Roundwood is any timber product supplied in log form; more commonly known as poles, piles, girders and posts. Roundwood is mainly used for structural applications and its main benefit is that it requires very little processing and that it also retains it density and strength, unlike sawn timber.
Most treatment methods for roundwood are designed to deliver preservative in the ring of sapwood. Removal of bumps to improve the aesthetic appearance of the round timber should be avoided if the underlying heartwood is not of high durability.
For hardwoods where the timber is exposed to the weather or there is in-ground contact, the sapwood is normally either removed or preservative treated.
For softwoods, preservative treatment is necessary because most of the softwoods commercially available for round timbers have a low durability rating. Pine poles readily accept treatment, are lighter and have a proven history in pole structures. However, small diameter pines are less dense and therefore not as strong.
CCA (Copper Chrome Arsenate) is the most common preservative treatment for poles, while PEC (Pigmented Emulsified Creosote) may also be used. Supplementary treatment may be required at around 5-year intervals, especially in more tropical areas.
Treatment requirements for roundwood applications
Roundwood is often used for in-ground contact or is exposed to the weathering, so the following requirements should be considered:
- Poles in-ground contact - only timber of Durability Class 1 should be used or poles containing sapwood that can be pressure preservative treated to an H5 level. Plantation softwood should also be treated to H5 level.
- Poles mounted on stirrups or stools which are clear of ground contact - only timber of Durability Class 2, or an H3 level of preservative treatment are acceptable when used in an exposed situation. When used in a protected situation, any Durability class of timber can be used, provided any lyctid susceptible sapwood is treated to an H1 level.
- Poles on base plates - exposed (subject to regular wetting) - timber should be de-sapped Durability Class 2 or better; or Durability Class 2 or better with sapwood treated to H3 level. Plantation softwood should be treated to H3 level
- Poles on base plates (protected by the building but may receive occasional wetting) - Timber species can be of any Durability Class but any lyctid susceptible sapwood should be treated to an H1 level.
Enclosing a pole or post in concrete to give added support may actually cause decay as concrete retains moisture and makes it difficult to provide further treatment of the soil.
The tops of poles, treated or untreated, should be fitted with a metal cap to prevent water entry.
You can find out more detailed information about roundwood here.