OSB stands for Oriented Strand Board and is also known as sterling board, it’s a specially engineered wood particle board that’s created by adding adhesives and then compressing layers of wood strands in specific orientations. OSB may have a rough and variegated surface with the individual strips of around 2.5 × 15 cm, lying unevenly across each other and comes in a variety of types and thicknesses.

The product tends to come in four different types, with OSB3 being the preferred choice for fibreglass roofing;

OSB3 has been designed specifically for demanding roofing applications including flat and pitched roofs in both cold and warm configurations along with roof cassettes and dormer windows. The boards are available to purchase in various configurations but we recommend the 18mm 8×2 board with tongue & groove profiled edges.

You don’t have to buy tongue and groove (T&G) but if you can they hold many advantages over the square-edged version that will save you both time and money. The main features of Tongue & Groove boards in GRP roofing are they don’t need any additional fibreglass reinforcement (or bandaging) on the joints and the T&G profile will help prevent the boards from distorting as the system cures.

One side of the OSB3 board has a rough texture (usually on the side with the writing) which, unlike plywood means no surface preparation is required before use, and the board provides the perfect key for the fibreglass materials to bond to.