From what I've seen with old country side houses in France just insulating the roof and the windows can already bring very good results (heat lost through walls

From what I've seen with old country side houses in France just insulating the roof and the windows can already bring very good results (heat lost through walls is usually only around 25% of all the losses). A quick and cheap solution for the roof is to lose the attic and blow the isolating material directly on it.