I already have some insulation in the loft but it is not very thick, will this have to be removed or can it be topped up?

You can lay SupaSoft on top of existing insulation although the amount of additional insulation will depend on how much existing insulation is in place and what condition it is in. For instance, if the insulation is in very poor condition we would recommend adding 250mm of SupaSoft on top. However if the existing insulation is in very good condition, add sufficient SupaSoft to achieve a total insulation thickness of 270mm. Check under and around existing insulation for any signs of damp or water damage.