Double 2×4 wall detail – concerns over potential for moisture in the wall – GreenBuildingAdvisor

I am located in western New York State (Climate Zone 6).

I am putting an addition onto an existing farmhouse and trying to use a wall section that is simple, easily buildable and breathable. My thought is to stick with more conventional building materials rather than try to use ZIP system or ZIP-R panels.  I am planning to do a lot of the work myself after the framing is completed.

I am proposing vinyl siding, Tyvek Homewrap (taped), 7/16″ OSB sheathing, exterior 2×4 stud wall with R-15 rockwool , interior 2×4 stud wall with R-15 rockwool, and Drywall, painted.  the wall will be basically 8 inches thick and i would like to use a 2×8 for my sill plate and a 2×8 for my top second top plate to unify the two 2×4 walls.

My question is where to put the air barrier/vapor retarder  AND would a smart vapor barrier be advisable.  I would prefer to put it in between the two 2×4 walls because that will be easy to install and will have minimal penetrations in it.  That would allow me to treat the interior 2×4 wall as a service cavity for electrical wiring and boxes.

I think my wall section will be pretty breathable and should dry well, but I am concerned that the vapor retarder will accumulate moisture since I think the temp will be in the range where condensation may occur during the heating season.  I realize my wall sheathing is proposed to be on the outside and i am not proposing to have any continuous insulation, however, I refer to the guidance concerning continuous insulation and determining the approximate location for the dew point.

The Mean temperature for Dec, Jan, and Feb at my location is 25 degrees F.

Is it reasonable to calculate that the middle of the wall should still be above the dew point and therefore moisture is unlikely to accumulate on the vapor retarder?  Am I missing something?

Finally, I realize this is only an addition on an existing house that is probably fairly leaky.  I’m just trying to to the best i can with the addition