The air moves right up the roof deck and out the ridge vent.
Air seal attic knee wall.
Knee walls may create open useful space from former attics but they are heat loss and homeowner comfort disasters.
In the video it shows batt insulation in the kneewall studs then a piece of polyisocyanurate foam on the attic side of the kneewall.
The conditioned air escapes out the unsealed top of the knee wall where the top plate is attached to the roof rafter.
Install insulation without misalignments compressions gaps or voids in all knee wall cavities.
When possible insulate the slant wall with dense pack cellulose insulate knee walls with dense pack cellulose or fiberglass batts covered with house wrap.
Properly sealing and insulating attic knee walls can significantly reduce air leakage and heat loss between the conditioned space and the unfinished attic.
The insulation in the knee walls of an attic is usually uncovered on the attic side.
Install a continuous air barrier on the exterior side of the attic knee wall framing with a rigid air.
Explanation offered in the video is that.
It is important to choose an air barrier and insulation material that will reduce the air leakage and heat loss as much as possible.
Fiberglass batts work best if they re enclosed and air sealed on all 6 sides.
Seal attic bypasses before insulating.
Adding a rigid foam air barrier to the cold side of the batt is a great way to take care of this issue on a knee wall between finished and unfinished attic space.