Farm Forestry New Zealand

Report: Pathways to Building Code compliance for farm-totara timber

June 2016
Dean Satchell
Sustainable Forest Solutions
dsatch@gmail.com

PDF version of this report »

Totara and the building code

Executive Summary

The path to compliance would ideally be one leading to 'Acceptable Solutions' in terms of the Building Code. This would require research and testing, especially into levels of durability that would first provide suitable evidence to comply under what is termed 'Alternative Solutions', followed by advocating for changes to compliance documents, especially NZS 3602, so farm-totara would comply as Acceptable Solutions.

Products that should be tested for code-compliant durability performance include structural timber, exterior cladding, exterior joinery and decking.  Durability performance of structural elements should be compared to H1.2 treated radiata pine and untreated Douglas fir. Exterior cladding and decking should be both tested in service for evidence of meeting the 15 year durability performance required in NZS 3602, along with accelerated decay testing to compare natural durability of farm-totara with H3.1 radiata for cladding and H3.2 radiata for decking.

Industry collaboration with Scion should continue, including undertaking wet-framing tests, boron impregnation and diffusion tests, and heartwood characterisation. Results of durability performance testing would take some time, but lead to the improved understanding required for code-compliance.

NZS 3602 is expected to be reviewed during 2016 or 2017 and the New Zealand Farm Forestry Association (NZFFA) are expected to have representation on the Standards Committee. The representative could advocate for a revised standard that is more inclusive of farm-totara, especially for non-structural interior finishing timber and flooring. Longer-term, evidence of durability performance could lead to future revisions that include farm-totara as an Acceptable Solution for structural applications, cladding, exterior joinery etc, depending on the outcomes of the testing.

Paths, required tests and actions to achieve compliance of farm-totara timber with the New Zealand Building Code, are set out in the recommendations of this report.

Establishing Building Code compliance for farm-totara timber is likely to have an immediate and significant impact on the market demand and greatly increase the potential value of the resource to land-owners. It is also an essential part of the process to facilitate development of a new forest industry, one based on the sustainable management of totara forests on private land in many regions around New Zealand.

Introduction

Totara is a prominent feature of the rural Northland pastoral landscape, typically regenerating on erosion-prone pastoral hill country and favouring lower-quality pastures. Because it is relatively unpalatable to grazing stock, 'farm-totara' regenerates so prolifically that many pastoral landowners have regarded it as a weed. However, over the last century or more substantial areas of dense second-growth totara-dominated stands have developed with the potential to be managed as a sustainable resource, complementing the existing pastoral farming land use. 

Potential exists to develop a significant regional industry in Northland based on the use of timber from regenerating (and planted) totara on private land – “farm-totara”⁹. Encouraging sustainable management of the resource sustainably would bring multiple benefits to the region and provide a vehicle to realise ecological, environmental, cultural, social and economic benefits. This has been the vision of the Northland Totara Working Group. Since it was formed in 2005, the group has successfully conducted many projects to progress this initiative.

Presently, the primary focus is on developing the opportunity in the Northland region. However, this opportunity could extend to private land, including Maori land, and in many other regions around the New Zealand.

Under the umbrella of Tane’s Tree Trust the NTWG is represented by a wide range of stakeholders in Northland including the New Zealand Landcare Trust, landowners, New Zealand Farm Forestry Association, the District and Regional councils in Northland, wood millers and processors, research providers including Scion, and representatives of the Ministry for Primary Industries.

The major objectives of the NTWG include:

• identifying gaps and supporting research into determining wood properties and potential uses of farm-grown totara;
• investigating the feasibility of developing a supply chain from resource to market; and
• identifying and overcoming impediments to sustainable management of naturally-regenerating and plantation totara.

This project is part of that wider and ongoing initiative.

Totara is an iconic native timber tree species in New Zealand. However, traditional use and knowledge is based on timber from ‘old-growth forests’ (– i.e. trees that were often many hundreds of years old). Timber from regrowth or farm trees, known as 'farm-totara', has been confirmed as a high quality native timber with strong market interest¹¹. Farm-totara has lower levels of heartwood than old-growth totara traditionally harvested in New Zealand and used for applications requiring high levels of durability. Little is currently understood about durability performance of farm-totara for applications that are required to comply with the Building Code such as cladding and structural elements. This uncertainty has been identified as a major impediment for landowners wishing to manage, market and utilise the resource. There are a range of approaches which may achieve code-compliance, including durability and preservative treatment tests that lead to amended compliance documents. However, the steps are to firstly investigate and analyse the current situation, then set out recommendations for practical pathways to achieve optimal Building Code compliance for farm-grown totara timber products that lead to market development opportunities.

