I will insulate my old outbuilding which has single brick walls all the way down to the foundation. As it stands now, it's quite damp and porous in the old plaster near the floor. I have poured a new floating slab on polystyrene with a drainage layer underneath. Due to the ceiling height, the floor is only a few centimeters higher than the ground, and I will also drain outside along the walls. On the floor, I plan to lay tiles without any moisture barrier.
The question is, what solution is best to avoid future moisture problems in the walls? Frame onto the brick with steel studs and add insulation, plastic film, drywall?
Is there any advantage to insulating walls with polystyrene instead of fiberglass in this case?