Report: Pathways to Building Code compliance for farm-totara timber
Sustainable Forest Solutions
Potential end uses of totara timber
The author wishes to acknowledge the support from the organisations and individuals that have enabled this project to be undertaken. These include; the Ministry for Primary Industries (through the Sustainable Farming Fund), Tane’s Tree Trust and the New Zealand Farm-Forestry Association, (including the Indigenous Forestry Section), the Northland Totara Working Group members Paul Quinlan and David Bergin for assistance in finalising this report, Michael Hayes & Geoff Cookson, for their time and donated sample boards of timber for testing, and saw-miller, Shane Hyde, for his time and the use of his band-saw in re-sizing some of the timber samples. The time and input from Robin Curtis, CEO of NZ Sustainable Forest Products, is also acknowledged and much appreciated.
In producing this report, reasonable care has been taken regarding the accuracy of the information presented. However, no guarantee as to the truth, accuracy or validity of any of the comments, implications, recommendations, findings or conclusions are made by the author, the Northland Totara Working Group, Tane’s Tree Trust, or any other party. Therefore, neither the authors, nor any of the supporting organisations, shall not be liable for, or accept any responsibility for, any loss, damage or liability incurred as a result of direct or indirect result of any reliance by any person upon information or opinions or recommendations expressed in this work. Users of any of this information, whether contained or inferred, in or arising from this report do so at their own risk.
The New Zealand Building Code provides challenges for those applications where timber is required to comply with durability or structural requirements. Such applications include cladding, decking and structural. For markets to develop with sufficient volumes that support an industry, farm-totara would need to overcome compliance issues for structural applications. There are clear market opportunites for higher grades as appearance exposed structural elements and for lower grades as structural lumber, provided appropriate testing is undertaken that provides Building Consent Authorities and consumers assurance of suitability for purpose.
Cross Laminated Timber (CLT), sometimes referred to as crosslam, is a relatively recent engineered product introduction into the New Zealand market. Panels are produced from sawn timber boards glued in layers. Construction using CLT needs to meet the structural requirements of the Building Code, and thus a 50 year life. Durability performance under clause B2 of the Building Code requires a minimum of H1.2 boron treatment. The exception for untreated Douglas fir for use in buildings of low-risk design might offer an opportunity for use of untreated timber CLT but before considering the opportunity for farm-totara, demonstration of untreated Douglas fir in service as CLT should take place and confidence in that product evident.
One manufacturers has identified this opportunity to produce code-compliant untreated CLT from Douglas fir *. For farm-totara to hold this same opportunity evidence is required that durability performance is at least equivalent to Douglas fir. Frame-tests would provide the evidence to support inclusion, which would need to be followed up by representative participation in relevant standards committees seeking a level playing field.
There may be opportunities for use of farm-totara in CLT applications as a decorative interior face in panels.
Laminated Veneer Lumber (LVL) is not produced as a decorative product and farm-totara does not offer improved strength or stiffness over radiata pine*. Therefore, this product is not one recommended for pursuing as a market opportunity for farm-totara.
Opportunities for developing markets for structural solid timber applications abound for farm-totara.
Lower grades of wood (e.g. FFT No. 2 framing grade) are a by-product from selecting more valuable appearance grades and generally require a market for profitable production of higher grades. If H1.2 treatment and structural verification of visual grades were not necessary, producers might be able to market timber at the "farm gate" thus avoiding overheads and potentially producing commercially competitive farm-totara products. The strength properties of farm-totara suggest that verification would not be necessary for FFT visually-graded FFT No. 1 Structural grade SG6 as either an Alternative Solution or for inclusion in NZS3603 and NZS3604 as an Acceptable Solution. Another opportunity for lower grades is to cut short clear lengths and finger-joint these into lengths suitable for appearance glulam.
Appearance structural applications are essentially an untapped market in New Zealand because of building code constraints that limit compliance to Acceptable Solutions. In the case of totara, by not being included in NZS 3602, durability performance is not established for an Acceptable Solution, with the only option an Alternative Solution which is perceived to be costly and inhibitive by specifiers and designers. Suitable applications for farm-totara include solid-timber exposed beams and rafters, along with appearance glulam.
In New Zealand Structural glulam is primarily produced from radiata pine and Douglas fir, because the Building Code offers compliance for these species as Acceptable Solution. Other species can be used by following the Alternative Solution path. However, architects and specifiers may avoid timber species that are perceived to be difficult to achieve compliance, thus Alternative Solution are viewed as a barrier to the market. Because Farm Forestry Timbers have determined the Characteristic Stresses for farm-totara, the primary constraint to its use as glulam is meeting the requirements for Hazard Class H1.2 (0.4% mass/mass boric acid equivalent) by determining appropriate methods for boron infusion into sawn timber.
