EN 335:2013

Durability of wood and wood-based products – Use classes: definitions, application to solid wood and wood-based products

This 2013 edition of EN 335 supersedes EN 335-3:1995; EN 335-1:2006 and EN 335-2:2006 as all three parts have now been combined into one document. Unfortunately, this revision of EN 335 removed the information giving the application of Use1 Classes to the various types of wood-based panels. Many sectors of the European panel industry consider this to be a detrimental omission, so APA has elected to maintain the original guidance given in EN 335-3:1995 for OSB. For Plywood only this information is now given in Annex B of EN 636:2012+A1:2015. Guidance on LVL and Use Classes given by APA (but which did not form part of the EN 335-3:1995) has also been kept.  This information can be found on this website at EN 335-3 (now withdrawn).

Note:1 The term ‘Hazard Class’ used in EN 335-3:1995 (now withdrawn) has been replaced by ‘Use Class’ in EN 335:2013.

Compared to EN 335 Parts 1-3, the main modifications to EN 335:2013 are:

1) The former three parts have now been combined.

2) Sub-classes 3.1 and 3.2 have been redefined.

3) The sub-division of Use Class 4 has been omitted.

 

EN 335:2013 gives general definitions of Use Classes for different service situations and is relevant to solid timber and wood-based products. It gives information on the biological agents that can attack wood and wood-based products in defined situations.

Different Use Classes and Occurrence of Biological Agents

Use

Class

Definition

General Service Conditions

Occurrence of Biological Agents1

Disfiguring fungi

Wood-destroying fungi

Beetles

Termites

Marine borers

1

Situation in which the wood-based product is inside a construction, not exposed to the weather and wetting. Interior, dry

Everywhere in Europe & EU territories Locally present in Europe & EU territories

2

Situation in which the wood-based product is under cover and not exposed to the weather (particularly rain and driven rain) but not persistent, wetting can occur. Interior, or under cover, not exposed to the weather. Possibility of water condensation. Everywhere in Europe & EU territories Locally present in Europe & EU territories

3

Situation in which the wood-based product is above ground and exposed to the weather (particularly rain)2. Exterior, above ground, exposed to the weather. Everywhere in Europe & EU territories Locally present in Europe & EU territories

When sub-divided:
3.1 Limited wetting conditions
3.2 Prolonged wetting conditions

4

Situation in which the wood-based product is in direct contact with ground and/or fresh water3. Exterior in ground contact and/or fresh water. Everywhere in Europe & EU territories Locally present in Europe & EU territories

5

Situation in which the wood-based product is permanently or regularly submerged (i.e. sea water and brackish water). Permanently or regularly submerged in salt water Everywhere in Europe & EU territories4 Everywhere in Europe & EU territories4 Everywhere in Europe & EU territories
Notes:
1 It may not be necessary to protect against all biological agents listed as they may not be present or economically significant in all service conditions in all geographical regions, or may not be able to attack some wood-based products due to the specific constitution of the product.
2 Decay risk depends on the climate and other in-use conditions (temperature, relative humidity, structural conditions, design details and maintenance provisions).
3 Wood-based products which are constantly below water level or completely buried and fully  saturated by water are not susceptible to be attacked by fungi but may be damaged by bacterial decay.
4The above water portion of certain components can be exposed to all the above biological agents.

Informative Annex A provides guidance on aligning the three Service Classes given in Eurocode 5 (EN 1995-1-1) and the five Use Classes given in this standard as the two systems used different criteria to achieve different results.

Service Classes are used by designers when assigning strength values and calculating deformations for wood-based products used in structural applications.  These Service Classes are determined by the wood moisture content corresponding to the relative humidity and the temperature which are expected to prevail in service.

While moisture content is also important in biological durability, the system of Service Classes in Eurocode 5 and the system of Use Classes in this standard differ in their consideration of the effects of this moisture, so individual classes do not directly align with one another.

The table below gives guidance on the possible corresponding Use Classes for each of the Service Classes.

Service Classes and their possible corresponding Use Classes

Service Class according to Eurocode 5

Possible corresponding Use Class according to         EN 335:2013

Service Class 1 Use Class 1
Service Class 2 Use Class 1
Use Class 2 if the component is in a situation where it could be subjected to occasional wetting caused by e.g. condensation
Service Class 3 Use Class 2
Use Class 3 or higher if used externally