ISO 19821:2017 specifies the procedures to establish a span rating for natural fibre-reinforced plastic composite (NFC) deck boards and deck boards used as stair treads, provided that the stair treads are produced from the same materials and processing techniques as the deck boards. This document covers test methods of performance, acceptance criteria and determination of span rating. It is intended to establish the basis for code recognition of deck boards used in exterior applications where combustible construction is allowed.