ISO 21887:2007定义了五种用途类别，它们代表了木材和木质产品在世界各地可能暴露的不同使用情况。还为这些使用类定义了子类。 ISO 21887:2007仅适用于木材和木制品的防腐剂和预处理工艺，不适用于补救和消除现有木材损坏的产品和工艺。ISO 21887:2007的附录提供了使用分类的指南，以指定防腐处理、处理过的木材、天然耐用木材和改性木材，但未提供最终规范。

ISO 21887:2007 defines five use classes that represent different service situations to which wood and wood-based products can be exposed all over the world. Subclasses are also defined for these use classes. ISO 21887:2007 applies only to preservatives and processes for pre-treatment of wood and wood products and is not intended for products and processes for remediation and eradication of existing damage to timber. The annex to ISO 21887:2007 provides guidance on applying use classification to specify preservative treatments, treated wood, naturally durable and modified wood but does not provide definitive specifications.