Perhaps the most important consideration in choosing the lumber species to use for exterior decking is the durability characteristics of the lumber to be used. Unfortunately this is not a precise science as wood is a natural species, with significant variations even within the same species. For example a species grown in one country may have significantly different durability characteristics to the same species grown in another country. This may be due to more rapid growth, harvesting at an earlier age or to a lesser extent, differences in processing. Furthermore, similar species may have sub-species which could exhibit totally different durability characteristics.

Due care should be taken that any wood does not contain the outside sapwood. Sapwood of most hardwood species is non durable and will decay quite rapidly even if the heartwood itself is rated as highly durable. With some cypress species in particular, the sapwood is prone to decay extremely quickly. Fortunately sapwood is generally a lighter color, so can be reasonably easily distinguished.

To a large extent, the denser, harder lumber species generally possess higher durability properties. These are often referred to as Class 1 or