Currently decorating our cold attic in a two-story villa from 2005. On the existing (uninsulated) sloped ceiling of tongue and groove panels, we will install an air gap/masonite/240mm insulation/vapor barrier/45mm studs and insulation/gypsum. The gables have wind protection; we insulate these 170mm and install a vapor barrier, 45mm studs and insulation, then gypsum. On the attic floor, we install studs cc30 on top of the floor joists (which are currently filled with 55 cm of loose-fill insulation on top of the vapor barrier in the ceiling of the floor below), lay chipboard and parquet or laminate. We have made an opening and installed stairs up to the attic. So far, no issues.
What I'm wondering is how to connect the vapor barrier at the bottom of the sloped walls and gables to the existing vapor barrier in the floor (i.e., to the plastic in the ceiling of the floor below)?
Do I have to dig down through the loose-fill to the existing vapor barrier in the floor? Or can I extend the vapor barrier from the walls further under the chipboard (or parquet?) and connect it to the downstairs plastic at the stair opening? Or is it sufficient if I extend the vapor barrier at the bottom of the walls a half meter below the new floor and hope that no moisture will find its way out through parquet/chipboard/insulation and further out toward the exterior wall in the attic floor structure?
