UK Plywood & OSB Grades Reference

OSB/3 is the minimum grade for structural use in humid conditions (which covers most UK construction). OSB/2 is structural but only for dry conditions (Service Class 1). OSB/4 is heavy-duty structural for humid conditions. For floor decking, roof sarking and wall sheathing, OSB/3 (or OSB/4) is the standard choice in the UK. OSB/1 is non-structural and only suitable for packaging or interior linings.

For domestic floor decking at 400 mm joist centres, 18 mm tongue-and-groove OSB/3 or structural plywood is standard. At 600 mm centres, 22 mm is required. For heavy loads or commercial use, 25 mm may be needed. Always check the manufacturer span tables for the specific product and loading conditions.

Hardwood plywood (birch, tropical hardwood) has denser, stronger plies and is used for furniture, joinery and high-quality applications. Softwood plywood (spruce, pine) is lighter and cheaper, used for structural sheathing, shuttering and general construction. Structural softwood plywood must be CE marked and graded for its intended use.

Yes, provided you use the correct grade. Plywood must be rated CE2+ (EN 636-2 or EN 636-3) for exterior humid or exterior conditions. OSB/3 and OSB/4 are suitable for humid conditions but not prolonged direct weather exposure. For fully exposed external use, marine plywood (BS 1088) or treated structural plywood is recommended.