This paper discusses strengthening of glued-laminated timber in tension perpendicular to the grain. Wood properties are often inappropriate for high performance structural applications. Major drawbacks like durability and high variability can be reduced by using glued-laminated timber. A further step to decrease the variability is to strengthen the cross-section to prevent tensile failure perpendicular to the grain. This has been widely investigated during the last decades by bonding fibre reinforced polymer (carbon, aramid and glass fibres) to timber or glulam beams, with mostly promising results. However, a great concern about environmental friendly materials showed up a few years ago. Mineral and petrol-based fibres are difficult to recycle and increase the amount of carbon dioxide in the atmosphere leading, for instance, to the preoccupant greenhouse effect. Natural fibres such as flax are on the contrary, recyclable and CO₂ neutral. Their low density and high specific mechanical properties provide great advantages for timber construction.

Specimens of glued-laminated timber with a volume of 0.01 m³ have been reinforced with fibre reinforced polymer (FRP) composites, and tested in tension perpendicular to the grain. Unidirectional laminates have been prepared with flax and glass fibres. Epoxy resin, which provides good bonding with hydroxyl groups in natural fibres, has been used. The results show that there is a potential in using natural fibres for strengthening timber structures.