Sheathing boards are used when constructing framed buildings both in timber and light gauge steel (LSG). The boards provide some structural stability and stiffness to the frame and must undergo racking tests in accordance with BS EN 594. These tests assess the contribution of the boards to the stiffness of the frame.

Even though the boards are usually situated behind cladding and breather membranes, they require testing in accordance with BS EN 12467: Fibre-cement flat sheets - Product specification and test methods, in order to classify them as a Category A type board which is suitable for external conditions. Although this standard is specific to cement fibreboards, it is the only standard available for products like magnesium oxide (MgO) and magnesium silicate boards, amongst others, that do not have prescribed standards.

Testing of sheathing boards to BS EN 12467 allows the boards to be categorised as types A-D as follows:

Category A: Sheets which are intended for applications where they may be subjected to heat, high moisture and severe frost.

Category B: Sheets which are intended for applications where they may be subjected to heat, moisture and occasional frost, e.g. where they are either protected from or not subjected to severe weathering conditions.

Category C: Sheets which are intended for internal applications, where they may be subjected to heat and moisture, but not to frost.

Category D: Sheets for rigid under-layer applications, i.e. tile backer and internal lining boards.

Tests required for categorization are:

• Dimensional
• Density
• Moisture movement
• Bending strength, i.e. modulus of rupture (MOR)
• Water impermeability
• Water vapour permeability
• Freeze thaw plus MOR
• Warm water soak plus MOR
• Heat-rain action
• Soak dry plus MOR.

At Lucideon, we test and verify all types of sheathing boards to ensure compliance with industry standards.