Have foil faced insulation taked to underside of rafters. Do I need separate VCL?

Folks,

Per thread title, I have tacked sheets of foil faced rigid insulation to the underside of my rafters in the attic (potential future conversion). Given that the sheets are foil faced, do I need to install a separate vapour control layer underneath them (polythene) or is the kingspan sufficient? Thanks in advance, apple1

Er. The silver foil is a function of the manufacturing process and has no bearing on insulation as it will decay pretty quickly.
Vapour control system - not sure what that is.
If your roof is now insulated on the rafters as opposed to the horizontal beams then I would imaging it is not air tight so vapour should not be a problem.

Vapour appears in an airtight insulated space and will drip like a leak. I doubt if you will have this problem. If you have you need to let some air into your attack - counter productive as that might seem.

Hope that helps.