Does anybody know whether it is possible to use some rigid insulation like kingspan over the top of joists ( between which is a currently insufficient thickness of rockwool) .
The reason I would do this would be to allow reboarding, as more rockwool would come over the joists and would not allow the boards to be replaced easily for storage space.
Are there any condensation issues- or could these be avoided by leaving a cm or so gap between the solid insulation boards and reboarding again with a little gap at 90 degrees to this??
If this is realistic what thickness of kingspan or the like, needs to go on 7 cms of rockwool to come up to the equivalent of the 270 mm recommended.
Thanks- Jane