Thanks for these thoughts, righto, to be fair to cladco, they spec just 50mm wide, and do not mention depth:
I read a PDF on PlanWell's website (similar company and products) that the horizontal battens/purlins should be at least 50mm square:
I then took that plus pics of people building massive barns and ended up with this concern that I needed 2x4!
This is one of the articles I read about the water build up issue with just horizontal battens on a low pitch roof (ours is 1 in 20), advocating the vertical cross-battens for a drainage channel:
But I am glad to hear your thoughts that counter-battening is not needed. After all people use this metal roof as a single skin, so it cannot be that damp under it. And we keep telling ourselves this is a shed not a house - when learning what to do from internet blogs/videos I do get drawn down the path of full-on house construction but lack the experience to know when that is overkill.
So if I use 2"x1" battens - 50mmx25mm - plus an 11mm OSB roof sheeting then that is 36mm. Cladco's shortest screw is 32mm (and I am assuming that is thread length, not the total length) and that would screw into the OSB but not through
But, without counter-battens, I think there is just enough height to use something like 50mmx38mm then the screw does not go through into the OSB, which seems helpful in case of a slight leak around a fixing head?