Ive got a 1902 house in montreal where it gets down to -30C during winter. Usually its about -15C. Its also very humid here. I just bought this place and noticed there is no insulation in the walls which is no surprise. The walls are shiplap cedar. It all looks to be in pretty good shape. The exterior is very old stucco. Might as well be concrete because its so hard. Its never coming off. On top of that is vinyl siding. I wanted to insulate from the outside since the wall cavity is tiny and some places non existant. I was thinking removing the vinyl, then 2inches or maybe more of rock wool then putting up some real cedar siding. I dont think theres an air gap between the wood walls and the stucco siding so that cant be left exposed. I think ill just leave the walls alone from the inside. Anybody know of a problem with this idea?
The only issue I can see is that the rock wool is not sturdy which wouldn't give you anything to anchor your new siding too without building some sort of frame to fasten your siding to.
Now, what we (my parents and I) did on a 1903 farmhouse in Saskatchewan was to use that "rigid insulation" and fastened it to the stucco (concrete if you will). We then covered it vinyl siding, but I don't see any issue with going with cedar siding. This has held up just fine for about 8 years now.