I'm in the process of renovating an upstairs room which is built into the eaves of the house (the outer "wall" of the room is lath & plaster directly onto the rafters). The lower part of this wall is boarded to form a cupboard / storage area running the length of the room. One of the jobs is tidying up this cupboard & changing from regular door to sliding doors. As I've got into the job, I've noticed that the area between the outer roof & the plaster in not insulated & trying to figure how to go about insulating it. There seems to be little access from anywhere, so I've been coming to the conclusion that I'll have to strip the plaster, insulate & then re-plaster - does this sound correct? I'm looking at Kingspan K7 type board as the easiest way to do this, but really not sure if I'm on the right lines & am concerned about ventilation / moisture; The house is a 1930/40's two storey, with a slate/felt/boarding double roof, it's got solid concrete soffit's so I'm assuming it's not ventilated. Can I use Kingspan type board here & should there be an air gap between it's top face of the roofing boards? Apologies if any of the terminology is wrong & thanks for any advice.