Strength classes
of glued laminated timber

According to DIN EN 14080, glued laminated timber is divided into different strength classes. During production, all lamellas are visually or mechanically sorted in order to assign them to a (tensile) strength class (criteria here are, for example, knots and annual ring width in the case of visual sorting and gross density and modulus of elasticity in the case of mechanical sorting). Furthermore, the finger joint of the lamellas determines the strength of the glued laminated timber.

The designation of the strength classes of glulam begins with the letters “GL” (glued laminated timber) and the following number indicates the bending strength. The letter at the end indicates whether the cross-section is homogeneous (h) or combined (c). Homogeneous glulam consists of lamellas of the same (tensile) strength class over the entire cross-section.

Combined glulam consists of lamellae of a higher strength in the edge areas of the cross-section than in the inner area. This layered structure is particularly useful for bending beams, as here the edge areas are subject to high tensile or compressive stress. This enables efficient use of the material.