I have 4 pieces (about 50 sq ft) of odd shaped polystyrene foam insulation between 3" and 4" thick. it's leftover from installing a flat roof. creative ideas anyone?
I'm a bit confused here Andy. If the flat roof needs replacing, when it is removed what is revealed is going to be exactly what you would see if you removed the ceilings. So why consider removing the ceilings if they are ok? When the flat roof is replaced put the insulation in then. Whilst rockwool would have been the material to use there is now roofing insulation board that is much more efficient, 50mm board gives equivalent insulation of something like 150mm rockwool. If the flatroof isn't fitted with suitable vents to keep it ventilated fit them when the roof is done too. The only reason I can see for replacing the ceiling plasterboard is if it hasn't got a vapor barrier ie foil backed board.
Use it as insulation in the basement. Place it under the floor along your rim joists above the foundation
