Is acoustic insulation allowed between attic ceiling and VCL under a warm roof?

[BrianWg]

Completing a self build  that has an Attic room under a pitched roof, construction is over rafter VCL+120mm PIR. Site is on a busy main road and have noticed quite a lot of road noise in the room. Can I fit acoustic insulation (e.g. Rockwool) between rafters (i.e. under the VCL) or would this cause a condensation problem?

[Mr Punter]

The VCL would normally be on the warm side of the rafters and insulation.  If the insulation is above the rafters you should be able to fit some rockwool between them without issues.  You could also fit resilient bar before you plasterboard.

[BrianWg]

Many thanks for your comment - am I being paranoid? - The VCL is on the outer side of the rafters under the insulation so it also acts as an airtight layer - logic being that downlighters can be fitted into the plasterboard ceiling without  penetrating the VCL, My fear is that by adding acoustic  insulation on the inside of the  VCL I create a condensation layer  between the acoustic insulation and VCL  - your thoughts?