That does not seem adequate for racking resistance of the frame. It would normally need at least an 11mm board of some sort on the external face.
My concern is that by the time I have added 11mm to the cladding and batten I'm going over 40mm of overhang and it's going to start looking daft.
Surely there is no difference sheathing the inside face as apposed to the external?
Although I have been advised by my builder that it will be fine without.
In all reality I am building a big shed!
Regards
Sam