Vermiculite loft insulation

[brickland04]

I have bought an old house and in the loft it has vermiculite insulation. I would like to board it just for storage, etc. and I am wondering what is the best option.
The existing vermiculite is probably only 1" deep and the rafters are 4"x 2"

Should I...
a) remove all vermiculite and replace with rock wool then board it.
b) place rock wool on top of the vermiculite and board it.
c) place kingspan board on top of the vermiculite and board it.
d) any other suggestions?

 

[Deluks]

Leave it in place, lay 100mm rockwool rolls on top and counterbatten, then fix your floor. You'd still have just enough space to fix some 25mm kingspan on top of the rockwool between the battens before boarding.

Do a search on here, (the floors,stairs and lost section) for crossbatten or counterbatten.