Insulation of an old croft roof

[rocky_robin]

My house is a 19th Century croft, where 2 bedrooms are situated upstairs and within the roof area. This is typical with the crofts.

I've insulated under the floor boards downstairs and in-between the floor levels.

My issue is the draughts and lack of insulation in the roof area of the house.
With the snow we've had over the past few days, I see that the house is loosing heat, but also noticed that draughts are coming in past the tiles and down the inside of the walls (between plasterboard and walls)

Is there any way I can insulate this areas? I've already got insulation above the roof of the bedrooms along the crawlling area at the peak, but this is tiny compared to the surface area of the roof!

I know I can't block off the ventilation around that area, but is there anything I can do, other than moving to a modern house!??

I've got lots of polystyrene available as well as the glass wool stuff.

 

[rocky_robin]

Ok.

I've drawn this up on CAD to give you an illustrated description of what I mean above.

I'd like to insulate the walls in the bedroom, but with the small cavity between the roof wood and the plasterboard, it seems to be difficult to keep the ventilation flow.

 

[rocky_robin]

Anyone willing to give advise?

I've got the insulation in the correct flat roofing spaces, but would this not be similar to a loft conversion? Although, nailing insulation boards onto the tile battons will be impossible, unless the walls came down!