The long performance of engineered timber structures can be affected by exposure to various environmental hazards. While timber is largely inert to chemical contamination that may cause steel to rust, insect and fungal attack is possible under some conditions.

To protect from these conditions modern treatment methods can ensure durability. The attached table identifies the various conditions from interior use (where insect / termite hazards might exist) to marine exposure. The hazard levels are described and appropriate treatment levels detailed.