We removed the old thin stuff but if you've got the space I imagine you could keep it. We did a layer between the joists then a layer perpendicular across the tops of them, hence needing to raise the floor level. Important to look at any wires up there and keep them on top of the insulation if you can and if you put a floor over it keep a bit of an air gap
We removed the old thin stuff but if you've got the space I imagine you could keep it. We did a layer between the joists then a layer perpendicular across the tops of them, hence needing to raise the floor level. Important to look at any wires up there and keep them on top of the insulation if you can and if you put a floor over it keep a bit of an air gap