What’s the insulation you use? Here in New Zealand we use a product called Pink Batts which is a fibreglass product. It’s nasty stuff but even at its most basic it’s got a degree of fire resistance.
There’s a wool version as well but in general, other than a polystyrene based product most insulation in New Zealand has to meet a minimum fire rating.
Plywood walls would have been a great option then you could use the walls to store stuff. That’s what I’ll be doing with my workshop once I redo the aging bracing.
We used blow in for the ceilings, and fiberglass batts for the sides.
I did not want to go with plywood, since it has all that glue in it. May make the workshop smell in the summer.
Fair call. Here in New Zealand we have a non-toxic ply with a natural glue which removes that problem.