Issue of wood service life

according to ARA standards and rules.

For determining the durability of wood species, there are two standards: ČSN- EN 350-2 and ČSN – EN 335-1. ČSN-EN 350-2 evaluates the resistance of wood species to fungi and other insects on a scale from 1-5 and is at least some guide in the selection of wood species for outdoor use. From our point of view, its scale does not sufficiently distinguish between the use of wood and the quality of wood according to the place of growth and other qualitative factors. ČSN-EN 350-2 deals with the occurrence of biological agents according to use classes.

Both standards are a good guide, but it is not easy for a layman to gather all information that is needed and draw adequate conclusions. For this reason, we have developed our own classification of the use of wood species on the basis of many years of knowledge. It is always necessary to consider the specific construction and carefully select both wood species and individual construction details. The following tools may be helpful for proper wood selection.

Our recommendations are:

  • It is important to first consider the wood service life you want to achieve. We use the following evaluation with an estimated wood service life for individual constructions and wood species. Recommendations for individual wood species and constructions can be found in the following table.
Our recommendation Maintenance-free wood service life
Excellent over 40 years
Suitable 15 – 30 years
Not recommended 10 – 15 years
Not suitable less than 10 years
Fundamentally not recommended less than 5 years
  • Determining use of wood – construction type for wood selection. The speed at which water from a particular structure and its surface and joints can drain or dry out and how much it is exposed to UV radiation is crucial for wood service life. We distinguish structures as follows:
    • Vertical structures- distinction between a modern design or traditional construction – usually different types of wood sidings, window linings, etc.
    • Horizontal structures – mostly different types of wooden terraces.
    • Sun shading – various types of window shutters and blinds.
    • Contact with soil, fence pegs, garden stairs, pond piers.
  • Selection of construction details.
  • Surface finishing. Different types of finishes have been used since time immemorial. It is deep-rooted in our minds. The conditions for the use of wood and thus also for surface finishing have changed significantly in recent decades. Above all, the ways in which trees are used have changed, from structures with traditional principles and techniques to modern designs. At first glance, it seems that the development of coatings has also changed significantly, but this is only true to a limited extent. In particular, modern architecture has begun to load wooden constructions and thus also coatings in different ways, and in many cases, coatings are not able to withstand this load. With this comes the need for intensive maintenance, which is not free of charge and in some cases, it is not possible to perform it technically correctly at all. One such example can be horizontal wooden structures, where in principle it is not possible to ensure that water and UV radiation do not disturb the cohesion of coated wood. Our opinion is that it is first necessary to choose sufficiently durable wood and only then to consider reasons for coating. The opposite way, i.e. increasing the resistance of wood by coating, especially with horizontal structures, does not work. In addition, coatings are not environmentally friendly, even the water-soluble ones.
  • Durability of wood species – among other things, durability is significantly affected by the place and method of growing trees. Simply speaking, no two Siberian larches are the same. Selecting suppliers according to place of logging and method of cutting are practically impossible for a layman. It is helpful to avoid wood species with significantly variable quality (Banghkirai, RED Meranti, Siberian larch, oak, etc.). Always use more durable wood, where these deviations affect the service life less. The price can be a guide to some extent, the number of annual rings per 1 cm, other visible defects, knots, cracks, twisting. Simply put, first-rate wood at a low price does not exist in global markets. You usually buy poorer quality due to the place of growth, often from young trees and from various illegal logging places and imports. Low prices are not for free.
  • Economic pie. Make an economical pie that represents how much the whole structure will cost you, and only then think about reasonable savings. Separately calculate how often and for how much money you will do maintenance. If you are honest with yourself, you will be surprised by the result.