Shed insulating

Hello all. I’m building myself a shed from 2x3’s initially with ply outer walls and flat ply roof covered in epdm but at a later date will add some cladding to the outside walls to make it look nice stood off some smaller battens.

We’ve a load of fibreglass insulation left over at work which I’m not only allowed but encouraged to take to get it out the way so thought I may as well stick it in.

Been reading about the membranes and see some people wrap the whole building in it around the batterns before putting the wall and roof panels over the top, but reading on an insulation suppliers blog they say not to do that and to tack the insulation in the gaps between the batterns inside with an air gap between the wall/roof panels to prevent moisture getting trapped. Which has led me into a bit of confusion.

Does it matter which way it’s done? If I’m wrapping obviously I need the membrane in the building stage and needs to go in the initial costing.

The fibreglass won’t be going in yet - touching up the interior will be the final stage so it matters not to me when it’s done just want to do it the right way.

Also, should I be putting any of this stuff anywhere under the floor?

Depends what you mean by membrane? If you use moisture permeable then no moisture can get trapped.

ply is not waterproof so will need protection

Breathable membrane. Pics I see of people using it wrap the whole carcass in it then put their walls straight on to the membrane. But I’ve read there needs to be an air gap between the membrane and wall.

Yes using exterior grade hardwood and will be well sealed with a few coats of preservative.

you have to be really really careful there is a load off cheap chinease ply about with thinner outer layers so comes up sub 12mm[perhaps 11.5mm] and it wont last will delaminate even iff treated it needs to be protected from water ok for damp but not wet