If you are building a new home or timber decking for your current Brisbane home, you will want to pay close attention to durability ratings. Imagine building a home and finding out you need to replace most of the framework in 20 years because you used a variety of timber with an insufficient durability rating.
Factors to Consider
Timber ratings are, by nature, inexact. There are so many factors such as climate, usage and location that it is impossible to derive an exact estimate of any timber or project’s “shelf life.” There are many timber buildings that are over 100 years old and still standing. However, there is no species of timber that has durability rating of close to 100 years.
Timber ratings are based on a range of numbers that take light usage to heavy usage and friendly climates or detrimental climates into consideration.
The Rating System
The rating system is according to Australian Standard AS-5604-2005, Timber—natural durability ratings. It is based on the average life expectancy of sound, untreated hardwood measuring 35 mm x 35 mm for testing conducted above ground and 50 mm x 50 mm for testing conducted in the ground.
However, it is extremely important to remember that these are average ratings. There are a number of factors that affect durability of timber besides its intrinsic natural durability rating. Treatment can extend the life of timber, especially beneath the ground. The manufacturing process plays a role, as do supplementary maintenance and protection. The size of a beam can help determine its lifespan, as can its immediate environment and climate.
Class 1 timber can be expected to perform over 40 years above ground and over 25 years underground. Class 2 timber can be expected to perform between 15-40 years above ground and 15-25 years underground. Class 3 timber is rated at 7-15 years above ground and 5-15 years underground. Class 4 timber is rated at 0-7 years above ground and 0-5 years underground.
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