New QA tool for thermally modified radiata pine using NIR spectroscopy

A fast, non destructive method for verifying timber treatment temperatures—a game changer for NZ building code compliance.

Stacks of planks waiting to be shipped

A new study has demonstrated a fast, non-destructive method to verify the thermal treatment levels of radiata pine—an essential step for ensuring compliance with the New Zealand Building Code. The research, published in the European Journal of Wood and Wood Products, highlights how near-infrared (NIR) spectroscopy can accurately classify timber modified at different temperatures.

This was a combined effort using postdoctoral and summer-project student-researchers, combined with scientists from the Ferrier Research Institute, BRANZ, and SCION to develop this quality-assurance technique.

Context and significance

Radiata pine, used widely in NZ construction, requires thermal treatment to improve durability if we do not rely on heavy-metal preservatives. However, verifying exact treatment temperatures has been challenging—until now. This method offers a reliable way to check compliance independently.

Radiata pine samples

Figure 1. Radiata pine samples—(a) unmodified, (b) treated at 210°C, (c) treated at 220°C, and (d) treated at 230°C.

Research highlights

What was done

Timber samples were treated at 210, 220, and 230°C. Both NIR spectroscopy and traditional colour measurements were compared.

Novelty

The NIR approach achieved 100% correct classification of samples into the three temperature categories—outperforming the visible colour method (95%) and colourimetric data (87%).

Ferrier contribution

Simon Hinkley and Joel Kidgell contributed to the publication, particularly in the areas of analytical data interpretation and statistical analysis.

Impact and applications

This technique provides manufacturers, regulators, and builders with a quick, non-invasive way to verify timber treatment levels. It’s a vital tool for ensuring longevity and compliance of NZ-built wooden structures—supporting high safety and environmental standards.

“NIR spectroscopy can confirm that a piece of wood has been modified correctly, without needing to know its treatment history,” say the authors.

Read the full paper

“A comparison of NIR spectroscopy and colour measurements for the classification of radiata pine timber thermally modified over a narrow temperature range”, European Journal of Wood and Wood Products, 26 May 2025 (Open access)

View the publication.

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