Treatment Use Class

The eventual end use of preservative treated timber is classified into one of the five main categories shown in the table below. These Use Classes, defined in BS EN 335-1, are based on the potential threat to the timber from decay or insect attack in its eventual application.
For instance, internal building timbers in Classes 1 and 2 will be under less threat than timbers used externally in ground contact - Use Class 4. Therefore, Use Class 4 timbers will require a higher degree of protection.

  • UC 1 - Internal, dry (eg. Upper floor joists)
  • UC 2 - Internal, risk of wetting (eg. Tile battens)
  • UC 3 coated (3.1) - Outdoors, coated, above ground (eg. Soffits/Cladding)
  • UC 3 uncoated (3.2) - Outdoors, uncoated, above ground (eg. Cladding/Fence rails)
  • UC 4 - Direct soil or fresh water contact (eg. Fence posts)

The illustration below shows the typical applications for treated timber 

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