Summary
• BS 8417 calls for a treated timber basic service life of 15 years.
• Timber in ground contact should have Use Class 4 protection.
• The Highways Agency requires timber to have a 30-year service life.
• Both the customer and the treatment supplier have obligations.n BS 8417 calls for a treated timber basic service life of 15 years.

“Under normal conditions, the life expectancy shall be 15 years, subject to the maintenance recommended by the manufacturer, where prescribed. If longer service life is required, up to 30 years, this shall be specified.” So says BS 8417, which relates to preservative treatments for timber.

It’s reasonable to expect treatment companies to be able to provide the basic 15-year desired service life for all fencing timbers, but it also behoves the customer to be clear in specifying what is required at the time of order.

For example, to provide this level of protection it should be noted that for timbers in ground contact, the customer should always specify Use Class 4 protection (Use Classes are defined in BS EN 335-1) and, for those not in ground contact, such as arris rails and feather edge boards, then Use Class 3 protection is sufficient.

Certificate of treatment

The customer should also ask the treatment company for a certificate of treatment which must show the date treated, the Use Class of treatment and a pack number fixed to the individual batch of timber to enable a delivery check to be made. The description and quantity of pieces in the pack must also be shown on the certificate.

It is the treatment company’s responsibility to ensure that, in order to comply with the customer’s order, the correct timber species is used – for example, treated unseasoned spruce posts are unlikely to provide the desired 15-year service life, let alone 30 years, so it’s important to check on the treatment certificate what species has been supplied and treated.

Highways Agency

The Highways Agency – and many local authorities and utility companies – require a higher level of treatment, providing a service life of up to 30 years and treatment companies wishing to secure these contracts must have a Sector Scheme 4 Quality Management Certificate.

They must also be able to prove to a third-party organisation, such as BSI or BM TRADA, that their treatment plant operators have NVQ level 2, that the preservatives and processes used comply to the required British Standards and, most importantly, that the species treated are correct for their intended end use.

Sector Scheme 4 also requires the treater to demonstrate, through regular sampling, that the treatment has achieved the correct preservative penetration depth and has the correct amount of chemical in the treated zone.