In boat building industry, environmental legislations promoting recycling of thermoset composites have been the main driver globally. Recycling of glassreinforced plastics (GRP), which is widely used in the industry, has been very problematic due to its inherent heterogeneous structure. Considering the urgent need of the industry, several investigations have been carried out to find the beneficial uses of GRP recyclate after mechanical recycling which is the most cost-effective technique. In this study that can be considered an effort to find proper way to recycle GRP containing polyester as the matrix, the recyclate of waste GRP boat material was adopted as modifier for bitumen-based roof covering materials. Fine grounded GRP recyclates were added to the hot bitumen mix with the dosages of 1, 3, 5, 10, 20 and 30 % as a part of roof covering material production process. Performances of the modified end product have been tested conventionally. The tests were also repeated for environmentally aged blends that contain 30 % of GRP recyclate. Results indicate that use of GRP recyclate in the modification of bitumen-based materials is an effective way to improve roof covering materials' performance in terms of temperature susceptibility in particular and has the potential to solve the recycling problems of the industry.Keywords Glass-reinforced polyester waste Á Bitumen-based roof covering material Á Boat building Á Aging