Insulating window framing (Passive House style) worth it? – GreenBuildingAdvisor

Building an addition in CZ 6b/7, elevation 6600′, 386 lb/sqf ground snow load.  Average winter temp is 11F (4 months).  11F is not that cold, but the temps regularly drop below 32F throughout the year, including shoulder season, which puts us in CZ 6b/7 (8600 HDD (65F) in warm years, 9200 HDD (65F) in cold years).  So not extreme cold, just lots of regular cold.

We are installing Loewen double-pane casements/awnings/direct sets with i89 (S4) and e180 (S2) coatings.

We are trying to figure out if it makes sense to buck out the windows so that they are flush with the exterior (current thinking), or take a more passive house approach and (a) install the windows mid-wall for better performance and (b) then further insulate the frames.

Our concern is that the energy ROI on the mid-wall install will likely be measured in decades, seeing that the frame represents a small amount of surface area.  But it’s also an area for thermal bridging, and how that will impact comfort when near the windows.  On the other hand, it’s also a higher level of detailing, which can change the risk-reward balance.

Our wall stack, inside to outside:

3/8″ finished decorative interior cedar

5/8″ sheetrock

2×6 framing, R21 blown in insulation

1/2″ OSB shear ply

Grip0Rite ProWrap -SA

1-1/2″ R6 Rockwool Comfortboard

1/2″ roughsawn ply (“batten”)

3/4″ 1×8 red cedar boards (for reverse board and batten)

I’ve seen the thermal maps, and read the Passive House cases, but I’m wondering if anyone here on GBA has done this, and felt it was worth it?

Attached is a sketch of the proposed wall stack with window.