I am patching horizontal lapped cedar siding on a 1950s house in Minnesota with fiberboard sheathing. I think it’s Nu-Wood. There’s no vapor barrier. I will have to put a vapor barrier per code where I patch (thinking roofing paper). Will I need to take off all siding and install a vapor barrier?
To me, moisture barrier goes on the exterior side of exterior walls and vapor barrier goes on the interior side.
We install moisture barriers because we know siding leaks...especially your type of horizontal lapped siding.
If you are patching a hole (or small area) in the siding, there’s no reason to remove all the siding to install a uniform moisture barrier throughout the wall. I’d just make sure the patched area has an adequate moisture barrier and it’s lapped properly onto the existing moisture barrier before installing the new patched-in siding.