Using 11mm osb instead of 18mm, is this ok?

15 May 2013
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United Kingdom
Im fixing some tapco tiles to a roof that has 11mm osb board then battens on top. The fixing guide says I need 18mm. I have rafters that are 40cms apart beneath the osb sheet. There Is also a plastic sheet (DPM sheet as its only a field shelter) then sarkit on top of the osb board then 32 x 25mm battens. Will the 11mm board suffice?

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Thanks for your reply woody. I was careful to attach the battens through the osb and into the rafters below but it does flex a little when walking on it so I end up doing an impression of a crab doing a poo to try and spread my weight
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Now the majority of the tiles are up the roof it seems to be gaining rigidity. It seems adding the battens made the flex disappear somewhat also. Another hour up there and i'll have the roof complete (4.8m x 2.4m area).
Theres a couple of areas where I hammered a nail through the tile and it hit a nail that was used for fixing the battening. I just removed it patched it up with sealant and gaffa tape then renailed across slightly.

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