There are a number of different poles and piles available. The best type to choose depends largely on the required application and how significant their exposure to the elements, including ground contact, will be. These include:

• Naturally durable poles and posts: Timber in ground contact is always a Use Class 4 application which means that only wood species defined in EN.350 as Durability Class 1 – very durable or Durability Class 2 durable, from which all sapwood has been removed should be used in these applications.
• UC4 Treated Poles: These are timber poles, often round in shape, that are typically used in fencing and outdoor landscaping applications. As they come into contact with the ground, they must be UC4 treated to ensure durability and longevity (see treatments below).
• UC4 Round Posts: These are round timber posts that usually have a sharpened point at the bottom to aid installation into the ground. Used throughout the landscaping and agricultural sector as they come into contact with the ground, such posts must be UC4 treated to ensure durability and longevity (see treatments below).
• Creosoted Poles: These are available as an alternative to UC4 treated poles and posts, and are often used to hold electricity and telephone cables, as well as for other exterior projects. The poles are treated with creosote to help preserve the timber and protect it against weather, fungi and insects that may otherwise cause the wood to rot. Typically Creosoted poles will have a desired service of 30 or 60 years.

Creosote alternatives: Other types of preservative treatments have been developed to offer the extended desired service life of 30 or 60 years on poles and posts. Talk to a TDUK specialist supplier for more information on the branded products available.

• UC3 Rails and Show Jumps: Timber is a common material used for rails and show jumps in the equestrian and horse-riding industries. Because these items do not come into direct contact with the ground, UC3 treated timber can be used, rather than UC4 (see treatments below).

In the UK There are no softwoods and very few temperate hardwoods that are suitable for in ground contact applications without some form of preservative treatment (DC 1 or DC 2) European Oak being an exception. The more durable tropical hardwoods such as Greenheart, and Ekki are used for civil and marine applications but are generally brought to the UK as square or rectangular sections.

This means the most common species used for poles and piles will be those most amenable to accepting preservative treatments such as Pine. More resistant species such as, Spruce and Douglas Fir, will require additional techniques such as incision in order to achieve the necessary preservative penetration for Use Class 4 applications

Softwood poles and piles require pressure-impregnation with standard Use Class 4 preservative treatments, which usually has a 15-year service life, but longer service lives of 30 or 60 years are available from  suppliers providing Creosaote or the alternatives that have been developed . Once applied at the factory, this treatment gives the timber the required durability and protection against moisture ingress from external elements, as well as against insects and fungi that may otherwise cause rotting.

UC3 preservative treatment is sufficient for any timber poles and piles that do not come into direct ground contact.

BS EN.350 – Durability of wood and wood based products. This standard sets out Durability Class descriptions as below and provides a list of species showing their durability class.

• DC 1 Very durable
• DC 2 Durable
• DC 3 Moderately durable
• DC 4 Slightly durable
• DC 5 Not durable

The minimum standards for the treatment of wood are set out in British Standard BS 8417 and the Wood Protection Association (WPA) Code of Practice – Industrial Wood Preservation (June 2021). In these standards the level of treatment is tailored to the application ‘Use Class’ of a wood product as defined in BS EN 335 (Durability of wood and wood-based products).