| Perhaps the most important consideration in choosing | | | | batu, Western Red Cedar, Merbau, Blackbutt, |
| the lumber species to use for exterior decking is the | | | | Spotted Gum, River Red Gum etc. |
| durability characteristics of the lumber to be used. | | | | The third group, Class 3 is termed "Moderately |
| Unfortunately this is not a precise science as wood is | | | | Durable". Such species will give good service without |
| a natural species, with significant variations even | | | | preservative treatment if clear of the ground and |
| within the same species. For example a species | | | | used in conditions of low termite hazard and involving |
| grown in one country may have significantly different | | | | only intermittent wetting followed by reasonably rapid |
| durability characteristics to the same species grown in | | | | drying. Such timbers can still be used for exterior |
| another country. This may be due to more rapid | | | | decks but it would probably not be advisable to use |
| growth, harvesting at an earlier age or to a lesser | | | | such species in severe weather conditions unless a |
| extent, differences in processing. Furthermore, similar | | | | maintenance regime involving the application of good |
| species may have sub-species which could exhibit | | | | quality decking oil is carried out at regular intervals. |
| totally different durability characteristics. | | | | Species in this group include Cambara, Kempas, Karri, |
| Due care should be taken that any wood does not | | | | Eucalyptus saligna. |
| contain the outside sapwood. Sapwood of most | | | | The final group Class 4 is termed "Non Durable". |
| hardwood species is non durable and will decay quite | | | | Timber species in this group are considered unsuitable |
| rapidly even if the heartwood itself is rated as highly | | | | for exposed decking because of their low natural |
| durable. With some cypress species in particular, the | | | | durability. |
| sapwood is prone to decay extremely quickly. | | | | But apart from resistance to the ravages of sunlight, |
| Fortunately sapwood is generally a lighter color, so | | | | rainfall and humidity, in many locations there is |
| can be reasonably easily distinguished. | | | | another factor to consider - termites. There is no |
| To a large extent, the denser, harder lumber species | | | | direct correlation between durability and resistance to |
| generally possess higher durability properties. These | | | | termite attack so care needs to be taken in termite |
| are often referred to as Class 1 or "Highly durable". | | | | prone areas. Suitable species with high resistance to |
| Examples of such species includes Ipe, Cumaru, | | | | termite attack would include Ipe, Cumaru, Jatoba, |
| Tallowwood and Ironbark. Under normal conditions, | | | | Teak, Jarrah, Selangan batu etc. |
| not in permanent contact with water, such species | | | | Finally and perhaps of lesser importance is that the |
| can be expected to resist decay and insect attack | | | | lumber chosen should not twist, cup or deform in |
| for at least 25 years and up to 50 years. | | | | service. This requires some skill and experience on |
| The next group is Class 2 where the lumber species | | | | the part of the lumber mill as the majority of |
| are termed "Durable". Lumber species included in this | | | | hardwoods require carefully controlled kiln drying to |
| group also exhibit exceptional durability characteristics | | | | bring the moisture content of the wood down from |
| and the wood can typically be expected to have life | | | | more than 25% with freshly cut timber to |
| of 15 to 25 years or more. Some species in this | | | | approximately 16%. If the timber is dried to fast it |
| group closely approach the performance of the Class | | | | can crack and twist when in service. Even when |
| 1 timbers even under severe conditions of service | | | | properly kiln dried, all timber will expand and contract |
| and in fact all species in this group may be regarded | | | | to some extent in service particularly in damp |
| as approximating the service of Class 1 timbers | | | | conditions. In such conditions, a timber species with a |
| where conditions are less severe, as in typical | | | | low shrinkage rate may be preferable. Such species |
| decking. | | | | would include Ipe, Selangan batu, Merbau and Teak |
| This group includes a large range of species including | | | | amongst others. |
| Teak, Jarrah, Jatoba, Bongossi, Purpleheart, Selangan | | | | |