Applications requiring Building Code compliance such as cladding, joinery (exterior and interior), flooring and panelling (interior linings) are investigated. Structural applications are also considered. Although structural timber markets tend to generally be low value and commodity-based, there may be high-value opportunities for decorative structural applications that use higher grades of appearance timber, such as in rafters, beams and laminated members.

This has been a grower/industry-led investigation to ensure that future work and efforts are well targeted for maximum benefit and relevance in terms of commercialising farm-totara as a sustainable economic resource. This involves timber from naturally regenerated ‘second-growth’ trees on private land¹⁰.  Therefore, recommendations in this report are tailored for relevance to timber from what is being termed the farm-totara resource.

Totara and issues of Building Code compliance

The Building Code contains compulsory rules for all new building work and sets out performance criteria that building work must meet.

The Building Code does not prescribe how work should be done, but states how completed building work and its parts must perform. An advantage of a performance-based Building Code is flexibility - it contains no prescriptive requirements stipulating that certain products or designs must be used. This flexibility offers opportunities for developments and innovation in building design, technology and systems⁸. However, demonstration of adequate performance of building materials in specific applications is required, either by providing evidence of compliance (such as durability performance), or by using Standards that offer code-compliant materials or methods.

Compliance with the Building Code can be demonstrated using various pathways. Some pathways must be accepted by the building consent authority as meeting the performance requirements of the Building Code⁸. Compliance paths such as Acceptable Solutions are desirable because designers are likely to specify materials that comply with Acceptable Solutions. Thus ready markets exist due to the ease with which consent is granted.

Chemical treatment

Options for chemical treatment of farm-totara to Hazard Classes greater than H1.2 (such CCA pressure treatment, LOSP etc.) are not considered in detail in this report, noting that NZS 3640:2003 Chemical Preservation of Round and Sawn Timber specifies that Hazard Classes H2, H3.1, H3.2, H4, H5 and H6 apply only to Pinus species. Heart totara is well known to be resistant to the uptake of CCA treatment, but the sapwood, although moderately resistant can be successfully treated. Anecdotal evidence indicates that LOSP has also been successfully applied with good resulting durability for external applications. Chemical treatment may therefore, provide a ‘fall-back’ contingency option for building code compliance where Hazard Classes greater than 1.2 are required. However, the Industry views such chemical treatment as a highly undesirable pathway, one that would likely create a disincentive for the use of farm-totara timber. Boron treatment, however, has been investigated and is discussed within this report.

Compliance with the Building Code, for specific uses, based on the natural characteristics and constraints (particularly durability) of the farm-totara timber resource has been the focus of this investigation.

Structural durability

Timber, being a natural material, is variable in durability performance depending on species, application and conditions it is exposed to in service.

"Leaky buildings"

Leaky buildings are described as those that both allow water to penetrate the building envelope or cladding system and that then hold the water in the wall cavity, where it may remain for some time. This results in the building's timber framing staying wet, raising its moisture content to levels that then allow fungal growth. It should be stressed that although the Building Code requires framing timber to be durable for 50 years, any timber, regardless of the standard to which it is treated (including the H3 standard) will decay if it remains wet (Parliament 2002).

The Building Code

Although the Building Code now requires structural timber to be treated to a minimum of H1.2 boron (0.4% BAE), the exception allows untreated Douglas fir to be used where the building is a traditional low risk house (Clause 3.2.2.2 B2/AS1). Justification for this exception was based on research showing that untreated douglas fir sapwood was more durable than radiata pine sapwood.

The required level of durability (in years) under situations of moisture ingress does not appear to have ever been defined for such low risk houses, and thus the only option available is an Alternative Solution that involves comparing and testing levels of durability for farm totara against Douglas fir.

Research Results

Research undertaken by Scion on decay resistance of framing in situations where moisture content is raised, showed that sapwood of cypress species had higher durability than sapwood of Douglas fir¹. Larch sapwood was of equivalent durability to Douglas fir sapwood and heartwood of both larch and Douglas fir was also of equivalent durability. However, NZS 3602 Timber and wood based products for buildings, has not been updated to reflect the results of this research, nor has Clause B2/AS1 of the Building Code. Farm-totara was not tested.

