What goes inside a garden room wall?
From outside in: cladding, battens, breather membrane, sheathing, the frame, insulation, vapour layer and lining.
Outside first: the cladding you see, on battens that hold it off the wall so rain behind it can drain and dry. Behind that, a breather membrane that stops water but lets damp vapour out.
Then OSB sheathing to brace the frame, and the timber frame itself with insulation between the studs. On the warm side goes a vapour control layer, then the inside lining.
Skip the insulation and you also skip the vapour layer and lining. That's fine for a summer shed, but it won't be a room you sit in during winter.
Check before you buy or dig
- The vapour layer always goes on the warm, inside face. Put it on the wrong side and the wall can rot from inside.
- Leave a gap at the bottom of the cladding so the air behind it can move.
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See the wall layers for your roomA general answer, not a structural design. Local rules, ground and loads decide the final build.