The potential for using heat treatment to improve the properties of North American fenestration species was evaluated on ponderosa pine (Pinus ponderosa L) and yellow poplar (Liriodendron tulipifera L) treated using the ThermoWood process at various treatment temperatures and times. Soil block tests using Gloeophyllum trabeum, Postia placenta, or Trametes versicolor showed that durability was enhanced, but the wood still experienced decay levels that would be unacceptable in window applications. Heat treatment also reduced hygroscopicity, but did not produce a sufficient reduction in moisture uptake to be considered effective in the current U.S. window standards. Heat treatment had no significant effect on flexural properties, but did reduce the ability of the wood to resist impact loads. The results suggest that the heat treatment conditions evaluated were not suitable for improving the durability of either ponderosa pine or yellow poplar to the extent required for fenestration applications.

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