrity. A line must be drawn in the sand. Even competitors have a right to know what evidence was provided that proved adequate performance of a product. The actual method used to prove durability should not be withheld from competitors, because this would amount to unfair advantage. If the product is approved, the test method must then become the benchmark for me or anybody else who wants to, for example, introduce a new species treated to H3.1 into certification. There must be a level playing field. Sure, the methods used for manufacture of proprietary products can remain confidential, but the test methods used must be transparent and made available for scrutiny. Legitimate decisions on compliance must not be judgment calls made by the Certification Body, but a pass or fail based on code-compliant Verification Methods.

Can the certifiers' decision be called into question? Can we rely on the regulator to review all Evaluation Reports for code compliance? Is it okay to pass conformance evaluation to third parties without any means for independent audit of the decision? How can certifiers be held accountable for their decisions? The answer is that there should be sufficient regulatory and technical oversight, with mandatory audit of the basis for every certifiers decision.

Dean Satchell
Chair, Farm Forestry Timbers Society

---

---

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