OSB3 11mm twisted - usable?

suburban guy

Hi,
Can someone advise me if my recently purchased 11mm OSB sheets are usable? I intend using them as roof sheathing for a garden shed I'm building (or a least trying to build between downpours). The 4 sheets I bought and had delivered are twisted - both ways, not just bowed in one direction. When I called the supplier I was told that 11mm OSB is notorious for this but it'll sort itself out once applied to the roof or weighted down. Is this true and would I be good to go ahead with installation?! For the last few days I had them weighed down flat beneath the 4x2 wall carcassing and they have straightened, a bit. Do you reckon they'd be ok for cutting and installing (the supplier's quite a bit away from me so it's not a simple matter to return them)?
Thanks in advance.

slimjimmc

Haven't had a problem using them on my shed. They were a bit more awkward to line up joints, mark cuts etc but once screwed down to the joists they were fine.

jack of all

To be expected I'd say- I bought 20 sheets of 12mm shuttering grade ply a couple of months ago and nearly every one of them was twisted, probably as much to do with the poor way they were stored at the suppliers yard as much as anything. Once they were fitted in position and adequately screwed they were fine and I had no problems (300mm centres on studs at 24" centres). 3/4" sheets would be a trickier job. I'd say, as it was easy enough to straighten out the 1/"2 sheets as I fitted them- I did use a couple of clamps to keep things in place while I worked on each sheet, with the crowned face of each sheet (convex face) facing the framing.

suburban guy

Thanks a lot for your useful replies, I won't fret as much knowing now it's a common thing for the sheets to be twisted. Using clamps is a good idea. Should the crowns not be facing upwards for whatever's over them to bear down on them a flatten them out (though in my case it'll be box profile metal so not much weight I guess)?

jack of all

[QUOTE=suburban guy;97282481 Should the crowns not be facing upwards for whatever's over them to bear down on them a flatten them out (though in my case it'll be box profile metal so not much weight I guess)?[/QUOTE]

I don't think so- I found it easier to work with the the convex face fixed to the studs, easier to clamp the sheet edges and screw fix than rely on screws to pull a crowned face in (if you know what I mean). Try one sheet and you'll see what I mean!

suburban guy

I'll give that a try, thanks.