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Standards & Symbols

Standards

What are the most important standards for OSB and timber construction?

Among the many standards referring to wood products and timber, the most important are:

EN 13986:2004: Wood-based panels for use in construction → Characteristics: evaluation of conformity and marking EN 300 (product standard for OSB); Definition: classification and requirements

EN 12369-1: Wood-based panels → Characteristic values for structural design; Part 1: OSB, particleboards and fibreboards EN 1995-1 (Eurocode 5): Design of timber structures → Part 1-1: General rules and rules for buildings

EN 1995-2 (Eurocode 5): Structural fire design of timber structures EN 335 (wood preservation)

EN 120: Determination of formaldehyde content (perforator method)

EN 717-1: Determination of formaldehyde release (chamber method)

EN 13501-1/2: Reaction to fire → Part 1: classification of building materials according to Euro-classes; Part 2: classification of building components (roofs, walls, floors)

EN 12871-1: Wood-based panels → Performance specifications and requirements for load-bearing boards for use in floors, walls and roofs

What are the technical classes of OSB?

Technical classes are the terminology used to describe the different types of OSB boards, according to their intended end use (load & climate conditions).

There are four technical classes: OSB, OSB 2, OSB 3 and OSB 4.

What is the difference between service classes and usage class?

Service classes relate to three defined moisture conditions of the environment. For OSB, they describe the moisture conditions of the environment where the boards are intended to be installed.

The standard EN 1995-1-1 defines the three service classes as follows:

Service class 1 (dry conditions, RH . 65%): Characterized by a moisture content in the material corresponding to a temperature of 200°C and a relative humidity of the surrounding air only exceeding 65% for a few weeks in a year.

Service class 2 (humid conditions, 65 < RH . 85%): Characterized by a moisture content in the material corresponding to a temperature of 200°C and a relative humidity of the surrounding air only exceeding 85% for a few weeks in a year.

Service class 3 (external conditions, RH > 85%): Climatic conditions leading to a higher moisture content than in service class 2.

The usage classes describe the end-use situations of the wood and wood-based panels, in relation to climate. The standard EN 335-1 defines five usage classes. Applicable to OSB are:

Usage class 1 - describes the situations where the wood and wood-based products are used under roof, completely protected from weather and not exposed to wetting.

Usage class 2 - describes the situations where the wood and wood-based products are used under roof, completely protected from weather but where some wetting can occur due to high surrounding moisture.

Symbols & Axis

What is the meaning of the symbols met in standards (tables)?

The most important characteristics and associated symbols related to OSB are:

a) Symbols:

ƒ - strength
E - modulus of elasticity (stiffness)
G - modulus of rigidity
k - retention in strength (kmod) or stiffness (kdef) after a period of time rel. to initial values
t - thickness
p - density
// or 0 - in the direction of the major axis of OSB
or 90 - in the direction of the minor axis of OSB


b) Subscripts:

m - bending
t - tension
c - compression
v - panel shear
r - planar shear
nom - nominal
def - deflection
 

What does major and minor axis of OSB mean?

Unlike particleboards and fibreboards (which show uniform distribution of stress all-over the panel), OSB exhibits different bending and stiffness values on the two dimensions.

Typically, they are 2-2,5 times higher on length compared to width. In this respect:

Major axis = the dimension in the plane of the board in which bending properties have the higher value

Minor axis = the dimension in the plane of the board at right angles to the major axis