To meet the durability performance requirements of the Building Code, testing would at least need to demonstrate equivalent or better durability than untreated Douglas fir. If totara sapwood were tested to have equivalent or better durability than Douglas fir sapwood, then either NZS 3602 or B2/AS1 3.2.2.2 could be updated to include totara as complying with the durability requirements of the Building Code as an acceptable solution for structural timber not requiring treatment in houses of low risk design. If farm-totara were shown to have equivalent durability to H1.2 treated radiata pine, NZS 3602 could also be updated to allow farm-totara to be used as an acceptable solution in all applications requiring H1.2 treated radiata, as complying with the durability performance requirements of the Building Code.

However, at present, the appearance characteristics of farm-totara timber in respect to differentiating sapwood from heartwood and the possible existence of a transitional zone of ‘intermediate wood’, are not well understood nor yet quantified in terms of natural durability. This also needs to occur in order to confirm that visual grading is possible for building-code compliance under some applications.

As an interim measure prior to inclusion in NZS 3602, testing of durability performance as framing with raised moisture content would offer evidence suitable for alternative solutions. Although building consent authorities allow alternative solutions at their discretion, compelling evidence of equivalent durability to either untreated Douglas fir or H1.2 treated radiata would allow the important first steps in market development to take place, with industry-supported education (e.g. via the Northland Totara Working Group or Farm Forestry Timbers) leading to acceptance as a building material the likely outcome.

Compliance paths

The following flow chart outlines the compliance paths for timber under the Building Code. Totara complies with B1 (Structure) because characteristic stresses have been determined for the species. However, because totara is not listed in NZS 3602, the only compliance path currently available for B2 (Durability) is via an Alternative Solution.

The flow diagram above illustrates that each building consent authority would need to be satisfied that farm-totara complies with the Building Code as an alternative solution under Clause B2 Durability. For a generic alternative solution to be prepared for structural applications using farm-totara, technical information would be required demonstrating compliance.

Verification Methods for durability

The durability clause (B2) in the NZ Building Code contains specific default minimum service lives for buildings and their components. Structural elements, including structural fixings and bracing materials, have a 50-year service life requirement.

The minimum requirement for a H1.2 treatment for timber framing is to provide protection in-service. However, H1.2 preservative treatment is not designed for extended exposure to elevated moisture content³.

NZBC B2 VM1 provides some guidance for proving durability performance, but this is limited in scope. For example there is no Verification Method for proving durability performance of structural timber, because the expected in-service exposure conditions, if taking into account the possibility of moisture ingress and entrapment, would not meet the expected service life of 50 years under the H1.2 Hazard Class. Test methods or in-service history would require a defined threshold of time to decay where exposed to moisture content conducive to decay. Such test methods should be standardised for both treated and untreated timber.

A Verification Method for durability performance based on time to decay would provide a "level playing field" for testing chemical treatment, modification methods and natural durability (for example structural elements potentially subject to moisture entrapment) against a benchmark durability threshold as time before decay.

Acceptable Solutions for durability

NZS 3640:2003 Chemical preservation of round and sawn timber sets out requirements for the preservative treatment and identification of timber to provide protection from decay and insect attack, based on six hazard classes that are described in the Standard.

NZS 3640 clause 1.2 states that:

The requirements for hazard class H1.1 and H1.2 apply to all species for which hazard class H1.1 and H1.2 is specified in NZS 3602. Hazard classes H2, H3.1, H3.2, H4, H5 and H6 apply only to Pinus species⁴.

While it may be possible to treat other species using the provisions of this Standard, such treatments are outside the scope of this Standard and the adequacy of the resulting treatments will need to be demonstrated⁵.

It is not clear how building consent authorities would view "demonstration" of "adequacy" to remain an Acceptable Solution, or whether they would view such demonstration as an Alternative solution.

NZS 3602 does not include totara as an Acceptable Solution for any application, including structural, cladding, decking and door/window joinery. Review of standards offers an opportunity to provide evidence supporting inclusion.

It should be noted that for structural applications, sapwood of all species included in NZS 3602 must be treated to H1.2. Natural durability is not yet well understood for farm-totara in different applications, especially the impact radial position of wood in the log has on natural durability.

Importation of illegal and unsustainably produced timber

Trade in illegally produced imported wood products challenges markets for high integrity locally produced wood products such as farm-totara, harvested under Sustainable Forest Management Permits and Plans.

