Treated timber for a log store: ask for the Use Class

Ask what end use the treatment is specified for. “Treated green timber” is a description, not a complete durability specification.

Use Class is about exposure

The Wood Protection Association's current buyer guidance places uncoated exterior timber above ground in Use Class 3 and timber in ground contact in Use Class 4. Structural support and repeated wetting can raise the requirement. Tell the merchant exactly where each member will sit and ask for written confirmation of Use Class and desired service life.

For a well-detailed store, posts, rails and slats should stay above ground and drain freely. Feet or members that touch soil need a product specified for that exposure; brushing preservative onto ordinary internal timber is not equivalent to industrial treatment.

Cross-cuts expose untreated zones

Plan cuts before assembly and follow the treatment supplier's instructions for end-grain protection. Put cut ends where they can drain and avoid upward-facing pockets. Drilling and notching should not create water traps.

Treatment does not replace detailing

Keep the base drained, add roof overhang and make joints shed water. Even durable material lasts better when it can dry. Do not bury post bottoms in mulch or let bark pile against them.

Keep chemicals off firewood

Use products according to their label and let finished components dry or cure as directed before loading. Do not coat the fuel itself. Wear the required protective equipment when cutting treated timber and dispose of offcuts responsibly.

Sources

• WPA buyer's guide to preservative-treated wood, issue 7 — Use Class 3 and 4 applications, checked 10 November 2026.
• TDCA: timber preservation — written specification and end-use guidance, checked 10 November 2026.