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Orientation of plywood on top of joist, does it really matter?
Anonymous user 09/03/2024 - 3.03 PM
I have heard that when putting plywood sheets on top of joists they should be perpendicular to them. Doe it really matter if, let's say, the playwood sheet has a square shape? Or does the plywood sheet for example 2240x1220 has fibres oriented along the longest side (2440) and so they need to be perpendicular to joists to maximise strength? Thank you
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6 Answers
Anonymous user
Ply should always be laid with the grain running across the joists, not along the joist, to maximise the strength. Laying them length ways down a joist will cause them to crack along the grain which could end up in serious injury and or damage. The smaller the gap between joists the stronger the board will be. Minimum depth of ply should be no less than 12mm.
Answered16 July 2019
2
RMB joinery
Rating: 5 out of 5
It is usually correct to lay sheet material across the direction of the joists, this ensures even distribution of loading on joists, however, plywood is cross laminated so each layer is of different direction providing a strong floor covering. Either way the plywood can be layer providing the joists support the underside.
Answered16 July 2019
2
Michael Cattanach Joiner
Rating: 5 out of 5
Plywood sheets should be laid longest side (2440 mm) at 90 degrees to joists , also sheets should be staggered so that end of sheets don't all land on the same joist . This is generally accepted as the strongest way of fitting.
Answered16 July 2019
2
KDF
Rating: 4.6 out of 5
You're correct in that they should all be fitted across joists and not along. Stagger the joints and don't worry about if its square, just make sure ends are supported.
Answered15 July 2019
1
Timothy David Interiors
Rating: 5 out of 5
Seems you have overthinked this. If the sheet is dimensionally mirrored, then no lay it any direction
Answered13 July 2019
0
Mark jones
No reviews yet
You should always cross bond and the distance between timbers will dictate thickness of ply needed
Answered29 January 2021
0