Insulating a house with wooden cladding and no cavity behind

Our bedroom faces south and the outer skin of the upper storey is made up of dark stained horizontal wooden cladding apparently fixed to the inner block skin by battens, probably no more than 1" thick. There is no vapour barrier we can see and the temperature in the summer is beyond words! The process must be that the dark wood absorbs solar radiation and passes the stored heat to the block material, which then kindly radiates into the bedroom. We are told that to insert a layer of insulating material would require the entire cladding to be removed, insulation material to be placed between battens, a vapour barrier to be fixed over and then the cladding re-applied. I guess the other alternative would be to apply dry lining board with polystyrene layer to the inside walls. Anyone had experience like this? Any suggestions? Any idea how much of a temperature reduction could be achieved by either method?
We are in the south of England and our summers are becoming warmer and longer so this is a problem we need to address.
Thanks
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On 12 Sep 2006 10:53:41 -0700, "peterc"

You could also just add foam-board insulation over the existing cladding, and screw new siding or vinyl through the foam to the wood behind it, but you'd have to re-do the trim around the windows and doors.
THe most you're likely to get out of adding 1" of insulation is around R7 or so. Your existing wall is probably around R3, so the change would reduce your heat-loss/gain through the walls by at best 70%, ignoring air-leaks and windows.
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