Been researching this project for a few months now but still can’t decide on the best method!

Its a single wooden garage on a concrete floor. 19mm t&g on an 80x50mm frame.

It will be used mostly as a workshop/place to booze and smoke and brewhouse, so I expect some condensation on brewdays.

Ventilation wise there’s a ventilation gap along roofline at gabled ends which I’ll not block up and I will be putting in an extractor for use above my brew kettle. There’s going to be a recycled aluminium double glazed door put in and diy double glazing. The swing open garage doors will hopefully be insulated same way as walls.

The concrete floor is going to be done with a paint on expoxy for ease of cleaning down but still pondering how to insulate walls and roof. Going to be boarding inside with osb but what to put between that and the t&g?

My budget won’t stretch to kingspan and polystyrene is a bit of a fire risk? I’ve been donated some knauf loft roll 150mm thickness but would need to split this to 50mm to fit between frame allowing for t&g, 25mm air gap, breathable membrane, 50mm insulation, vapour barrier then osb.

Just not sure how to proceed. Do I need both breathable membrane and vapour barrier? Would polystyrene be better? Would I need both membranes with polystyrene?

Confused!

Use polystyrene if the fire reaches it after burning the OSB then your garage is f****d anyway.

Have a look for ‘Earthwool’ sold in batts rather than rolls. Nice and dense, fireproof, comes in different thicknesses and depending on the spacing of the battens in your shed comes in widths that will pretty much just press straight in and stay put. Its made from recycled glass bottles, so although a bit scratchy is nowhere near as dusty or irritating to work with as traditional mineral wool.

As a bare bones approach you could just press in the insulation between the battens and staple tyvek over it so it stays put…. and leave it at that. I’d only bother with the OSB if you don’t want to look at they tyvek.