Timber is one of the oldest building materials and is very attractive because it is a renewable resource, recyclable and relatively inexpensive. However, as the service requirements that are imposed on structural members change, mechanical upgrade or repair becomes of increasing importance. This paper describes an experimental test programme which investigates the use of glass fibre reinforced polymer rods (GFRP) for the retrofit of low-grade glue-laminated timber beams, which were tested in bending initially in the unreinforced state for both stiffness and ultimate moment capacity. The test results demonstrated that by correctly carrying out the retrofitting procedure in timber beams that were severely damaged, mechanical strength and flexural stiffness of the original beams could be regained and in addition significant ductility was introduced.