Specialty Timbers New ZealandSearch technical reports
A comparison of rates of decay and loss in stiffness of radiata pine and Douglas fir framing lumber 2009
By Mick Hedley, Dave Page and Jackie van der Waals, Scion Wood Processing, Private Bag 3020, Rotorua, New Zealand, September 2009.
Download Hedley_et_al_2009_Scion.pdf (pdf)
Executive summary
Stiffness loss with time was recorded for preservative-treated and untreated radiata pine and untreated Douglas fir framing size lumber, which had been pre-inoculated with Oligoporus placenta, a brown rot decay fungus isolated from decaying untreated radiata pine framing. Between stiffness measurements, samples were contained in a plastic tank located outside at ambient temperature. Index of Condition (sensu AWPA Standard E7-93) was assessed for all samples at the time stiffness testing was undertaken.
Substantial loss of Index of Condition was recorded for all untreated samples before there was any significant loss in stiffness. Decreasing order of stiffness loss (and weeks to first measurable loss) was: untreated radiata pine sapwood (24), radiata pine heartwood (48), Douglas fir sapwood (65), Douglas fir heartwood (122), treated radiata pine sapwood (>158). The results indicate that for untreated Douglas fir in particular, the presence of observable decay - the main criterion for replacement of framing when a "leaky building" is rehabilitated - may not truly reflect residual stiffness, which would be retained when leaks were rectified and the framing dried.
Key words: radiata pine, Douglas fir, framing lumber, decay, stiffness
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