Farm Forestry New ZealandThe decay resistance of alternative species in an accelerated framing test Assessment of decay after one year’s exposure
By Ian Simpson and Tripti Singh, March 2023.
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Executive summary
Sets of framing samples were exposed in high humidity conditions of 85-90% relative humidity and 25 – 27°C. The species and preservative treatments included in this test were:
- Eucalyptus fastigata, mixed heartwood\sapwood, untreated and boron treated.
- Eucalyptus fastigata, LVL, untreated and boron treated.
- Eucalyptus nitens, untreated and boron treated.
- Eucalyptus regnans, heartwood, untreated
- Cupressus macrocarpa, young and old trees, heartwood, untreated.
- Cupressus x ovensii, heartwood, untreated.
- Larch, heartwood, untreated.
- Douglas fir, mixed heartwood\sapwood, untreated.
- Radiata pine, mixed heartwood\sapwood, untreated and H1.2 boron treated.
All of the framing samples were periodically sprayed with water at approximately two weekly intervals to maintain the wood moisture content at a level suitable for decay to progress. Before exposure in the high humidity condition, samples were also soaked in water for two hours.
The method of testing followed the procedure described in Australasian protocols in this case for the Hazard class H1.2. This test method simulates the common framing joint in house framing between studs and plates, where in a leaky building, moisture may become trapped and provide suitable conditions for fungi to establish.
After one year’s exposure in accelerated decay conditions:
- Lightly established decay had developed in untreated Eucalyptus fastigata mixed heartwood\sapwood solid wood, untreated Eucalyptus regnans heartwood, untreated Douglas fir mixed heartwood\sapwood and untreated radiata pine mixed heartwood\sapwood.
- The first stages of decay had developed in untreated Eucalyptus fastigata LVL, untreated Eucalyptus nitens, untreated Cupressus macrocarpa from young and old trees, and untreated Cupressus x ovensii.
- There was no decay observed in any of the boron treated samples. This includes boron treatment of solid wood of Eucalyptus fastigata and radiata pine along with laminated E. nitens and Eucalyptus fastigata LVL.
It is recommended that this test is continued and assessed after two year’s exposure in accelerated decay conditions.
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