Laws are not currently in place in New Zealand that ensure illegally harvested wood products cannot be imported and sold here. Australia does have such a law in place, the Australian Illegal Logging Prohibition Act. If New Zealand were to follow suit, locally produced legal product would be able to compete on an even footing.

Furthermore, because of the high costs of compliance associated with harvesting regenerated farm-totara, the sawn product would unlikely compete with imported product that has not been managed sustainably. This is because of the low production costs associated with environmentally unsustainable production. A level playing field would offer opportunities for local producers to compete with imported timber.

Such barriers to developing markets for NZ grown specialty timber are not easily overcome, but bodies such as the NZ Farm Forestry Association and New Zealand Wood could apply and maintain pressure on the NZ Government to make suitable regulatory changes that remove the current disadvantages local producers experience.

See the 2010 New Zealand policy to address illegal logging and associated trade here >>.

Fire regulations

Changes made in 2012 to the Building Code provisions for fire safety resulted in a MBIE review initiated in 2014 and a plan to improve fire safety in New Zealand⁶. The resulting Fire Programme was made up of 14 projects, including assessment of timber linings in buildings.

Under the current Building Code provisions, wood products are allowed to be used without restriction as⁷:

• wall or ceiling linings in detached homes or within individual apartment units
• timber joinery, or general decorative trim
• structural timber elements (beams, columns or walls) except that individual structural shear walls may not be more than 3.0 m long.

Note: Small non-conforming areas of up to 5.0 m² are permitted

Commercial buildings such as offices, factories, shops, schools, restaurants etc have restrictions on the use of timber.

As a general rule, walls and ceilings in buildings such as offices and small factories (other than crowd or sleeping occupancies) can use most uncoated, paint-coated or clear coated timber with no need for testing, provided that the wood is⁷:

• at least 9mm thick
• at least 400kg/m³ density for solid wood.

Note: there are restrictions on coating types and density⁷.

Because farm-totara has a market niche as an appearance grade timber, market limitations currently exist for use as appearance linings in some commercial buildings. Such limitations are not likely to excessively constrain market development initiatives for the timber, however.

Conclusions

Studies confirm farm-totara to be a high-quality native timber with strong market interest. However, at present, uncertainty around building code compliance, particularly relating to durability performance, is a major impediment to the commercial use of farm-totara timber. This severely limits the potential markets and value of the timber. Establishing Building Code compliance is likely to have an immediate and significant impact on market demand and greatly increase the potential value of the resource to land-owners.

Barriers to compliance could be overcome by targeting research to prioritise achieving code-compliance for products with greatest market potential, and according to a plan that carefully considers costs, time-frames, pathways, decisions, outcomes and consequences as a decision tree.

Because there is currently a limited knowledge-base on timber properties that influence selection of marketable products, considering market potential for products is interdependent on determining code-compliance. Therefore, some assumptions would be required in prioritising research and testing. For example testing of durability performance is a clear priority, but this needs to be considered in relation to products and timber properties. Timber properties that affect natural durability or impregnation with chemicals, or processing/drying issues all contribute to decisions on product mix options.

It is suggested that two visual grades, based on timber colour, should be tested for durability in all applications, these being “heartwood + intermediate wood” and “intermediate wood + sapwood”. Until more is understood about relative durability according to tree age and radial position in tree, such differentiation, although presumptive, is based on industry discussions on likelihood of significant differences in durability performance that would lead to commercial products suitable for purpose.

Durability performance testing

The clear priority is to test relative durability performance of sapwood, intermediate wood and heartwood. Options include accelerated decay methods that compare the resulting levels of durability with Hazard Class preservative treated radiata pine. The relationship between colour of farm-totara timber and durability would need to be tested concurrently. Accelerated decay methods could be used to compare different identifiable colour-based grades with H3.2 treated radiata pine (for assessing compliance as decking applications) and H3.1 radiata (for assessing compliance as cladding applications).

For structural applications the Scion wet-framing test would provide comparative performance levels with H1.2 radiata and untreated Douglas fir. The results would give alternative paths to compliance. If farm-totara were demonstrated to be more durable than untreated Douglas fir and less durable than H1.2 radiata, then untreated farm-totara would be limited to buildings of simple design in the same manner as untreated Douglas fir is. Testing should give consideration to possible differences in durability performance between “heartwood + intermediate” and “sapwood + intermediate” based on visual differentiation of timber colour.

