Reroofing and need to increase insulation for Building Control.
Easiest way to get near required insulation figures is to add between rafters 75mm solid PIR insulation with 25mm airgap before breathable roof felt and slates at time of re-roofing.
Was considering adding Vapour barrier between ceiling and existing 100mm glassfibre.
Still will not meet 0.16 U value "required" but hope to negotiate with BC on what is practical, economic and feasible in Victorian rood space. What issues are there in mixing warm and cold loft systems ? Any other economic suggestions etc ? Suggestions on how to negotiate with BC !