Usage classes of wood

Wood is a versatile and sustainable building material, but not every type of wood is suitable for every application. The suitability of wood for certain environments is determined by, among other things, usage classes. These classes indicate the extent to which wood is exposed to moisture and weather influences, which directly influences the durability and lifespan of the material. This article discusses the different usage classes and their applications.

User classes and their characteristics

The European standard (NEN-EN 335) defines five use classes for wood and wood products. This is to tell where and what it can be used for. Often a type of wood falls into different use classes because of the different applications it is used for.

Usage class 1: Indoor, dry

Wood in this class is used exclusively indoors, where it is not exposed to moisture. Examples include furniture, interior doors and floors. The risk of mould infestation is minimal in this class.

Usage class 2: Indoor, occasional moisture

Wood in this class is also mainly used indoors, but can occasionally come into contact with moisture, for example through condensation. Think of roof constructions or joists in buildings where some moisture occurs.

Usage class 3: Outdoors, exposed to the elements

This wood is used outside and is exposed to weather influences. A distinction is made between:

Usage class 3.1: Wood that is used above ground and does not become permanently wet, such as cladding.
Usage class 3.2: Wood that regularly gets wet, for example in pergolas or garden wood.

Usage class 4: Contact with soil or water

Wood in this class has direct contact with the ground or fresh water, which means it has a high risk of being attacked by fungi and insects. Examples include decking, fences and posts. Often impregnated or naturally sustainable wood is used for this.

Usage class 5: Contact with salt water

This class includes wood that is in permanent contact with seawater, such as jetties and harbour structures. This wood must be extremely durable to withstand the harsh conditions.

Durability classes versus Usage classes

In addition to usage classes, there are also durability classes, which indicate how well a type of wood is resistant to biological attack. This is laid down in the European standard NEN-EN 350.

Sustainability classes range from 1 (very durable) to 5 (not durable) and indicate the natural resistance of untreated heartwood to fungi and wood-destroying organisms.
Usage classes indicate the extent to which wood is exposed to moisture and biological attack in different environments.

A type of wood with a high durability class may be suitable for a higher usage class without additional treatment. Less durable types of wood may require preservation to make them suitable for certain applications.

Which wood for which application?

When choosing wood for a project, it is important to consider the correct use class. Tropical woods such as Azobé and Bilinga are naturally suited to higher use classes (4 and 5), while softwoods such as Oregon Pine and Douglas often need to be treated to achieve the same durability.

Conclusion

By choosing the right usage class of wood, you extend the life of the material and prevent premature wear or deterioration. Whether you are laying a wooden floor indoors or installing a deck outdoors, understanding usage classes helps you make the right choice for a sustainable result.

Need inspiration?

Our clients have realised wonderful projects. Do you have a question? Then take a look at our knowledge base or take contact with one of our specialists.

See more projects