Tech Terms

Use class

The Use class determines whether a panel requires preservative treatment or other protective measures to achieve the desired service life. 

Use classes are defined in EN 335 Durability of wood & wood-based products. Five Use classes are defined, for construction purposes, Use classes 1 to 3 are the most important,

Use class 1 - Under cover, fully protected from weather and not exposed to wetting.

Use class 2 - Under cover and fully protected from the weather but where high environmental humidity can lead to occasional but not persistent wetting.

Use class 3 - Not covered and not in contact with the ground. Either continually exposed to the weather or protected from the weather but subject to frequent wetting.

Use class 4 - In contact with the ground or fresh water and thus permanently exposed to wetting.

Use class 5 - Permanently exposed to salt water.

NOTE: 9.2 of EN 636:2012+A1:2015 Plywood - Specification, Requirements for plywood for use in exterior conditions (Use class 3), Biologocal durability, reads, the performance of most plywood will be compromised if suitable preservative treatment and/or relevant surface and edges coating is not applied and if the panels are not properly maintained and installed.

In summary, unless stipulated otherwise, it is necessary in all instances to ensure that any exterior grade panels being used in exterior applications (Use class 3) are fully coated with a suitable treatment prior to installation, on both faces and all edges, including those edges cut on site.