Submissions to MBIE to provide a Verification Method for testing durability performance for structural timber should be pusued by industry so that it is clear what the requirements are in terms of testing methods for structural applications. 

Preservative treatment options for farm-totara also need to be considered, either concurrent with or after the wet-framing test trials. Boron treatment options should be pursued, especially traditional diffusion methods because slow air-drying is standard practice for farm-totara, which may facilitate cost-effective boron diffusion treatment methods. Diffusion methodology would need to be tuned to consistently achieve the requirements of NZS 3640 before pursuing this path to compliance. Industry would need to be aware that verification of treatment levels would be required on a producer-by-producer basis. 

If compliance were determined by tests on farm-totara products, documents could be prepared for industry and the market on how to prepare Alternative Solutions. These documents would also form the basis of preparing a case for inclusion in the next revision of NZS 3602, for farm-totara timber to become an Acceptable Solution for the specified application.

Submissions should be made to include farm-totara for interior finishing applications in the next revision of NZS 3602 based on well documented experience and examples showing that the timber is durable for more than 5 years in service.

Flowchart on compliance paths, assuming two timber grades based on visual differentiation of wood colour

Recommendations

This review of the issues and barriers that constrain market development for farm-totara timber products under the New Zealand Building Code is aimed at identifying pathways to code-compliance. The following recommendations are provided in order to develop and implement an optimal and practical pathway for acceptance of farm-totara within the Building Code.

These recommendations focus on the research required to fill knowledge gaps regarding wood properties of farm-grown totara timber and the performance issues that need to be understood to achieve compliance with the Building Code.

1. Submissions for farm-totara to be included in NZS 3602 for interior flooring,  non-load-bearing interior wall framing and stair treads, risers and handrails where protected from the weather and dampness.
2. Explore opportunities for use of farm-totara as a decorative interior face in cross laminated panels.
3. Characterise and describe the wood properties of farm-totara timber, particularly the relationships between apparent colouration of the timber and natural durability levels of sapwood, intermediate wood and heartwood. This needs to form the basis of trials where durability performance is being tested.
4. Undertake accelerated decay ‘wet-frame test’ trials, to compare durability performance of structural timber where subject to moisture ingress, between farm-totara timber and:
   a) H1.2 Pinus radiata and
   b) Untreated Douglas fir.
5. Trial use of sapwood farm-totara timber as exterior window joinery and test coatings as a method of achieving 15 years + durability performance in this application.
6. Trial thermal modification of farm-totara timber and:
   a) compare its durability performance with radiata pine under the same modification process and with radiata H3.2
   b) test strength performance compared with imported cedar as exterior joinery
   c) Set out any conclusions regarding suitable end uses/markets for thermally modified farm-totara based on those test results.
7. Trial durability performance of farm-totara sapwood as external cladding and test coatings as a method of achieving 15 years + durability performance in this application.
8. Trial durability performance of farm-totara in-service as external decking to test achieving 15 years + durability performance in this application and compare with CCA radiata H3.2.
9. Publish the test results, so these are available for use in Alternative Solutions.
10. Advocate for the appropriate amendments to be made to NZS 3602, to be fully inclusive of farm-totara as an Acceptable Solution for end-uses, according to the results of the above trials and tests, to be inclusive of farm-totara as an Acceptable Solution for end-uses shown as appropriate from the results of these trials.

 

References

1. Summary of Tests on Untreated Douglas-fir, Treated and Untreated Radiata pine for Use as Framing in Domestic Construction in New Zealand. Future Forests Research New Zealand, report No. FFR-DS029
2. NZ Building Code clause B2 Durability
3. New Zealand Building Code Clause B2 3.1.1
4. NZS 3640:2003 clause 1.1.2
5. NZS 3640:2003 clause C1.1.2
6. Fire Programme, Ministry for Business and Innovation
7. Use of timber under NZ Building code fire regulations, A. Buchanan & J. Parker, 2014
8. New Zealand Building Code Handbook (2014)
9. Tai Tokerau Northland Growth Study. Opportunities Report February 2015.
10. Bergin, D.O. 2003: Totara establishment, growth and management. New Zealand Indigenous Tree Bulletin No. 1. New Zealand Forest Research Institute. 40p.
11. Quinlan, P. 2011: Existing uses and market development opportunities for naturally regeneration totara timber. SFF Project L10/145. Report for the Northland Totara Working Group. 98p.