Preservative treatment protects timber from moisture, decay and biological attack. But it’s important to understand that treated timber is not a uniform standard – the level of protection offered depends on how the timber is treated and how it will be used.
RESOURCES
Understanding timber treatment
Why treatment matters
A quick guide to treatment user classes
UK standards for wood preservation require that treatment is matched to the environment the timber is exposed to – if it isn’t, the timber can fail prematurely. That’s why treatment standards based on clearly defined usage conditions, or ‘Use Classes’.
| USE CLASS | ENVIRONMENT | TYPICAL APPLICATIONS | EXPOSURE LEVEL |
| UC2 | Interior, protected from weather | Roof timbers, internal framing, floor joists | Low risk (occasionally damp) |
| UC3 | External, above ground | Fence rails, cladding, decking boards | Moderate risk (exposed to weather) |
| UC4 | External, in contact with ground | Fence posts, decking sib-structures, retaining walls, agricultural timber | High risk (frequently wet) |
Use Class 4 refers to timber that is in contact with the ground, or frequently wet. Because there is a high risk of decay, treatment must meet strict requirements for both penetration (how deep the preservative goes) and retention.
Disclaimer: as timber is a natural product, various ground conditions and installation methods will affect the durability of timber products.
Want to know more?
The Wood Protection Association, in collaboration with The Timber Trade Association has produced guidance on Use Class and Preservative Treated Wood. Get your copy below.
The Ransfords treatment
At Ransfords, we combine careful species selection, controlled moisture content and robust treatment processes to ensure timber is treated to the appropriate standards – and highways treated timber meets all relevant British standards and highways legislation, ensuring compliance and durability in demanding roadside environments.