Overview
ISO 21887:2007 - Durability of wood and wood-based products - Use classes defines a simple, internationally-applicable system of five use classes (with further subclasses) that describe service conditions for wood and wood-based products worldwide. The classification is based on exposure to moisture, soil and the biological agents (insects, decay fungi, marine borers, etc.) that cause degradation. ISO 21887:2007 applies only to preservatives and pre-treatment processes for wood and wood products; it is not intended for remediation of existing timber damage. An informative annex provides guidance on applying the use classes to specify preservative treatments, treated wood, naturally durable and modified wood, but does not give definitive numeric specifications.
Key Topics
- Five use classes (1–5) that rank environments from least to most biologically aggressive:
- Class 1: Interior, dry (protected from weather; wood-boring insects may be relevant)
- Class 2: Interior, occasional wetting (decay fungi or discoloration may occur)
- Class 3: Exterior, above ground (protected or exposed variants: 3.1 / 3.2)
- Class 4: In ground or fresh water contact (subclasses 4.1 / 4.2 reflect soil aggressiveness)
- Class 5: Marine exposure, regular salt-water immersion (subclasses 5A/5B/5C for regional borer threats)
- Subclasses address regional and situational variations (e.g., termite prevalence, aggressive soils, limnoria resistant to creosote).
- Definitions of “protected” (protection against wetting or weathering by design or coatings).
- Scope limitation: standard targets pre-treatment and preservative specification, not post-damage remediation.
- Guidance on how to integrate use classes into national and regional standards and trade practices (annex covers WTO/TBT considerations).
Applications
ISO 21887:2007 is practical for:
- Specification of preservative treatments and pre-treatment processes for new wood products.
- Product design and material selection, helping architects and engineers choose appropriate species, treatments or modified wood for the expected exposure.
- Manufacturers and treatment plants to classify treated timber for intended service conditions and communicate suitability to buyers.
- Regulators and procurement when defining durability requirements for infrastructure, decking, marine works, poles and outdoor joinery.
- Standards bodies and testing labs as a harmonized framework to align national/regional preservation rules with international practice.
Related standards
ISO 21887:2007 is a framework intended to be used alongside regional and national standards on:
- preservative performance and application methods,
- durability testing and classification,
- treated wood marking and labelling.
Users should consult relevant national/regional treatment specifications and test-method standards when applying the ISO 21887 use classes.
