Types of Treated Timber

4 grades or types of treated timber are commonly used:
H3 treated timber is suitable for use above ground on structures such as pergolas.
H4 treated timber is designed for ground contact and is used for fence posts and in general landscaping work.
H5 treated timber must be used for the poles used in constructing pole homes, retaining walls that require the services of a structural engineer (see Before You Build a Retaining Wall for more information) and other structural components that come into contact with the ground.
H6 treated timber is primarily used for constructions where the timber will be fully or regularly immersed in seawater, such as marine pilings and jetty bracings.

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