Joist centres more than 600mm for 18mm board? Talk to a structural engineer for a more detailed spec.
- Before laying check joists are level and that there's no mortar dropping or debris.
- If the joists are treated with water borne preservative, check they're dry before fixing boards.
- Joist moisture content shouldn't be more than 20% - more can make the timbers distort and boards swell locally.
- Lay boards with long edges across supporting joists in a straight line. Centre short edges supported on joists.
- Support short edges on joists/studs or noggins. Any board overhanging a joist must have a noggin supporting it. All edges of a square edged board must be supported
- Always check your bridging and noggin supports to ensure they comply with safety requirements.
- Panel edges must bear no less than 18mm onto joists.
- All OSB flooring can be nailed or screwed just 8mm from the edges.
- If fixing boards to supports, use a fixing with a minimum length of 50mm or 2.5 times the thickness of the panel, which ever is greater and a diameter of 0.16 times the panel thickness. Fixing should be at 150mm centres around the perimeter and 300mm at intermediate joists.
- Gluing panels to joists increases the structural strength of your build.
- Remember to create enough under floor ventilation.
- Use D4 PVA adhesive for all T&G joints.
- Remember to keep the perimeter expansion gaps and check you've got a snug fit with all your T&G joints.
- Square edged and T&G panels need a 10mm expansion gap, or a total of 2mm per metre of boarding - whichever is bigger - left at perimeters and upstands.
- On square edged panels allow a 3mm expansion gap between boards and edges.
- Tongue and Groove already has an expansion gap included in the T&G joint.
Check your flooring manufacturer's instructions on underlayment. Many are happy to work with OSB as a direct under-surface for parquet flooring, thick wood strip, or carpet that's fitted with underlay. There are some adhesives available for direct fixing to OSB, but always check with the adhesive manufacturer for suitability
For more on the design and use of panels in floor decking, check out section 2.4 of ‘Panel Guide' by Wood Panel Industries Federation (WPIF).