Vapor retarder goes on the warm-in-winter side. Interior in IECC zones 5-8 and Marine 4; omit a Class I retarder in hot-humid 1-3A. Climate-zone table inside.
Prescriptive CI R-values by climate zone for steel-stud, wood-frame, and mass walls, plus the rainscreen wall section that keeps the dew point outboard.
Air barrier stops air leakage, the WRB sheds bulk water, the vapor retarder controls diffusion. The building-science distinction every detailer needs.
The correct window flashing sequence: sill pan first, jambs over the fin, head last under the WRB. Drain to the exterior, shingle-lap, avoid the two cardinal sins.
How to detail parapet coping and counterflashing right: inboard slope, continuous cleats, drip edges, reglet-set counterflashing, base flashing height, thermal joints.
