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Treated Roundwood

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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.

Treated roundwood
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.

Learn more
You can find out more detailed information about roundwood here.

Fencing

The inherent appeal and strength of timber makes it the obvious choice for fencing. Timber fencing not only provides a natural look in keeping with the outdoor environment but it also enables the construction of a long lasting, durable property boundary. Fences come in many forms including the traditional paling, picket, post and railing styles. Most rely on a structural frame of posts embedded into the ground and two or more rails spanning between the posts. The ultimate selection of a suitable fence type or style is determined by application and aesthetics. A fence can serve a variety of purposes, including the provision of security, privacy and safety in addition to defining property boundaries. Specification for durability is important, especially for posts, given their exposure to high moisture in the ground.

This section provides an overview to best practice methods in specifying, installing and finishing a timber fence.

Portal Frames

Timber portal frames are one of the most favoured structural applications for commercial and industrial buildings whose functions necessitate long spans and open interiors. As a material choice, timber offers designers simplicity, speed and economy in fabrication and erection.

Timber portal frames offer a strong, sound and superior structure. Structural action is achieved through rigid connections between column and rafter at the knees, and between the individual rafter members at the ridge. These rigid joints are generally constructed using nailed plywood gussets and on occasion, with steel gussets.

From material selection to finishing, this application guide provides a comprehensive overview of the process of using timber in the specification, fabrication and erection of portal frame structures.

Retaining Walls (Landscaping)

The natural appeal, strength and versatility of timber makes it an ideal choice for retaining wall landscaping applications.

Retaining wall systems include cantilevered round or sawn timber, mass wall and crib wall construction. Walls up to one metre in height follow a basic design and can usually be constructed using standard proprietary wall systems. An engineer will be required to plan and design walls greater than one metre, including the footings and drainage.

Drainage of retaining walls is a critical factor in influencing the long term stability of the wall and should thus form a significant part of the design and planning process. 

Regular care and maintenance of retaining walls is essential in ensuring the long-term stability and safety of the structure.

Structural Timber Poles

Timber pole construction is typically utilised to provide support for gravity loads and resistance against lateral forces. The natural appeal of timber ensures that its role is not purely structural however, with timber poles complimenting architectural designs aimed at harmonisation with the natural environment. The small number of footings required in pole frame construction also ensures minimal disturbances to the site.

With a double bearer system, poles can be spaced further apart than is usual, creating a more spacious building interior, that allows greater interior design flexibility. While poles are usually placed in a grid like system this is not compulsory and the flexibility of the application means the system can cope with a wide variety of designs, enabling designers to take full advantage of beautiful outlooks.

This article provides a comprehensive overview of the process involved in specifying, designing and constructing a solid timber pole construction.

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