leave out the fibreglass, keep the pir, the more the better..
I built a summerhouse in lockdown, 3x2 cls with 60mm pir. Inside of that was 18mm ply for stiffness, plasterboard and skim. dpm on floor joists (6x2 @ 400 ctrs, suspended) followed by 25mm pir and 18mm floorboard then vinyl. roof was...