Pathways to compliance for structural applications
Two pathways offer alternatives for achieving building code compliance:
- For buildings of simple design, producing evidence of similar or greater durability than untreated Douglas fir would be suitable for Alternative Solutions. Untreated farm-totara could be tested as wet framing against Douglas fir by an accredited and appropriate wood testing entity (e.g. Scion). If evidence were produced that farm-totara was of similar or greater durability than Douglas fir under this test, and evidence that insect (borer) attack is not an issue with farm-totara, inclusion in NZS 3602 as an Acceptable solution under the same requirements for untreated Douglas fir could be pursued.
- For standard structural applications evidence of 0.4% mass/mass boric acid equivalent infusion as per NZS 3640 for H1.2 would be required for either an Alternative Solution or inclusion into NZS 3602 as an Acceptable solution.
Traditionally, heart totara from old-growth forests, was a favoured timber for window joinery. Its dimensional stability and Class 1 durability level made it unquestionably suitable for such demanding applications. In respect to the new farm-totara timber resource, there is a lack of quantitative information on its relative durability and performance. Because differentiating and segregating heartwood from intermediate and sapwood may not be practicable in sawn timber, durability performance falls on the lowest denominator (sapwood) and attaining a durability performance of at least 15 years as required by NZS 3602 may not be consistently achievable. Research could explore coatings, treatments or moisture barriers and demonstrate adequate durability performance of farm-totara external joinery. If evidence were produced of adequate durability, this could be used for Alternative solutions and eventually lead to updating NZS 3602 as an Acceptable Solution.
Thermal modification offers both an improvement in durability but also greater dimensional stability. Research into stability of thermally modified farm-totara for window joinery could open market opportunities for higher grades as high-value decorative wooden window and door joinery if superior to thermally modified radiata pine.
External joinery was a traditional use and market for totara timber, until substituted with aluminium. However, now double-glazing and profiling for better water channelling, requires more material bulk than was previously used. The increased material costs may help make a suitable timber option more competitive.
Compliance with the Building Code also requires testing of window and door joinery for the wind zone and labelling according to NZS 4211.
JMF NZ offer solutions for NZS 4211 compliant timber joinery. NZS 4211 deals with weathertightness in wind zones and registered master joiners can become affiliated with JMF to use the available styles of compliant joinery and have access to the specifications. Because the timber species used for testing the JMF styles of joinery was imported cedar, provided the timber used was of similar or greater strength than cedar, compliance with NZS 4211 would not be an issue. Farm-totara timber is denser and stronger than cedar based on characteristic strength tests undertaken by NZFFA.
However, compliance with NZS 3602 (durability) is an issue because only heartwood for redwood, Western red cedar and cypress is listed in NZS 3602 Table 2 (2A.5, 2A.6) as Acceptable Solutions. If farm-totara were to be tested and demonstrated to have 15 years durability performance as exterior joinery an Alternative Solution could be prepared, leading to inclusion within NZS 3602.
Durability performance of at least 15 years is required by the NZ Building Code for exterior cladding. In-service evidence would need to be established demonstrating greater than 15 years durability as cladding for sapwood. Limiting cladding to heartwood is complicated with farm-totara because of issues with differentiation based on colour and the unknown durability levels of any younger 'intermediate' heartwood zone. If evidence of sufficient durability were established, Alternative Solution would offer the only option for utilising farm-totara as cladding, until NZS 3602 Timber and wood-based products for use in building were to be updated to include farm-totara as an Acceptable Solution for cladding.
Durability perfomance of at least 15 years is required by the NZ Building Code for external decking. Evidence of this being achieved by farm-totara would be required to justify inclusion in NZS 3602 Timber and wood-based products for use in building. Farm-totara sapwood is not likely to hold durability sufficient for this application and grading for durability based on more colour does not yet have sufficient evidence of relative durability performance.
Thermal modification might hold some promise of sufficient durability for decking, however research would need to demonstrate both sufficient strength and durability for this application.
The specified durability level requirement in NZS 3602 for interior flooring timber is 50 years. Totara is not included in table 1 1C.3 Interior flooring, suspended ground floors in NZS 3602 Timber and wood-based products for use in building. This appears to be an oversight and advocating for its inclusion in the next revision of NZS 3602 is required. This would then allow farm-totara to be used as flooring under an Acceptable Solution. Until included farm-totara flooring is an Alternative Solution.
Farm-totara timber is not listed in NZS 3602 as an Acceptable Solution for interior finishing timbers. The requirement is for a 5 year durability performance and advocacy should take place to have farm-totara included in Table 3 – Requirements for wood-based building components to achieve a 5-year durability performance.