Preservative treatment provides wood with added durability. However, it’s a mistake to assume that all pressure treated wood is the same. Whilst one piece of treated wood may look very much like any other, the level of preservative protection could be very different. That’s because national technical standards for wood preservation require that the loading and penetration of preservative, impregnated into the wood, is tailored to the desired end use.

The WPA Code of Practice for Industrial Wood Preservation (January 2021) groups the applications for treated wood into Use Classes, the main three being:

Interior: Use class 2

Exterior: Use class 3(u) and Use class 4

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• Use Class 2
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