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Different classifications make it possible to distinguish wood species according to the use intended for them, and to ensure that the intended conditions of use are adapted to them.

Understand wood classes for DIY

Understanding the use classes of wood species

  • To relate the essence of a wood to its durability, according to its conditions of use, a French standard has defined five distinct classes.
  • In view of this classification, the durability of wood can be natural, or conferred by adequate treatment. So, the same species may be in different classes, depending on whether or not it has been the subject of some type of treatment.
  • In the vast majority of cases, French species can be used in their natural state indoors, without any special treatment. With the exception, however, of the structure, since French regulations require, for wood reserved for this purpose, a fungicidal and insecticidal treatment. And this, whatever the selected essence and the humidity rate.

The 5 classes of wood use

Class I

Location:
Wood to keep dry.
Balance moisture between 6 and 12%, never higher than 20%.
Employment:
Interior joinery: parquet floors, paneling, stairs, doors...
Biological risks:
Insects, termites.

Class II

Location:
Dry wood.
Equilibrium moisture between 12 and 20% and very occasionally over 20% (humidity by condensation).
Employment:
Indoor or protected wood: framing, properly ventilated framing.
Biological risks:
Surface fungi, insects, termites.

Class III

Location:
Humidity frequently greater than 20%.
• IIIA: frequent humidity over a few days with rapid evacuation of water.
• IIIB: frequent humidity over a few weeks with slow evacuation of water.
Employment:
Outdoor wood, without contact with the ground.
Biological risks:
Rot, insects, termites.

Class IV

Location:
Humidity always greater than 20%
Employment:
Horizontal outdoor wood, in contact with the ground or with fresh water, or subject to prolonged or permanent humidification: balconies, terraces, posts, stakes, outdoor furniture.
Biological risks:
Rot, insects, termites.

Class V

Location:
Humidity always greater than 20%
Employment:
Wood in permanent contact with seawater: piers, pontoons, submerged or partially submerged woods.
Biological risks:
Marine borer, rot, insects.

Classes A, B, C, and D for solid wood floors

Class A: occasional or weak passage, without outside access (bedroom, hallway).
Class B: average passage (living room, dining room).
Class C: intense passage (entrance hall, kitchen, living room).
Class D: public places (reception halls, collective offices).

Wear classes

Joinery: the technical and aesthetic classifications of wood: wood

The aesthetic classification of the essences

  • It focuses on knots, flecks, drying checks, bark, resin pockets, the presence of mildew, alterations due to fungi or insects.
  • It allows, when buying a lot or a reassortment, to have parts of very homogeneous quality and without unpleasant surprises.

Joinery: the technical and aesthetic classifications of wood: technical

Detail of aesthetic classes of wood

Class IV

It includes the rejects of other classes. However, the flakes are limited to 20 mm deep, the geometry of the piece must be preserved and the stains of rot must be very limited. This wood is commonly called formwork wood.

Class III

This class is used when the aesthetic aspect is of minimal importance. Any wood rot is excluded, and the presence of black stings must be limited. This wood is commonly referred to as boxwood or pallet.


Class II

Identical to class I with abnormal yarn deviations, slight signs of overheating and blue stain, as well as any type of knot in limited quantity and size, without any risk of altering the resistance of the piece.


Class I

Identical to class 0, with slightly larger and smaller to medium sized nodes. Certain types of less aesthetic nodes, while remaining healthy, are admitted.


Class 0

Insect or fungus alterations and abnormal yarn deviations are excluded. The aesthetic "faults" (knots, checks, pockets...) are small and not very present. Rare quality in large size.

Ecological and water repellent treatment for immersed wood?

I live in Quebec (Canada). I am looking for an ecological protective coating to apply on wooden beams that can be deposited in the water. This product must not contaminate the water and must increase the life of my beams. It can be placed with a rifle (pistol), brush or roller. What do you recommend?
Christian Pessey's answer:
In France, according to the regulations, woods in permanent contact with water must be treated with class 4 (freshwater) or 5 (seawater) treatment. Wood treated with oleothermy (linseed oil, essential oils) best meet your environmental concern, but their use requires a heat treatment (at least 160° C) that is not within your reach. Note that some woods resist very well, without treatment, to immersion, especially the European oak and some exotic woods like the teak or iroko.


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