Air barrier and moisture control at window head

Make the interfaces between windows, doors and skylights and wall/ceiling assemblies airtight by sealing all junctions between the polyethylene air barrier and the window, door, or skylight frame (Figures 9 and 10). Overhangs and cantilevered floors over unheated spaces or the exterior and ducts, chimney flue and pipe penetrations must also be made airtight.

Figure 9

Figure 10

Source : Canada Mortgage and Housing Corporation (CMHC)