- Check joists or rafters are level and that there's no mortar dropping and debris
- Check all supporting joists are straight and level
- If your joists or rafters are treated with water borne preservatives, check they are dry
- Lay OSB panels with the long edges at 90Â° to supports and with your short edge joints staggered
- Always check that your short edges are supported on joists or noggins
- For correct fitting panel edges must bear roughly 20mm into joists
- Decking or sarking with OSB? Use a fixing with a minimum length of 50mm or 2.5 times the thickness of the panel, whichever is greater and a diameter of 0.16 times the panel thickness. Fixing should be at 150mm around the perimeter and 300mm at intermediate studs or joists for flat roof decking and maximum of 200mm for sarking
- Your cross joints on the boards must staggered, do this by placing boards in adjacent rows
- OSB boards and can nailed or screwed up to 8mm from the edges
- Doing a flat roof? Sanded OSB gives you the extra adhesion you need.
- If using square edge sheathing boards, leave a 3mm gap between them. Or, if you're abutting any rigid upstand, make it a 10mm gap - this also applies to the perimeter of the room and up stands where T&G are used.
- Working with long roofs? Aim for a possible overall perimeter and abutment expansion gap of 2mm per metre length of roof and a minimum of 10mm.
- Remember that's on top of the 3mm gap each square edge roof sheathing panel needs.
For more on using panels in flat roof decking and sarking, check out sections 2.5 & 2.6 of â€˜Panel Guide' by Wood Panel Industries Federation (WPIF).