Detailing exterior foam board on brick/framed interface – GreenBuildingAdvisor

Hello all,

I’m about to install new foam board insulation on an addition attached* to a late-1800’s triple wythe brick farmhouse in zone 5A (central PA). I’ve read a ton and am doing my best to make sure I manage and transition my control layers, but was hoping for an expert opinion on transitioning between the addition and brick house.

Exterior is currently stripped down to original lapboard siding (installed direct to studs, no sheathing). My plan was to install 1″ GPS foam board directly over the lapboard, then install Blueskin WP100 self-adhered WRB as my primary air barrier on the outside before reinstalling vinyl siding on top. I’d prefer not to have to install a rain screen to keep total assembly thickness down.

I don’t plan to cover the brick of the original house, and one brick wall is a “party wall” between the addition and main house. There’s a ~1″ gap between the brick and the 4×6 corner of the addition (pole barn / balloon frame construction–see photos).

Would it make sense to overlap my foam board + siding 12″ over the brick to cut down on thermal bridging and simplify air sealing? I’m concerned with the rest of the addition well-insulated (R13+5) that the uninsulated brick (~R4/ft in the corners…near-zero!) would be prone to moisture buildup / condensation. How should I terminate the foam / WRB where it reaches the brick?