Outdoor Timber Print E-mail
For external applications such as cladding, decking, pergolas, landscaping, fencing and the like, timber can be an attractive and practical choice. If the correct type of timber is not used in certain outdoor applications, it sometimes fails to perform to user expectations. In most cases this is not the fault of the material but rather as a result of a lack of understanding of the various species of timber, their suitability and their installation and maintenance.

Timber species are rated into 4 classes of durability for use in-ground contact and 4 classes of durability for use outside above ground, with Class 1 being the most durable and Class 4 the least durable. (See: Natural Durability Ratings) Ideally, timbers for external application should be chosen from Durability Classes 1 or 2 where their natural durability would provide an expected service life in-ground contact of at least 15 years and if outside above ground and properly maintained, a much longer service life. Timbers of Durability Classes 3 and 4 can be successfully used outside above ground so long as care is exercised in detailing of joints, nailing or fixing and adequate coating and maintenance is carried out.

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Timber paving
Alternatively, preservative treated timber may be more appropriate than the lower durability species for external applications. Treated timber is a timber product that has been treated with a preservative to improve the timber's resistance to attack by wood destroying fungi and wood destroying borers and termites. In other words, the timber's durability is enhanced to a level which is suitable for use in an intended application. However, the "treatment" does not afford the timber protection against weathering.

Preservative treated timber has a service rating known as the Hazard Level Guide which rates the hazardousness of the exposure level (and therefore the amount of hazard protection required) from H1 being the lowest, to H6 being the highest. (See: Treated Timber) As an example, treated timber for decking (i.e. above ground application) should be level H3 and fence posts or pergola posts (those set in-ground) should be H4. There are many different types of treatment methods and preservatives used and therefore an understanding of the application and the service condition need to be considered prior to selection. (See: Treated Timber) As with non-treated timber, protection from weathering should be made as treated timber will deteriorate when exposed because the treatment offers protection only from fungi and insect attack as previously noted.

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Timber elevated walkways
Remember, with treated timber:
  • Most of the treated timber used externally will only have an envelope of treatment although some pieces may be completely penetrated.
  • When using treated timber a "brush on preservative" should be applied to all cut surfaces, rebates, checkouts and the like.
  • It is poor practice to purchase larger sized pieces of treated timber and then rip them into smaller sized pieces.

In many parts of Australia, the construction of new buildings and additions to existing buildings will be assessed as being in a Bushfire Prone Area. The relevant Australian Standard - AS 3959 - provides for a range of Bushfire Attack Levels for proposed construction. Each Level is based on the assessed threat and as the assessed threat increases, so do the restrictions on the building materials that may be used. Where there are restrictions on the building materials, timber is permitted in the lower levels provided the timber species meets certain criteria. (See: Construction in Bushfire Prone Areas)

Timber Fences
(PDF, 0.9 MB)
Australian Timber Importers Federation
Timber Information Bulletin 2 - Handrails and Balustrades
(PDF, 0.8 MB)
Australian Timber Importers Federation
Timber Users Guide 1 - Timber, Durability & External Applications
(PDF, 0.1 MB)
Australian Timber Importers Federation
Timber Users Guide 2 - Protective Coated Pine
(PDF, 0.1 MB)
Australian Timber Importers Federation
Timber Users Guide 4 - Imported Hardwood Decking Specifications
(PDF, 0.1 MB)
Forest & Wood Products Australia
Timber Preservers Association of Australia
The Timber Preservers Association of Australia (TPAA) represents the nation's timber preservation industry. It is an organisation comprising timber treaters, suppliers of preservatives, research organisations, as well as individuals and bodies having an interest in timber preservation.
 
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