Timber used in exposed to weather conditions needs to have two main attributes. Required strength and required durability. Just because hardwood timber is specified as a high strength hardwood such as ‘F27’, it does necessarily mean it has high natural durability. For exposed to weather applications (i.e. deck bearers, joists balustrades and posts etc.), Above Ground Durability Class 1 should also be specified as well as strength class. Typical suitable species are spotted gum, ironbark and also for imports, kwila/merbau.